A 2-month-old boy is brought to the emergency department by his mother because of an 8-hour history of difficulty feeding and decreased arousability. His mother says that the symptoms began after he rolled over and fell from the bed. His vital signs are within normal limits. Examination shows regions of purple discoloration in the T4–T10 dermatomes bilaterally and tense fontanelles. Fundoscopy shows bilateral optic disc swelling with dot-and-blot hemorrhages extending to the ora serrata. Which of the following is the most likely diagnosis?

A 47-year-old woman is brought to the emergency department because of pain and swelling in her right ankle after falling from a ladder. She recently emigrated from Brazil and is accompanied by her adult daughter, who sometimes interprets for her because the patient has only elementary proficiency in English. The patient’s medical history is unknown. Vital signs are within normal limits. Examination of the right ankle shows swelling, tenderness to palpation, and a restricted range of movement. The patient is not able to bear any weight on the affected leg. Pulses and sensation are intact over the right foot. An x-ray of the ankle shows an unstable fibular fracture at the level of the syndesmosis. The attending physician decides to admit the patient for surgical treatment and wants to discuss the procedure with her. The patient appears anxious and asks many questions regarding the procedure in Portuguese. The physician has basic proficiency in Portuguese after having spent a semester abroad in Portugal. A professional medical interpreter is not available on-site, but a medical student offers to interpret since she was raised bilingually in English and Portuguese. Which of the following is the most appropriate action by the physician to communicate with the patient?

A 68-year-old man comes to the physician for a follow-up examination, accompanied by his daughter. Two years ago, he was diagnosed with localized prostate cancer, for which he underwent radiation therapy. He moved to the area 1 month ago to be closer to his daughter but continues to live independently. He was recently diagnosed with osteoblastic metastases to the spine and is scheduled to initiate therapy next week. In private, the patient’s daughter says that he has been losing weight and wetting the bed, and she tearfully asks the physician if his prostate cancer has returned. She says that her father has not spoken with her about his health recently. The patient has previously expressed to the physician that he does not want his family members to know about his condition because they “would worry too much.” Which of the following initial statements by the physician is most appropriate?

A 4-year-old girl is brought to the emergency department by her mother 30 minutes after reporting intense pain in both hands. The patient has sickle cell anemia and has been to the emergency department 2 times over the past year because of similar symptoms. Her mother gave her acetaminophen, but the pain continued. Physical examination shows swelling and severe tenderness in her fingers and hands. The diagnosis of an acute sickle cell crisis is established and intranasal fentanyl is ordered for pain control. When the physician informs the patient’s mother, she refuses to give consent for the treatment. She says, “My daughter already has this awful illness, she can’t get addicted to opiates too. I’m a social worker and have seen so many people get hooked on morphine and then overdose. Most of the time they got it from their doctor first!” Which of the following is the most appropriate response by the physician?

A graduate student in public health is conducting a study on population health and is comparing different demographic models. He is particularly interested in investigating health care interventions in societies with the demographic distribution shown. Which of the following measures is most likely to ensure a healthy demographic transition in this population?

A 60-year-old man comes to the physician because of a 1-week history of lower back pain. He has had several episodes of painless hematuria over the past 2 months. Physical examination shows localized tenderness over the lumbar spine. A CT scan shows multiple osteolytic lesions in the body of the lumbar vertebrae. Cystoscopy shows a 4-cm mass in the right lateral wall of the bladder. A photomicrograph of a biopsy specimen is shown. Which of the following is the strongest risk factor for this patient’s condition?

An investigator is studying the relationship between suicide and unemployment using data from a national health registry that encompasses 10,000 people who died by suicide, as well as 100,000 matched controls. The investigator finds that unemployment was associated with an increased risk of death by suicide (odds ratio = 3.02; p < 0.001). Among patients with a significant psychiatric history, there was no relationship between suicide and unemployment (p = 0.282). Likewise, no relationship was found between the two variables among patients without a psychiatric history (p = 0.32). These results are best explained by which of the following?

A group of investigators is evaluating the efficacy of intranasal ketamine in decreasing acute suicidality in teenagers admitted to inpatient psychiatric units. They conducted a pilot study in which 15 participants were randomized to receive intranasal ketamine while 15 participants were randomized to receive a placebo. The investigators ultimately found no statistically significant difference in suicidality after 30 days of follow-up with the level of significance fixed at 5%. They suspect inadequate statistical power. Assuming the investigators intend to keep the level of significance at 5%, which of the following changes would be most effective to increase the statistical power?

A rheumatologist is evaluating the long-term risk of venous thromboembolism in patients with newly diagnosed rheumatoid arthritis by comparing two retrospective cohort studies. In study A, the hazard ratio for venous thromboembolism was found to be 1.7 with a 95% confidence interval of 0.89–2.9. Study B identified a hazard ratio for venous thromboembolism of 1.6 with a 95% confidence interval of 1.1–2.5. Which of the following statements about the reported association in these studies is most accurate?

A group of investigators is studying the association between a fire retardant chemical used on furniture and interstitial lung disease. They use hospital records to identify 50 people who have been diagnosed with interstitial lung disease. They also identify a group of 50 people without interstitial lung disease who are matched in age and geographic location to those with the disease. The participants’ exposure to the chemical is assessed by surveys and home visits. Which of the following best describes this study design?

A geriatric investigator is evaluating the consistency of Alzheimer dementia diagnoses based on clinical symptoms. Patients with known chart diagnoses of Alzheimer dementia were evaluated by multiple physicians during a fixed time interval. Each evaluator was blinded to the others’ assessments. The extent to which the diagnosis by one physician was replicated by another clinician examining the same patient is best described by which of the following terms?

A group of investigators who are studying individuals infected with Trypanosoma cruzi is evaluating the ELISA absorbance cutoff value of serum samples for diagnosis of infection. The previous cutoff point is found to be too high, and the researchers decide to lower the threshold by 15%. Which of the following outcomes is most likely to result from this decision?

A group of investigators conducts a prospective cohort study to evaluate the frequency of guideline-discordant prescriptions of oral anticoagulants for patients with atrial fibrillation in patients with public insurance compared to private insurance. A cohort of 135 healthy patients under 60 years of age with new-onset atrial fibrillation with low risk of stroke and no clinical indication for oral anticoagulant prescription were recruited and followed for 4 years. Results at the end of follow-up are shown:

Based on this information, which of the following values correctly denotes the appropriate measure of association between public insurance status and the likelihood of being prescribed an oral anticoagulant?

An otherwise healthy 13-year-old boy is brought to the physician because of asthma attacks that have been increasing in frequency and severity over the past 4 weeks. He was first diagnosed with asthma 6 months ago. Current medications include high-dose inhaled fluticasone and salmeterol daily, with additional albuterol as needed. He has required several courses of oral corticosteroids. A medication is added to his therapy regimen that results in downregulation of the high-affinity IgE receptor (FcεRI) on mast cells and basophils. Which of the following drugs was most likely added to the patient’s medication regimen?

A 54-year-old woman comes to the emergency department because of sharp chest pain and shortness of breath for 1 day. She has been coughing intermittently, which worsens the pain. She has osteoporosis, for which she takes raloxifene. Arterial blood gas analysis on room air shows:

Physical examination is most likely to show which of the following findings?

A 70-year-old man with a history of hypertension and atrial fibrillation comes to the physician for shortness of breath with mild exertion, progressive weakness, and a dry cough that has persisted for 6 months. He has smoked a pack of cigarettes daily for 45 years. His medications include warfarin, enalapril, and amiodarone. His pulse is 85/min and irregularly irregular. Physical examination shows enlarged fingertips and markedly curved nails. A CT scan of the chest shows clustered air spaces and reticular opacities in the basal parts of the lung. Which of the following is the most likely underlying mechanism of this patient’s dyspnea?

A previously healthy 30-year-old woman comes to the physician because of a 3-month history of progressive shortness of breath and nonproductive cough. She has also had constipation and fatigue during the same period. She has not traveled recently or been exposed to any sick contacts. Physical examination shows injected conjunctivae and tender, erythematous nodules on both shins. The lungs are clear to auscultation. An x-ray of the chest is shown. Which of the following additional findings is most likely in this patient?

A 15-year-old boy is brought to the physician because of recurrent respiratory infections that cause him to miss several weeks of school each year. He also has bulky, foul-smelling stools that are difficult to flush. He has a good appetite and eats a variety of foods. His height and weight are below the 10th percentile. Physical examination shows multiple nasal polyps. There is mild wheezing over the lower lung fields. Further evaluation is most likely to show which of the following?

A 62-year-old woman with hypertension and type 2 diabetes mellitus comes to the physician because of increasing shortness of breath and a dry cough over the past 6 months. She has smoked 1 pack of cigarettes daily for the past 40 years. Chest auscultation shows scattered expiratory wheezes in both lung fields. Spirometry shows an FEV1:FVC ratio of 65% and an FEV1 of 70% of predicted. Her diffusing capacity for carbon monoxide (DLCO) is 42% of predicted. Which of the following is the most likely diagnosis?

A 71-year-old man is admitted to the hospital for evaluation of a 2-day history of difficulty breathing. He has had worsening cough and dyspnea for the past month but refused to see a physician. Two days after admission, he develops respiratory insufficiency. Despite appropriate care, he dies a few days later. The gross appearance of the lung at autopsy is shown. The patient’s pulmonary findings are most likely caused by which of the following?

A 23-year-old woman is brought to the emergency department because of a 2-hour history of shortness of breath. She has a history of atopic dermatitis. She does not smoke or use drugs recreationally. Her temperature is 37.1°C (98.8 F) and respirations are 28/min. She appears anxious and is unable to speak in full sentences. X-rays of the chest are shown. Examination of this patient is most likely to show which of the following sets of findings?

A 32-year-old man is brought to the emergency department by ambulance 30 minutes after being found unconscious on the street. On arrival, he is unresponsive to painful stimuli. His respirations are 5/min and shallow. Physical examination shows pinpoint pupils. Which of the following sets of findings would be expected on arterial blood analysis?

An investigator is studying the effects of influenza virus on human lung tissue. Biopsy specimens of lung parenchyma are obtained from patients recovering from influenza pneumonia and healthy control subjects. Compared to the lung tissue from the healthy control subjects, the lung tissue from the affected patients is most likely to show which of the following findings on histopathologic examination?

A 4-month-old male infant is brought to the physician by his father because of swelling of his left hemiscrotum. He has otherwise been healthy and is gaining weight appropriately. Physical examination shows a nontender left scrotal mass that transilluminates. The mass increases in size when the boy cries but is easily reducible. Which of the following is the most likely underlying cause of this patient’s findings?

A 19-year-old woman comes to the physician because of pelvic pain and vaginal discharge that began 2 days ago. She has no history of serious medical illness and takes no medications. Her temperature is 39°C (102.2°F). Pelvic examination shows pain with movement of the cervix and mucopurulent cervical discharge. A Gram stain of the discharge does not show any organisms. A Giemsa stain shows intracytoplasmic inclusions. The patient’s current condition puts her at increased risk for which of the following complications?

A 39-year-old woman, gravida 4, para 4, comes to the physician because of a 5-month history of painful, heavy menses. Menses previously occurred at regular 28-day intervals and lasted 3 days with normal flow. They now last 7–8 days and the flow is heavy with the passage of clots. Pelvic examination shows a tender, uniformly enlarged, flaccid uterus consistent in size with an 8-week gestation. A urine pregnancy test is negative. Which of the following is the most likely cause of this patient’s findings?

A 17-year-old girl is brought to the physician by her mother because she has not had her menstrual period yet. At birth, she had ambiguous genitalia. The mother reports that during the pregnancy she had noticed abnormal hair growth on her chin. A year ago, the girl broke her distal radius after a minor trauma. She is at the 95th percentile for height and 50th percentile for weight. Physical examination shows nodulocystic acne on the face, chest, and upper back. Breast development is at Tanner stage I. Pelvic examination reveals normal pubic hair with clitoromegaly. A pelvic ultrasound shows ovaries with multiple cysts and a normal uterus. Which of the following is the most likely diagnosis?

An otherwise healthy 8-year-old girl is brought to the physician by her parents because of concern for growth retardation. Although she has always been short for her age, her classmates have begun teasing her for her height. She is at the 5th percentile for height and 25th percentile for weight. Physical examination shows a low-set posterior hairline, increased skin folds along the side of the neck, and a high-arched palate. The nipples are widely spaced and the fourth metacarpal bones are shortened bilaterally. This patient is at increased risk of developing which of the following complications?

A 47-year-old woman comes to the physician because of fatigue, difficulty falling asleep, and night sweats for the past 6 months. Over the past year, her menstrual cycle has become irregular and her last menstrual period was 2 months ago. She quit smoking 2 years ago. Pelvic exam shows vulvovaginal atrophy. A pregnancy test is negative. Which of the following changes is most likely to occur in this patient’s condition?

A 28-year-old woman comes to the physician because she has not had a menstrual period for 3 months. Menarche occurred at the age of 12 years and menses occurred at regular 30-day intervals until they became irregular 1 year ago. She is 160 cm (5 ft 3 in) tall and weighs 85 kg (187 lb); BMI is 33 kg/m2. Physical examination shows nodules and pustules along the jaw line and dark hair growth around the umbilicus. Pelvic examination shows a normal-sized, retroverted uterus. A urine pregnancy test is negative. Without treatment, this patient is at greatest risk for which of the following?

A 2-year-old girl is brought to the physician for a well-child examination. She can run but is unable to walk up and down the stairs. She scribbles and feeds herself with a spoon but she is unable to dress herself. She knows 6 words but is unable to combine different words. She displays selfish behavior when interacting with other children. Which of the following is the most appropriate assessment of her development?

An otherwise healthy 1-month-old girl is brought to the physician because of a 1-day history of multiple episodes of bilious vomiting. She is diagnosed with intestinal malrotation and volvulus and undergoes emergency laparotomy. During surgery, a 3 x 3 cm cystic mass is excised from behind the umbilicus. Microscopic examination of the mass shows mature nonciliated columnar epithelium with some goblet cells lining the inner cyst wall. Dilation of which of the following structures is the most likely cause of this patient’s mass?

A 3-day-old female newborn delivered vaginally at 36 weeks to a 27-year-old woman has generalized convulsions lasting 3 minutes. Prior to the event, she was lethargic and had difficulty feeding. The infant has two healthy older siblings and the mother’s immunizations are up-to-date. The infant appears icteric. The infant’s weight and length are at the 5th percentile, and her head circumference is at the 99th percentile for gestational age. There are several purpura of the skin. Ocular examination shows posterior uveitis. Cranial ultrasonography shows ventricular dilatation, as well as hyperechoic foci within the cortex, basal ganglia, and periventricular region. Which of the following congenital infections is the most likely diagnosis?

A 32-year-old woman comes to the physician because of fatigue, breast tenderness, increased urinary frequency, and intermittent nausea for 2 weeks. Her last menstrual period was 7 weeks ago. She has a history of a seizure disorder treated with carbamazepine. Physical examination shows no abnormalities. A urine pregnancy test is positive. The child is at greatest risk of developing which of the following complications?

A 75-year-old man comes to the emergency department because of right knee pain and general malaise for the past 8 hours. He does not remember any trauma to the right knee. He has an 8-year history of osteoporosis. Three years ago, he was diagnosed with primary hypertension and started on a diuretic. On physical examination, the skin above his right knee is erythematous and tender to palpation. Laboratory studies show mild leukocytosis. Arthrocentesis is performed. Analysis of the synovial fluid under polarized light microscopy shows negatively birefringent needle-shaped crystals. The patient’s diuretic most likely acts on which of the following parts of the nephron?

A 72-year-old multiparous woman comes to the physician for the evaluation of episodes of involuntary urine leakage for the past 6 months. She loses small amounts of urine without warning after laughing or sneezing. She is retired and lives at an assisted-living facility. She has insulin-dependent diabetes mellitus type 2. Her mother received a ventriculoperitoneal shunt around her age. She walks without any problems. Sensation to pinprick and light touch is normal. Which of the following is the primary underlying etiology for this patient’s urinary incontinence?

A 25-year-old woman comes to the physician because of a 2-day history of a burning sensation when urinating and increased urinary frequency. She is concerned about having contracted a sexually transmitted disease. Physical examination shows suprapubic tenderness. Urinalysis shows a negative nitrite test and positive leukocyte esterases. Urine culture grows organisms that show resistance to novobiocin on susceptibility testing. Which of the following is the most likely causal organism of this patient’s symptoms?

A 32-year-old woman comes to the physician because of a 1-week history of left flank pain and dysuria. She has had 2 episodes of urinary tract infection over the past 2 years. Her temperature is 37°C (98.6°F) and pulse is 82/min. An ultrasound of the kidneys shows left-sided hydronephrosis and echogenic foci with acoustic shadowing. A photomicrograph of the urine is shown. The crystals observed are most likely composed of which of the following?

A 62-year-old man comes to the physician because of fatigue and decreased urine output for 2 weeks. He has not been to the physician for many years and takes no medications. Serum studies show a urea nitrogen concentration of 42 mg/dL and a creatinine concentration of 2.3 mg/dL. Urinalysis shows heavy proteinuria. A photomicrograph of a section of a kidney biopsy specimen is shown. Which of the following is the most likely underlying cause of this patient’s symptoms?

A 13-year-old boy is brought to the physician because of swelling around his eyes for the past 2 days. His mother also notes that his urine became gradually darker during this time. Three weeks ago, he was treated for bacterial tonsillitis. His temperature is 37.6°C (99.7°F), pulse is 79/min, and blood pressure is 158/87 mm Hg. Examination shows periorbital swelling. Laboratory studies show:

An investigator is developing a drug for muscle spasms. The drug inactivates muscular contraction by blocking the site where calcium ions bind to the myocyte actin filament. Which of the following is the most likely site of action of this drug?

A 71-year-old hospitalized man develops abnormal laboratory studies 4 days after starting treatment for exacerbation of congestive heart failure. He also has a history of osteoarthritis and benign prostatic hyperplasia. He recently completed a course of amikacin for bacterial prostatitis. Before hospitalization, his medications included simvastatin and ibuprofen. Blood pressure is 111/76 mm Hg. Serum studies show a creatinine of 2.3 mg/dL (previously normal) and a BUN of 48 mg/dL. Urinalysis shows a urine osmolality of 600 mOsm/kg and urine sodium of 10 mEq/L. Which of the following is the most likely explanation for this patient’s renal insufficiency?

A 32-year-old woman with type 1 diabetes mellitus is brought to the emergency department by her husband because of a 2-day history of profound fatigue and generalized weakness. One week ago, she increased her basal insulin dose because of inadequate control of her glucose concentrations. Neurologic examination shows hyporeflexia. An ECG shows T-wave flattening and diffuse ST-segment depression. Which of the following changes are most likely to occur in this patient’s kidneys?

A 21-year-old man is brought to the emergency department by the police because of altered mental status. The police found him covering his ears and shouting near a highway rest area. Upon questioning, he was unable to look directly at the police and answer coherently. On the way to the hospital, he reported feeling nauseous and vomited twice. His temperature is 38.2°C (100.8°F), pulse is 100/min, respirations are 28/min, and blood pressure is 110/77 mm Hg. He is admitted to the hospital for evaluation. Three hours after admission, he has a tonic-clonic seizure. Laboratory studies show:

Arterial blood gas analysis on room air shows:

Which of the following is the most likely explanation of the patient’s laboratory findings?

An 84-year-old man is brought to the physician by the staff of a group home where he resides because of worsening confusion and decreased urinary output. His nurse reports that the patient has not been drinking much for the last 3 days. Examination shows a decreased skin turgor and dry oral mucosa. His pulse is 105/min and blood pressure is 100/65 mm Hg. His serum creatinine is 3.1 mg/dL and a urea nitrogen is 42 mg/dL. Urine studies show multiple brownish granular casts. Which of the following processes is most likely involved in the pathogenesis of this patient’s condition?

A 34-year-old woman is brought to the emergency department by her roommate because of a 2-hour history of increased thirst and erratic behavior. The roommate says that the patient returned home from a party and began to touch pillows and blankets in the apartment and profess her intensely positive feelings and affection for the world. The roommate also reports that the patient often uses recreational drugs at parties. On arrival, the patient is diaphoretic and oriented only to person. Her temperature is 39°C (102.2°F), pulse is 114/min, and blood pressure is 156/102 mm Hg. Neurologic examination shows tremulousness and bilateral pupillary dilation. Serum studies show a sodium concentration of 130 mEq/L. This patient is most likely intoxicated with which of the following substances?

Two days after undergoing uncomplicated total knee replacement, a 55-year-old man develops increasing anxiety, agitation, hand tremor, and nausea. He told the nurse he saw a bear in his room. His pain has been controlled with intravenous morphine. He has a history of advanced liver disease. He drinks 7 cans of beer daily. He is diaphoretic. His temperature is 37.6°C (99.7°F), pulse is 118/min, respirations are 18/min, and blood pressure is 146/92 mm Hg. Administration of which of the following drugs is the most appropriate next step in treatment?

A 29-year-old man comes to the physician for worsening restlessness over the past several days. Three weeks ago, he was started on trifluoperazine for the treatment of schizophrenia. He reports that, since then, he has often felt compelled to pace around his house and is unable to sit or stand still. He is switched to an alternative antipsychotic medication. Four weeks later, the patient reports improvement of his symptoms but says that he has developed increased drowsiness, blurred vision, and dry mouth. The patient was most likely switched to which of the following drugs?

A 28-year-old man is brought to the physician by his wife because she is worried about his unusual behavior. Two weeks ago, he was promoted and is now convinced that he will soon take over the firm. He has been working overtime at the office and spends most of his nights at parties. Whenever he comes home, he asks his wife to have sex with him and rarely sleeps more than 3 hours. He has a history of a similar episode and several periods of depression over the past 2 years. He currently takes no medications. He appears impatient, repeatedly jumps up from his seat, and says, “I have more important things to do.” There is no evidence of suicidal ideation. Urine toxicology screening is negative. Long-term treatment with lithium is started. Which of the following parameters should be regularly assessed in this patient while he is undergoing treatment?

A 27-year-old man with seizure disorder is brought to the emergency department by his girlfriend after falling while climbing a building. The girlfriend reports that he was started on a new medication for treatment of depressed mood, low energy, and difficulty sleeping 2 weeks ago by his physician. She says that he has had unstable emotions for several months. Over the past 3 days, he has not slept and has spent all his time “training to climb Everest.” He has never climbed before this period. He also spent all of his savings buying mountain climbing gear. Physical examination shows ecchymoses over his right upper extremity, pressured speech, and easy distractibility. He is alert but not oriented to place. Which of the following drugs is the most likely cause of this patient’s current behavior?

A 16-year-old girl is brought to the physician for a physical examination prior to participating in sports. She has no history of serious illness. She is on the school’s cheerleading team and is preparing for an upcoming competition. Menarche was at 13 years of age, and her last menstrual period was 4 months ago. She is 167 cm (5 ft 6 in) tall and weighs 45 kg (99 lb); BMI is 16.1 kg/m2. Examination shows pale skin with thin, soft body hair. The patient is at greatest risk for which of the following complications?

A 24-year-old man comes to the physician with a wound on his forearm. He says that he injured himself by absentmindedly walking into a glass door. He has had 5 jobs in the past 8 months. He quit each job after 3–4 weeks because he found the work beneath him. He was imprisoned 6 years ago for credit card fraud. He was released from prison on parole a year ago. He was expelled from school at the age of 13 years for stealing school property and threatening to assault a teacher. He has fathered 6 children with 4 women. He says that he does not pay child support because he needs the money for his own personal expenses. Examination of the forearm shows a 6 cm long, 0.5 cm deep wound with neat edges on the dorsal surface of the left forearm. There are bruises on the left shoulder, back, and the proximal phalanges of the right hand. On mental status examination, the patient is alert and calm. His mood is described as cheerful. His thought process, thought content, and speech are normal. Which of the following is the most likely diagnosis?

A 34-year-old man comes to the physician with a 2-month history of difficulty concentrating at work. He is worried he may lose his job due to poor performance. He feels constantly tired but attributes his fatigue to waking up early most mornings and being unable to fall back asleep. His wife has noticed that he has been speaking more slowly than usual and his appetite has decreased. He used to enjoy dance classes with her but has not been as interested in this recently. He is a veteran who returned from a deployment to Afghanistan 2 years ago. Which of the following is the most likely diagnosis?

A 26-year-old man is brought to the emergency department by his wife because of unusual and agitated behavior for the last 6 weeks. He is convinced that the National Security Agency is spying on him and controlling his mind. He lost his job because he stopped going to work 4 weeks ago. Since then, he has been working on an invention that he says will block people from being able to control his mind. His wife reports that he has stopped all social contact. Physical and neurologic examinations show no abnormalities. On mental status examination, he is confused and suspicious with marked psychomotor agitation. His speech is disorganized, and his affect is labile. Which of the following is the most likely diagnosis?

A 21-year-old woman is brought to the emergency room 1 hour after she ingested 12 pills of acetaminophen. She had a fight with her boyfriend immediately prior to the ingestion, during which she threatened to kill herself if he broke up with her. She has been hospitalized 4 times for overdoses in the past 3 years following breakups with her partners. On the way to the hospital, she screamed and then assaulted the paramedic who attempted to take her temperature. Physical examination shows multiple rows of well-healed scars bilaterally on the wrists. This patient is most likely to display which of the following defense mechanisms?

A 46-year-old man comes to the physician for a follow-up evaluation one week after being discharged from the hospital for acute pancreatitis and alcohol withdrawal. He drinks 8 to 10 beers daily. When the physician asks him about his alcohol use, the patient says, “This is the second time in a year that I have experienced such severe belly pain because of my pancreas. I realize that it really could be happening because of the amount of alcohol I am drinking. However, I don’t think I have the willpower to cut down.” This patient is most likely in which of the following stages of behavioral change?

A 52-year-old man is brought to the emergency department 30 minutes after his farmhand found him on the ground sweating profusely. On arrival, he is lethargic and unable to provide any history. His temperature is 37.5°C (99.5°F), pulse is 42/min, and blood pressure is 95/60 mm Hg. Physical examination shows diaphoresis and excessive salivation. The pupils are constricted. There is scattered expiratory wheezing throughout both lung fields. His clothes are soaked with vomit, urine, and feces. A drug with which of the following mechanisms of action is most appropriate for this patient?

A 21-year-old woman is brought to the emergency department following a motor vehicle collision. She has significant pain and weakness in her right arm and hand. Physical examination shows multiple ecchymoses and tenderness in the right upper extremity. She is able to make a fist, but there is marked decrease in grip strength. An x-ray of the right upper extremity shows a midshaft humerus fracture. Which of the following structures is most likely injured?

A 44-year-old man is brought to the physician by his father. Over the past year, the patient has become progressively forgetful and withdrawn. He frequently has trouble remembering names of acquaintances, and has been requiring increasing amounts of assistance with getting dressed, cooking, and personal hygiene. He was diagnosed with a genetic disorder during infancy. Physical examination shows prominent epicanthal folds, low-set small ears, and a protruding tongue. Mental examination shows significant deficits in short- and long-term memory. This patient’s cognitive symptoms are most likely the result of which of the following neuropathologic changes?

A 27-year-old man comes to the emergency department for progressive weakness and numbness in his legs for 5 days. Symptoms originally started with tingling in both feet and have progressed to involve the knees and hips; he is currently unable to walk without assistance. Two weeks ago, the patient had diarrhea that subsided without antibiotics. Neurologic examination shows weakness, decreased sensation, and absent patellar reflexes in both lower extremities. Lumbar puncture shows elevated CSF protein and no white blood cells. Which of the following structures is most likely affected in this patient?

A 5-year-old boy who recently emigrated from Nigeria is brought to the emergency department because of a 2-day history of lower leg weakness, swallowing difficulty, and drooling of saliva. He has not yet received any childhood vaccinations. Two days after admission, the patient develops shortness of breath. Pulse oximetry shows an oxygen saturation of 64%. Despite resuscitative efforts, the patient dies of respiratory failure. At autopsy, examination of the spinal cord shows destruction of the anterior horn cells. Neurological examination of this patient would have most likely shown which of the following findings?

A 23-year-old man comes to the physician because of severe daytime sleepiness and random episodes of falling asleep during the day for short periods of time. When he wakes up from these episodes, he feels refreshed. He sleeps 6–7 hours at night. He reports that sometimes he is unable to move for a few minutes when he first wakes up in the morning. Last week, he suddenly “lost control” of his legs and neck for about 30 seconds after his classmate had told him a joke. An analysis of this patient’s cerebral spinal fluid is most likely to show which of the following findings?

A previously healthy 50-year-old woman is brought to the emergency department 30 minutes after she was observed having a seizure. On arrival, she is conscious and reports that she feels drowsy. An MRI of the brain shows a 4-cm, round, sharply demarcated mass. She undergoes resection of the mass. A photomicrograph of a section of the resected specimen is shown. This patient’s mass is most likely derived from which of the following?

One hour after undergoing a surgical repair of a thoracic aortic aneurysm, a 70-year-old man experiences severe pain at the thoracolumbar junction and weakness and numbness in both legs. He appears pale and anxious. His temperature is 36.0°C (96.8°F), pulse is 95/min, respirations are 20/min, and blood pressure is 95/65 mm Hg. Physical examination shows decreased sensation to pain and temperature below the level of the umbilicus. Muscle strength is 1/5 in the lower extremities. Proprioception and vibration sense are normal in both lower extremities. Sensation and motor function in the upper extremities, chest, and back are intact. Which of the following is the most likely diagnosis?

A 20-year-old man comes to the physician because of worsening gait unsteadiness and bilateral hearing loss for 1 month. He has had intermittent tingling sensations on both cheeks over this time period. He has no history of serious medical illness and takes no medications. Audiometry shows bilateral sensorineural hearing loss. Genetic evaluation shows a mutation of a tumor suppressor gene on chromosome 22 that encodes merlin. This patient is at increased risk for which of the following conditions?

A 30-year-old woman comes to the physician because of numbness, fatigue, and blurry vision for 1 week. The symptoms are worse after a hot shower or bath. She had an episode of right arm weakness 2 years ago that resolved without intervention. She recently returned from a hiking trip in upstate New York. Her temperature is 37.8°C (100°F) and blood pressure is 100/66 mm Hg. Physical examination shows decreased sensation to light touch in the left hand, right thigh, and right flank. Strength is normal. There is left-sided photophobia and pupillary constriction in the left eye is decreased compared to the right eye. Which of the following best describes the pathogenesis of the disease process in this patient?

A 78-year-old left-handed woman with hypertension and hyperlipidemia is brought to the emergency room because of sudden-onset right leg weakness and urinary incontinence. Neurologic examination shows decreased sensation over the right thigh. Muscle strength is 2/5 in the right lower extremity and 4/5 in the right upper extremity. Strength and sensation in the face are normal but she has difficulty initiating sentences and she is unable to write her name. The most likely cause of this patient’s condition is an occlusion of which of the following vessels?

A 68-year-old man is brought to the emergency department because of a severe headache, nausea, and vomiting for 30 minutes. Forty-five minutes ago, he fell and struck his head, resulting in loss of consciousness for 1 minute. After regaining consciousness, he felt well for 15 minutes before the headache began. On arrival, the patient becomes rigid and his eyes deviate to the right; he is incontinent of urine. Intravenous lorazepam is administered and the rigidity resolves. Which of the following is the most likely cause of the patient’s condition?

A 39-year-old man is brought to the physician by his wife because of personality changes over the past year. He has become increasingly irritable, loud, aggressive, and impulsive. His wife also reports jerky movements of his limbs and trunk for the past few months. His father had dementia in his mid-40s, but the details of his condition are unclear. The patient appears restless. Examination shows irregular movements of the extremities and twitching of the face and tongue. Mental status examination shows impaired memory. This patient’s condition is most likely associated with which of the following changes on MRI?

A 52-year-old man with a history of gastric cancer that was treated with subtotal gastrectomy dies in a motor vehicle collision. At autopsy, examination of the spinal cord shows unilateral atrophy of the neurons in the area indicated by the arrow. Neurological examination of the patient when he was still alive would most likely have shown which of the following findings?

A 55-year-old woman comes to the physician because of a 5-month history of weakness of the left side of her face, loss of taste, as well as dryness and redness of her left eye. She has no history of serious illness and takes no medications. Physical examination shows an inability to puff the left cheek and close her left eye. An MRI of the brain shows a contrast-enhancing mass in the posterior fossa. The patient’s symptoms are most likely caused by compression of which of the following structures?

A 56-year-old man comes to the physician because of worsening double vision and drooping of the right eyelid for 2 days. He has also had frequent headaches over the past month. Physical examination shows right eye deviation laterally and inferiorly at rest. The right pupil is dilated and does not react to light or with accommodation. The patient’s diplopia improves slightly on looking to the right. Which of the following is the most likely cause of this patient’s findings?

A 60-year-old man comes to the physician because his wife has noticed that his left eye looks smaller than his right. He has had worsening left shoulder and arm pain for 3 months. He has smoked two packs of cigarettes daily for 35 years. Examination shows left-sided ptosis. The pupils are unequal but reactive to light; when measured in dim light, the left pupil is 3 mm and the right pupil is 5 mm. Which of the following is the most likely cause of this patient’s ophthalmologic symptoms?

A 78-year-old man comes to the emergency department because of sudden-onset loss of vision. He has hypertension and type 2 diabetes mellitus. Current medications include hydrochlorothiazide, atenolol, metformin, and glipizide. Ophthalmologic examination shows a visual field defect in the bilateral right upper quadrants. A lesion in which of the following labeled sites in the schematic overview of the visual pathway is most likely?

A 53-year-old man comes to the physician for a follow-up examination after an open fracture of the right tibia. Three months ago, he went on an expedition to Egypt, where he fell down while running away from a snake. He was treated with open reduction and internal fixation. He reports that, since his fall, his leather hat no longer fits. He has also had progressive hearing loss over the past year. He works as a professor of archeology. He takes ibuprofen for bone pain. Physical examination shows bowing of the right leg. Which of the following changes in bone architecture is the most likely underlying cause of this patient’s symptoms?

A 56-year-old woman comes to the physician because of a 3-month history of progressive weakness. She has no history of serious illness and takes no medications. Her vital signs are within normal limits. Physical examination shows a violaceous rash over her eyelids. A photograph of her hands is shown. Muscle strength is 4/5 at the shoulders and hips but normal elsewhere. This patient is at greatest risk for which of the following conditions?

A 23-year-old man comes to the physician for frequent and painful urination. He has also had progressive painful swelling of his right knee over the past week. He is sexually active with two female partners and uses condoms inconsistently. His mother has an autoimmune disease that involves a malar rash. Examination shows conjunctivitis bilaterally. The right knee is warm, erythematous, and tender to touch; range of motion is limited. Laboratory studies show an erythrocyte sedimentation rate of 62 mm/h. Urinalysis shows WBCs. Further evaluation of this patient is most likely to reveal which of the following?

A 42-year-old woman comes to the physician because of a 10-month history of joint pain and stiffness in her wrists and fingers. The symptoms are worse in the morning and improve with activity. Physical examination shows swelling and warmth over the MCP and wrist joints in both hands. An x-ray of the hands is shown. Synovial biopsy from an affected joint would most likely show which of the following?

A 51-year-old woman comes to the physician because of a 1-year history of occasional discoloration and tingling in her fingers. She has no history of major medical illness and takes no medications. Examination of the hands and fingers shows thickened, waxy skin and several firm white nodules on the fingertips. Further evaluation of this patient is most likely to show which of the following findings?

A 32-year-old woman comes to the physician because of a 4-day history of low-grade fever, joint pain, and muscle aches. The day before the onset of her symptoms, she was severely sunburned on her face and arms during a hike with friends. She also reports being unusually fatigued over the past 3 months. Her only medication is a combined oral contraceptive pill. Her temperature is 37.9°C (100.2°F). Examination shows bilateral swelling and tenderness of the wrists and metacarpophalangeal joints. There are multiple nontender superficial ulcers on the oral mucosa. The detection of antibodies directed against which of the following is most specific for this patient’s condition?

A 32-year-old woman comes to the emergency department because of a 3-hour history of severe nausea, vomiting, tremor, and anxiety. She recently started a new medication but does not remember its name. She has a history of major depressive disorder treated with fluoxetine. Her temperature is 38.9°C (102.1°F), pulse is 132/min, respirations are 22/min, and blood pressure is 152/94 mm Hg. She is confused. Physical examination shows diaphoresis and an ataxic gait. Patellar reflexes are 4+ bilaterally. Which of the following medications is the most likely cause of this patient’s presentation?

A 36-year-old woman comes to the physician because of blurred vision and difficulty keeping her eyes open. She also has occasional difficulty chewing, especially when eating meat or other foods that require prolonged chewing. The symptoms are worse at the end of the day. Physical examination shows bilateral drooping of the eyelids, which becomes more pronounced when she is asked to look upwards for 30 seconds. Which of the following is the most likely cause of this patient’s symptoms?

A 55-year-old man is brought to the emergency room because of fever and increasing confusion for the past 2 days. He has paranoid schizophrenia treated with chlorpromazine. He appears diaphoretic. His temperature is 40°C (104°F), pulse is 115/min, respirations are 31/min, and blood pressure is 158/105 mm Hg. Neurologic examination shows psychomotor agitation and incoherent speech. There is generalized muscle rigidity. His deep tendon reflexes are decreased bilaterally. Serum laboratory analysis shows a leukocyte count of 11,300/mm3 and serum creatine kinase concentration of 945 U/L. The most appropriate drug for this patient acts by inhibiting which of the following?

A 67-year-old man comes to the physician because of a lesion on his nose. The lesion appeared 1 year ago and has slowly increased in size since then. There is no associated pain or pruritus. He is otherwise healthy and has played golf every other day since his retirement. He says that he used to use tanning beds regularly in the past because he “liked the tanned look.” A photograph of the lesion is shown. Which of the following is the most likely diagnosis?

A 54-year-old woman comes to the physician because of painful blisters under the arms that appeared 3 days ago. She has also had a 2-month history of intermittent, painful lesions in the mouth. Examination of the mouth shows several erosions on the buccal mucosa and lips. Examination of the trunk shows multiple flaccid blisters with a diameter of approximately 2 cm in both armpits. Skin biopsy specimens obtained from the area around the lesions show detachment of keratinocytes within the stratum spinosum. This patient’s condition is most likely caused by autoantibodies directed against components of which of the following cell junctions?

A 17-year-old boy comes to the physician because of a nonpruritic rash on his chest for 1 week. He returned from a trip to Puerto Rico 10 days ago. He started using a new laundry detergent after returning. He has type 1 diabetes mellitus controlled with insulin. His mother has Hashimoto thyroiditis, and his sister has severe facial acne. Examination of the skin shows multiple, nontender, round, hypopigmented macules on the chest and trunk. There is fine scaling when the lesions are scraped with a spatula. Which of the following is the most likely underlying mechanism of this patient’s symptoms?

A previously healthy 5-year-old boy is brought to the physician because of increasing weakness and a retroauricular rash that started 2 days ago. The rash spread rapidly and involves the trunk and extremities. Last week, he had a mild sore throat, pink eyes, and a headache. His family recently immigrated from Ethiopia. His immunization status is unknown. The patient appears severely ill. His temperature is 38.5°C (101.3°F). Examination shows tender postauricular and suboccipital lymphadenopathy. There is a nonconfluent, maculopapular rash over the torso and extremities. Infection with which of the following is the most likely cause of this patient’s symptoms?

A 2850-g (6-lb 5-oz) newborn is delivered at term to a 19-year-old primigravid woman via normal spontaneous vaginal delivery. The mother has had no prenatal care. Examination of the newborn in the delivery room shows a small, retracted jaw and hypoplasia of the zygomatic arch. This patient’s condition is most likely caused by abnormal development of the structure that also gives rise to which of the following?

A 39-year-old man comes to the physician because of a 4-month history of yellow discoloration of the skin. He reports a loss of appetite. He lives with his wife and three children in a rural town where he has been working as a safety inspector at the local nuclear power plant for the past 20 years. He is not physically active and his diet consists mostly of donuts and highly caloric processed food. He does not smoke but drinks 5 cans of beer daily. He is 182 cm (6 ft) tall and weighs 101 kg (222 lb); BMI is 30 kg/m2. His vital signs are within normal limits. Physical examination shows jaundice of the skin and scleral icterus. There is a palpable, round, nontender mass below the right costal margin. Scratch marks are seen on the extremities. Which of the following is the most likely cause of this patient’s symptoms?

A 42-year-old woman comes to the emergency department because of a 2-day history of right upper abdominal pain and nausea. She is 163 cm (5 ft 4 in) tall and weighs 91 kg (200 lb); her BMI is 34 kg/m2. Her temperature is 38.5°C (101.3°F). Physical examination shows a distended abdomen and right upper quadrant tenderness with normal bowel sounds. Laboratory studies show:

A 51-year-old man comes to the physician for follow-up evaluation. Nine months ago, he was diagnosed with acute viral hepatitis B infection. Physical examination shows no abnormalities. Serum studies show increased hepatic transaminase activity and a hepatitis B viral DNA load of 4286 IU/mL. Which of the following sets of findings is most likely in this patient?

A 65-year-old man comes to the physician because of progressive abdominal distension and swelling of his legs for 4 months. He has a history of ulcerative colitis. Physical examination shows jaundice. Abdominal examination shows shifting dullness and dilated veins in the periumbilical region. This patient’s abdominal findings are most likely caused by increased blood flow in which of the following vessels?

A 21-year-old man comes to the physician because of a 6-month history of severe abdominal pain, bloating, and episodic diarrhea. He has also had a 5-kg (11-lb) weight loss during this time. Physical examination shows a mildly distended abdomen, hyperactive bowel sounds, and diffuse abdominal tenderness. A biopsy specimen of the colonic mucosa shows scattered areas of inflammation with fibrosis and noncaseating granulomas. Which of the following is most likely involved in the pathogenesis of this patient’s condition?

Two days after delivery, a 3470-g (7-lb 10-oz) newborn has an episode of bilious vomiting. He has not yet passed meconium. He was born at term to a 26-year-old woman; pregnancy and delivery were uncomplicated. His vital signs are within normal limits. Examination shows a distended abdomen. There is tympany to percussion. Digital rectal examination shows elevated sphincter tone; when the finger is removed, there is an explosive release of stool and air. An x-ray of the abdomen shows a massively dilated colon proximal to a narrowed segment of colon. Which of the following is the underlying cause of these findings?

A 50-year-old man comes to the physician because of an 8-month history of intermittent watery diarrhea and abdominal pain. He has had a 12-kg (26-lb) weight loss during this period. He has also had episodic pain of the ankle, wrist, and knee joints during the past 5 years. An endoscopy with small bowel biopsy is performed. Histopathologic examination of a tissue specimen shows foamy macrophages in the lamina propria with periodic acid-Schiff (PAS)-positive inclusions. Further evaluation is most likely to show which of the following?

A 45-year-old man comes to the emergency department because of a 1-day history of black, tarry stools. He has also had upper abdominal pain that occurs immediately after eating and a 4.4-kg (9.7-lb) weight loss in the past 6 months. He has no history of major medical illness but drinks 3 beers daily. His only medication is acetaminophen. He is a financial consultant and travels often for work. His partner had a positive urea breath test 2 weeks ago and was prescribed medication. Physical examination shows pallor and mild epigastric pain. Esophagogastroduodenoscopy shows a bleeding 15-mm ulcer in the antrum of the stomach. Which of the following is the strongest predisposing factor for this patient’s condition?

A 22-year-old woman comes to the emergency department because of chest and epigastric pain that started just after vomiting 30 minutes ago. She does not take any medications and does not drink alcohol or smoke cigarettes. While in the emergency department, the patient experiences two episodes of forceful, bloody emesis. Her temperature is 37.3°C (99.1°F), pulse is 110/minute, and blood pressure is 105/60 mm Hg. Physical examination shows dental enamel erosion and calluses on the dorsal aspect of her right hand. There is tenderness to palpation in the epigastrium. An x-ray of the chest is normal. Further evaluation of this patient is most likely to show which of the following findings?

A 45-year-old woman comes to the physician because of progressive difficulty swallowing solids and liquids over the past 4 months. She has lost 4 kg (9 lb) during this period. There is no history of serious illness. She emigrated to the US from Panama 7 years ago. She does not smoke cigarettes or drink alcohol. Cardiopulmonary examination shows a systolic murmur and an S3 gallop. A barium radiograph of the chest is shown. Endoscopic biopsy of the distal esophagus is most likely to show which of the following?

A 68-year-old man comes to the physician because of a 6-week history of episodic tremors, headaches, and sweating. During this time, he has gained 2.5-kg (5 lb 8 oz). Two months ago, he was diagnosed with type 2 diabetes mellitus and treatment with an oral antidiabetic drug was initiated. The beneficial effect of the drug that was prescribed for this patient is most likely due to inhibition of which of the following?

A 35-year-old woman comes to the physician because of a 3-month history of headache, palpitations, diarrhea, and weight loss. She takes no medications. Her pulse is 110/min and blood pressure is 125/70 mm Hg. Examination shows warm, moist skin and diffuse hyperreflexia. An MRI of the brain shows a sellar mass. The underlying cause of this patient’s condition is best explained by binding of a ligand to which of the following?

A 27-year-old man comes to the physician because of a 4-month history of recurrent episodes of headaches, palpitations, and sweating. He was adopted shortly after birth and does not know his biological parents. His pulse is 103/min and blood pressure is 160/105 mm Hg. Physical examination shows multiple soft, yellow papules on the tip of the tongue. There is a 2-cm, firm thyroid nodule. He has long and slender upper extremities, and his elbows and knees can be hyperextended. The most likely cause of this patient’s condition is a mutation in which of the following genes?

A previously healthy 44-year-old man comes to his physician because of frequent urination and increased thirst for several weeks. Physical examination shows darkened skin and a firm mass in the right upper quadrant. His blood glucose is 220 mg/dL. A photomicrograph of a specimen obtained on liver biopsy is shown. Which of the following best describes the pathogenesis of the disease process in this patient?

A 41-year-old woman comes to the physician because of a 1-year history of fatigue, irregular menstrual cycles, and recurrent sinus infections. Examination shows hirsutism and hypopigmented linear striations on the abdomen. Serum studies show hypernatremia, hypokalemia, and metabolic alkalosis. Midnight salivary cortisol concentration and 24-hour urinary cortisol concentration are increased. Serum ACTH is also elevated. High-dose dexamethasone does not suppress serum cortisol levels. Which of the following is the most likely underlying cause of this patient’s condition?

A 59-year-old man comes to the physician because of a 6-month history of numbness and burning sensation in his feet that is worse at rest. He has not been seen by a physician in several years. He is 178 cm (5 ft 10 in) tall and weighs 118 kg (260 lb); BMI is 37 kg/m2. Physical examination shows decreased sensation to pinprick, light touch, and vibration over the soles of both feet. Ankle jerk is 1+ bilaterally. His hemoglobin A1C concentration is 10.2%. Which of the following pathophysiological processes is most likely to be involved in this patient’s condition?

A 53-year-old man comes to the physician because of fatigue, recurrent diarrhea, and an 8-kg (17.6-lb) weight loss over the past 6 months. He has a 4-month history of recurrent blistering rashes on different parts of his body that grow and develop into pruritic, crusty lesions before resolving spontaneously. Physical examination shows scaly lesions in different phases of healing with central, bronze-colored induration around the mouth, perineum, and lower extremities. Laboratory studies show:

Abdominal ultrasonography shows a 3-cm, solid mass located in the upper abdomen. This patient’s mass is most likely derived from which of the following types of cells?

A 33-year-old man comes to the physician because of a 5-month history of increasing fatigue, recurrent nausea, intermittent lightheadedness, and a 4.1-kg (9.0-lb) weight loss. He was diagnosed with vitiligo 8 years ago. He does not take any medications. His blood pressure is 104/69 mm Hg. Examination of the skin shows multiple well-demarcated white patches on the trunk and extremities. The buccal mucosa appears darkened. One hour after administration of cosyntropin, his serum cortisol is 2.7 μg/dL. Compared with a healthy adult, which of the following sets of additional serum values is most likely in this patient?

A previously healthy 2-year-old boy is brought to the physician because of a 10-day history of unsteady gait, frequent falls, and twitching of the extremities. Physical examination shows bilateral saccadic eye movement in all directions and brief, involuntary muscle contractions of the trunk and limbs. There is an ill-defined, nontender mass in the upper right abdomen. He undergoes surgical resection of the tumor. Histopathologic examination of this mass is most likely to show which of the following?

Two days after undergoing an emergency laparotomy following a motor vehicle collision, a 37-year-old man has increased thirst. Examination shows dry mucous membranes and decreased skin turgor. A review of his chart shows his urine output to be in excess of his fluid intake. Laboratory studies show a serum sodium concentration of 151 mEq/L and urine osmolality of 110 mOsmol/kg H2O. One hour after the administration of desmopressin, the serum sodium concentration is 147 mEq/L and urine osmolality is 400 mOsmol/kg H2O. One week later, his laboratory values are within normal limits. This patient’s condition was most likely caused by damage to which of the following structures?

A 71-year-old man comes to the emergency department because of a 2-month history of severe muscle cramps and back pain. He says that he is homeless and has not visited a physician in the past 20 years. He is 183 cm (6 ft 0 in) tall and weighs 62 kg (137 lb); BMI is 18.5 kg/m2. His blood pressure is 154/88 mm Hg. Physical examination shows pallor, multiple cutaneous excoriations, and decreased sensation over the lower extremities. Serum studies show:

An x-ray of the spine shows alternating sclerotic and radiolucent bands in the lumbar and thoracic vertebral bodies. Which of the following is the most likely explanation for this patient’s findings?

A 28-year-old woman, gravida 1, para 0, at 10 weeks gestation comes to the physician for her first prenatal visit. Today, she feels well. She has no history of serious illness. Her pulse is 75/min and blood pressure is 110/74 mm Hg. Examination shows no abnormalities. Ultrasonography shows a pregnancy consistent in size with a 10-week gestation. Serum studies in this patient are most likely to show which of the following sets of laboratory values?

A 34-year-old woman comes to the physician because of a 3-month history of fatigue and a 4.5-kg (10-lb) weight loss despite eating more than usual. Her pulse is 115/min and blood pressure is 140/60 mm Hg. Physical examination shows warm, moist skin, and a diffuse, non-tender swelling over the anterior neck. Ophthalmologic examination shows swelling of the eyelids and proptosis bilaterally. Which of the following is the most likely cause of this patient’s symptoms?

A 38-year-old woman undergoes hemithyroidectomy for treatment of localized, well-differentiated papillary thyroid carcinoma. The lesion is removed with clear margins. However, during the surgery, a structure lying directly adjacent to the superior thyroid artery at the upper pole of the thyroid lobe is damaged. This patient is most likely to experience which of the following symptoms?

A 62-year-old woman with a history of hypertension and type 2 diabetes mellitus comes to the physician for a routine health maintenance examination. She has smoked 1 pack of cigarettes daily for the last 15 years. Current medications include glyburide and amlodipine. The physician prescribes a medication that decreases the production of mevalonate. Which of the following changes to the serum is most likely to develop as an adverse effect of the prescribed drug?

A 13-month-old boy is brought to the physician for a well-child examination. Physical examination shows hepatosplenomegaly. A venous blood sample obtained for routine screening tests is milky. After refrigeration, a creamy supernatant layer appears on top of the sample. Genetic analysis shows a mutation in the apolipoprotein C-II gene (APOC2) on chromosome 19. This patient is at greatest risk for developing which of the following complications?

A 58-year-old man comes to the physician because of a 3-month history of diffuse muscle pain, malaise, pain in both knees, recurrent episodes of abdominal and chest pain. He has also had a 5-kg (11-lb) weight loss over the past 4 months. Four years ago, he was diagnosed with chronic hepatitis B infection and was started on tenofovir. There are several ulcerations around the ankle and calves bilaterally. Perinuclear anti-neutrophil cytoplasmic antibodies are negative. Urinalysis shows proteinuria and hematuria. Muscle biopsy shows a transmural inflammation of the arterial wall with leukocytic infiltration and fibrinoid necrosis. Which of the following is the most likely diagnosis?

A 23-year-old man comes to the emergency department because of palpitations, dizziness, and substernal chest pain for three hours. The day prior, he was at a friend’s wedding, where he consumed seven glasses of wine. The patient appears diaphoretic. His pulse is 220/min and blood pressure is 120/84 mm Hg. Based on the patient’s findings on electrocardiography, the physician diagnoses atrial fibrillation with rapid ventricular response and administers verapamil for rate control. Ten minutes later, the patient is unresponsive and loses consciousness. Despite resuscitative efforts, the patient dies. Histopathologic examination of the heart at autopsy shows an accessory atrioventricular conduction pathway. Electrocardiography prior to the onset of this patient’s symptoms would most likely have shown which of the following findings?

A 47-year-old woman is admitted to the hospital because of a 2-week history of low-grade fever, fatigue, and a 3-kg (6.6-lb) weight loss. Her temperature is 38°C (100.4°F). Physical examination shows pallor and a cardiac murmur. Her serum creatinine is 1.8 mg/dL. Urinalysis shows red cell casts and 2+ protein. A CT scan of the abdomen with contrast shows no abnormalities. Despite appropriate medical therapy, the patient dies. A photograph of the heart taken during autopsy is shown. Which of the following is the most likely explanation for the laboratory findings in this patient?

A 60-year-old man comes to the emergency department because of a 2-day history of sharp chest pain and a nonproductive cough. The pain worsens with deep inspiration and improves when he leans forward. Three weeks ago, the patient was diagnosed with an ST-elevation myocardial infarction and underwent stent implantation of the right coronary artery. His temperature is 38.4°C (101.1°F) and blood pressure is 132/85 mm Hg. Cardiac auscultation shows a high-pitched scratching sound during expiration. An x-ray of the chest shows enlargement of the cardiac silhouette and a left-sided pleural effusion. Which of the following is the most likely underlying cause of this patient’s current condition?

A 72-year-old woman comes to the emergency department because of a 2-week history of worsening shortness of breath, lower extremity swelling, and a 3-kg (6.6-lb) weight gain. Crackles are heard on auscultation of the chest. Cardiac examination shows a dull, low-pitched early diastolic sound at the 5th left intercostal space that becomes louder in the left lateral decubitus position at end-expiration. Which of the following is the most likely cause of these auscultation findings?

A 30-year-old woman comes to the physician because of worsening fatigue and shortness of breath for the past 7 months. She emigrated from China 2 years ago. Cardiac examination shows a loud S1. Which of the following contributes most to this auscultation finding?

A 32-year-old man who recently emigrated from Colombia comes to the physician because of a 3-month history of shortness of breath and fatigue. Physical examination shows jugular venous distention and an additional late diastolic heart sound. Crackles are heard at the lung bases bilaterally. Cardiac catheterization is performed and left ventricular pressures are obtained. The left ventricular pressure-volume relationship compared to that of a healthy patient is shown. Which of the following is the most likely cause of this patient’s heart failure?

A 27-year-old man is brought to the emergency department 30 minutes after being shot in the abdomen during a violent altercation. His temperature is 36.5°C (97.7°F), pulse is 118/min and regular, and blood pressure is 88/65 mm Hg. Examination shows cool extremities. Abdominal examination shows a 2.5-cm entrance wound in the left upper quadrant at the midclavicular line, below the left costal margin. Focused ultrasound shows free fluid in the left upper quadrant. Which of the following sets of hemodynamic changes is most likely in this patient?

A 63-year-old woman comes to the physician because of a 6-month history of fatigue and shortness of breath on exertion in addition to a 1-month history of ankle swelling. She has a history of sleep apnea. Examination of the lower extremities shows bilateral pitting pedal and ankle edema. Cardiac examination shows a widely split S2 that varies with respiration. An ECG shows right bundle branch block. Which of the following is the most likely etiology of the patient’s lower extremity edema?

A 30-year-old man with Down syndrome is brought to the physician by his mother for the evaluation of fatigue. Physical examination shows bluish-colored lips and digital clubbing that were not present at his most recent examination. Right heart catheterization shows a right atrial pressure of 32 mmHg. Which of the following is most likely involved in the pathogenesis of this patient’s current condition?

A 6-month-old girl is brought to the emergency department because her lips turned blue for several minutes earlier during feeding. Her father reports that the patient had similar episodes while playing that resolved quickly. During the examination, she sits calmly in her father’s lap. When her ears are examined, the patient begins to cry and her lips and fingers begin to turn blue. Further evaluation of this patient is most likely to show which of the following?

A 5-day-old boy is brought to the emergency department by his mother because of a 2-day history of difficulty feeding and multiple episodes of his lips turning blue. He was born at home via spontaneous vaginal delivery and Apgar scores were 7 and 8 at 1 and 5 minutes, respectively. Physical examination shows grunting and moderate intercostal and subcostal retractions. Echocardiography shows a single vessel exiting from the heart. Which of the following is the most likely underlying cause of this patient’s condition?

A 57-year-old man with congestive heart failure comes to the physician for a follow-up examination. His last transthoracic echocardiogram showed an ejection fraction of 39%. His blood pressure is 148/92 mm Hg. Treatment with a drug that decreases serum concentrations of renin and angiotensin II is initiated. Which of the following mechanisms of action is most likely targeted by this drug?

A 28-year-old man comes to the physician because of a 2-week history of testicular swelling and dull lower abdominal discomfort. Physical examination shows a firm, nontender left testicular nodule. Ultrasonography of the scrotum shows a well-defined hypoechoic lesion of the left testicle. Serum studies show an elevated β-hCG concentration and a normal α-fetoprotein concentration. The patient undergoes a radical inguinal orchiectomy. Histopathologic examination of the surgical specimen shows a mixed germ cell tumor with invasion of adjacent lymphatic vessels. Further evaluation is most likely to show malignant cells in which of the following lymph node regions?

A 53-year-old woman comes to the physician because of increasing shortness of breath on exertion for 5 months. She reports that she can not climb more than 2 flights of stairs and she is no longer able to run her errands as usual. One year ago, she was diagnosed with triple-negative breast cancer. She underwent a right-sided modified radical mastectomy and adjuvant chemotherapy. Cardiac examination shows a laterally displaced point of maximal impulse. Coarse inspiratory crackles are heard in both lower lung fields. Echocardiography shows a left ventricular ejection fraction of 30%. The physician informs the patient that her symptoms are most likely due to an adverse effect of her chemotherapy. The drug most likely responsible for the patient’s current symptoms belongs to which of the following groups of agents?

A 66-year-old man with coronary artery disease and hypertension comes to the emergency department because of intermittent retrosternal chest pain, lightheadedness, and palpitations. He has smoked one pack of cigarettes daily for 39 years. His pulse is 140/min and irregularly irregular, respirations are 20/min, and blood pressure is 108/60 mm Hg. An ECG shows an irregular, narrow-complex tachycardia with absent P waves. A drug with which of the following mechanisms of action is most likely to be effective in the long-term prevention of embolic stroke in this patient?

A 9-year-old boy is brought to the emergency department by his mother because of painful swelling in his right knee that started after he collided with another player during a soccer game. He has no history of serious illness except for an episode of prolonged bleeding following a tooth extraction a few months ago. Physical examination shows marked tenderness and swelling of the right knee joint. There are multiple bruises on the lower extremities in various stages of healing. Laboratory studies show a platelet count of 235,000/mm3, partial thromboplastin time of 78 seconds, prothrombin time of 14 seconds, and bleeding time of 4 minutes (N = 2–7). Which of the following steps in coagulation is most likely directly affected by this patient’s condition?

Four days after admission to the hospital for severe dehydration due to profuse, bloody diarrhea, a 10-year-old boy is evaluated for decreased urine output. Physical examination shows generalized abdominal tenderness and numerous punctate, non-blanching macules on the trunk and extremities. Serum creatinine and urea nitrogen are elevated. A peripheral blood smear shows schistocytes. Which of the following sets of laboratory values is most likely in this patient?

A previously healthy 68-year-old woman is brought to the emergency department because of a 3-day history of nausea, anorexia, polyuria, and confusion. Her only medication is acetaminophen, which she takes daily for lower back pain that started 6 weeks ago. Physical examination shows conjunctival pallor. She is oriented to person but not to time or place. Laboratory studies show a hemoglobin concentration of 9.3 g/dL, a serum calcium concentration of 13.8 mg/dL, and a serum creatinine concentration of 2.1 mg/dL. Her erythrocyte sedimentation rate is 65 mm/h. Results of laboratory studies 3 months ago were within the reference ranges. Which of the following is the most likely underlying cause of this patient’s condition?

A 55-year-old man comes to the physician because of worsening fatigue and recurrent bleeding from his gums for 2 weeks. Physical examination shows marked pallor. There are scattered red, nonblanching pinpoint spots on his trunk and extremities. Laboratory studies show a hemoglobin of 8.0 g/dL, a leukocyte count of 80,000/mm3, and a platelet count of 104,000/mm3. Genetic analysis of a bone marrow aspirate shows leukemic cells with a balanced translocation between the long arms of chromosome 15 and 17. These cells are most likely to stain positive for which of the following?

A 34-year-old man comes to the physician because of blurry vision and fatigue for 2 months. During this period, he has also had occasional bleeding from his gums after brushing his teeth. One month ago, he was diagnosed with deep vein thrombosis after returning from an overseas business meeting. His pulse is 118/min, respirations are 19/min, and blood pressure is 149/91 mm Hg. Pulse oximetry on room air shows an oxygen saturation of 97%. Examination shows bluish discoloration of the lips. There is hepatosplenomegaly. Sensory examination of the hands shows paresthesia. Hemoglobin concentration is 18 g/dL, hematocrit is 65%, leukocytes are 15,000/μL, and platelets are 470,000/μL. His serum erythropoietin concentration is decreased. Activation of which of the following is the most likely underlying cause of this patient’s condition?

A 9-year-old boy is brought to the physician by his parents because of right-sided shoulder pain for 1 day. He has not had chills or sweating. At the age of 3 and 4, he was treated twice in the emergency department for painful swelling of his hands and feet. He emigrated with his family from Kenya 2 years ago. His temperature is 37.4°C (99.3°F), pulse is 96/min, and blood pressure is 123/82 mm Hg. Physical examination shows no tenderness, erythema, or joint swelling of the shoulder. Laboratory studies show:

A peripheral blood smear is most likely to show which of the following abnormalities?

An 8-year-old girl of Asian descent is brought to the physician because of fatigue. She is not able to keep up with the rest of her classmates in gym class because she tires easily. Physical examination shows pale conjunctivae. Laboratory studies show:

Peripheral blood smear shows small, pale red blood cells. Hemoglobin electrophoresis is normal. Which of the following is the most likely cause of this patient’s condition?

One day after delivery, a female newborn develops yellow discoloration of the eyes. She was born at term via uncomplicated vaginal delivery and weighed 3.4 kg (7 lb 8 oz). Her mother emigrated from Lesotho as a teenager. She did not receive prenatal care. Examination of the newborn shows scleral icterus and mild hepatosplenomegaly. Laboratory studies show:

Which of the following is the most likely cause of this patient’s condition?

A 3-year-old boy is brought to the pediatrician because of abdominal pain and constipation for 3 weeks. His mother says he has been increasingly irritable recently. His vocabulary consists of 50 words and he does not use sentences. Physical examination shows pale conjunctivae and abdominal tenderness. He refers to himself by name but is unable to name body parts or count to three. Peripheral blood smear shows small, pale red blood cells with basophilic stippling. Which of the following processes is most likely impaired in this patient?

A 39-year-old man comes to the physician for a follow-up examination. He was diagnosed with latent tuberculosis infection 3 months ago and has been taking his medication consistently. He has had generalized fatigue and dyspnea on exertion for the past 6 weeks. He does not smoke and drinks two to three beers on weekends. Vital signs are within normal limits. Examination shows conjunctival pallor. Laboratory studies show:

Which of the following is the most likely cause of this patient’s symptoms?

A 68-year-old woman comes to the physician for a follow-up examination. Three months ago, she underwent heart transplantation for restrictive cardiomyopathy and was started on transplant rejection prophylaxis. Her pulse is 76/min and blood pressure is 148/82 mm Hg. Physical examination shows enlargement of the gum tissue. There is a well-healed scar on her chest. Serum studies show hyperlipidemia. The physician recommends removing a drug that decreases T cell activation by inhibiting the transcription of interleukin-2 from the patient’s treatment regimen and replacing it with a different medication. Which of the following drugs is the most likely cause of the adverse effects seen in this patient?

A 17-year-old girl comes to the physician because of a sore throat, fevers, and fatigue for the past 3 weeks. Her temperature is 37.8°C (100°F), pulse is 97/min, and blood pressure is 90/60 mm Hg. Examination of the head and neck shows cervical lymphadenopathy, pharyngeal erythema, enlarged tonsils with exudates, and palatal petechiae. The spleen is palpated 2 cm below the left costal margin. Her leukocyte count is 14,100/mm3 with 54% lymphocytes (12% atypical lymphocytes). Results of a heterophile agglutination test are positive. This patient is at increased risk for which of the following conditions?

A 2-year-old boy with a history of multiple hospitalizations for fever and infection undergoes immunologic evaluation. Serum CH50 assay shows inappropriately low erythrocyte lysis and further workup confirms C8 deficiency. This patient is at increased risk for recurrent infections with which of the following pathogens?

A 3-month-old boy is brought to the physician by his parents because of a 2-day history of poor feeding and lethargy. He was born at term and has had three episodes of bilateral otitis media since birth. Umbilical cord separation occurred at the age of 8 weeks. He is at the 30th percentile for height and 20th percentile for weight. His temperature is 39.0°C (102.2°F) and blood pressure is 58/36 mm Hg. Physical examination shows white oral patches and confluent scaly erythematous skin lesions in the groin. Laboratory studies show a leukocyte count of 41,300/mm3 (92% segmented neutrophils and 8% lymphocytes) and a platelet count of 224,000/mm3. Blood cultures at 20°C (68°F) grow catalase-positive yeast cells. Which of the following is the most likely underlying cause of this patient’s symptoms?

An otherwise healthy 7-year-old boy is brought to the emergency department because of a 1-day history of involuntary muscle contractions and pain in his back and neck. Two weeks ago, he fell while playing in the sandbox and scraped his knees. He has not received any vaccinations since birth. His temperature is 38.5°C (101.3°F). He is diaphoretic. Examination shows inability to open his mouth beyond 1 cm. There is hyperextension of the lumbar spine and resistance to neck flexion. Administration of which of the following would most likely have prevented this patient’s current condition?

Twelve days after undergoing a cadaveric renal transplant for adult polycystic kidney disease, a 23-year-old man has pain in the right lower abdomen and generalized fatigue. During the past 4 days, he has had decreasing urinary output. Creatinine concentration was 2.3 mg/dL on the second postoperative day. Current medications include prednisone, cyclosporine, azathioprine, and enalapril. His temperature is 38°C (100.4°F), pulse is 103/min, and blood pressure is 168/98 mm Hg. Examination reveals tenderness to palpation on the graft site. Creatinine concentration is 4.3 mg/dL. A biopsy of the transplanted kidney shows tubulitis. C4d staining is negative. Which of the following is the most likely cause of this patient’s findings?

A 21-year-old man comes to the emergency department because of a 2-week history of progressive shortness of breath and intermittent cough with blood-tinged sputum. During this time, he has also noticed blood in his urine. He has no history of serious illness and does not take any medications. His temperature is 37°C (98.6°F), pulse is 92/min, respirations are 28/min, and blood pressure is 152/90 mm Hg. Cardiopulmonary examination shows crackles at both lung bases. Urinalysis is positive for blood and results of a direct enzyme-linked immunoassay are positive for anti-GBM antibodies. The pathogenesis of this patient’s disease is most similar to which of the following?

A 21-year-old woman comes to the physician because of a 1-week history of white discoloration of the tongue. She has had similar, recurrent episodes over the past 5 years. Examination shows white plaques on the tongue that easily scrape off and thick, cracked fingernails with white discoloration. KOH preparation of a tongue scraping shows budding yeasts with pseudohyphae. This patient’s condition is most likely caused by decreased activity of which of the following?

A 65-year-old man comes to his primary care physician for a routine health maintenance examination. He takes no medications. Physical examination and laboratory studies show no abnormalities. Compared to a healthy adolescent, this patient is most likely to have which of the following changes in immune function?

A 21-year-old woman comes to the physician because of a 5-day history of pain with urination and vaginal itching. She is sexually active with multiple partners and uses condoms inconsistently. Pelvic examination shows erythema of the vulva and vaginal mucosa, punctate hemorrhages on the cervix, and green-yellow, malodorous discharge. A photomicrograph of the discharge is shown. Which of the following is the most likely causal organism?

A 37-year-old man comes to the physician because of fever, night sweats, malaise, dyspnea, and a productive cough with bloody sputum for 4 days. He was diagnosed with HIV infection 15 years ago and has not been adherent with his medication regimen. Physical examination shows diminished breath sounds over the left lung fields. An x-ray of the chest shows an ill-defined lesion in the upper lobe of the left lung. A CT-guided biopsy of the lesion is performed; a photomicrograph of the biopsy specimen stained with mucicarmine is shown. Which of the following is the most likely causal organism?

A 46-year-old man comes to the physician because of a 1-week history of headache, muscle pain, and recurrent fever spikes that occur without a noticeable rhythm. Two weeks ago, he returned from a 5-week-long world trip, during which he climbed several mountains in India, Africa, and Appalachia. Chemoprophylaxis with chloroquine was initiated one week prior to the trip. Physical examination shows jaundice. The spleen is palpated 2 cm below the left costal margin. His hemoglobin concentration is 10 g/dL. A photomicrograph of a peripheral blood smear is shown. Which of the following agents is the most likely cause of this patient’s findings?

A 31-year-old man comes to the physician because of a 2-day history of abdominal pain and diarrhea. He reports that his stools are streaked with blood and mucus. He returned from a vacation in the Philippines 3 weeks ago. His vital signs are within normal limits. Abdominal examination shows hyperactive bowel sounds. A photomicrograph of a trichrome-stained wet mount of a stool specimen is shown. Which of the following organisms is the most likely cause of this patient’s symptoms?

A 28-year-old primigravid woman at 38 weeks’ gestation is brought to the emergency department in active labor. She has not had regular prenatal care. She has a history of HIV infection but is not currently on antiretroviral therapy. Her previous viral load is unknown. Treatment with intravenous zidovudine is begun to reduce perinatal transmission of the virus. Which of the following processes is most likely affected by this drug?

A 26-year-old man comes to the physician for a follow-up examination. He was diagnosed with HIV infection 2 weeks ago. His CD4+ T-lymphocyte count is 162/mm3. An interferon-gamma release assay is negative. Prophylactic treatment against which of the following pathogens is most appropriate at this time?

A 49-year-old man comes to the emergency department because of fatigue, cough, and worsening shortness of breath for 2 weeks. He is currently experiencing homelessness. He was diagnosed with HIV infection 25 years ago but has never had any symptoms. He has always refused to take antiretroviral medication. Pulmonary examination shows diffuse crackles over bilateral lower lung fields. An x-ray of the chest shows diffuse, symmetrical interstitial infiltrates. His serum level of beta-d-glucan is elevated. Further testing shows a heterozygous mutation that prevents entry of HIV into macrophages. Which of the following proteins is most likely affected by the mutation in this patient?

A 57-year-old man comes to the physician because of generalized malaise, yellowish discoloration of the eyes, and pruritus on the back of his hands that worsens when exposed to sunlight for the past several months. He has not seen a physician in 15 years. Physical examination shows scleral icterus and mild jaundice. There is a pruritic rash with several small vesicles and hyperpigmented lesions on the dorsum of both hands. The causal pathogen of this patient’s underlying condition was most likely acquired in which of the following ways?

A 35-year-old man comes to the physician because of an ulcer on his penis that he first noticed 4 days ago. He is currently sexually active with multiple male partners and uses condoms inconsistently. Genital examination shows a shallow, nontender ulcer with a smooth base and indurated border along the shaft of the penis. There is bilateral inguinal lymphadenopathy. Darkfield microscopy of a sample from the lesion shows gram-negative, spiral-shaped bacteria. A drug that acts by inhibition of which of the following is the most appropriate treatment for this patient?

A 27-year-old man comes to the emergency department because of nausea and repeated vomiting for the past 30 minutes. Two hours ago, he was at a summer barbecue gathering where he ate spicy, freshly grilled chicken that was fully cooked through with some reheated leftover lime basil rice. He has not had diarrhea. Physical examination shows a mildly tender abdomen with no rigidity or rebound tenderness. The next morning, his symptoms have resolved. Which of the following is the most likely cause of this patient’s symptoms?

A 23-year-old male comes to the physician because of a 2-week history of fatigue, muscle aches, and a dry cough. He has also had episodes of painful, bluish discoloration of the tips of his fingers, nose, and earlobes during this period. Three months ago, he joined the military and attended basic training in southern California. He does not smoke or use illicit drugs. His temperature is 37.8°C (100°F). Physical examination shows mildly pale conjunctivae and annular erythematous lesions with a dusky central area on the extensor surfaces of the lower extremities. Which of the following is the most likely causal organism?

A 7-year-old boy is brought to the physician by his mother because of low-grade fevers and a cough lasting for 2 weeks. He has vomited several times after fits of coughing. He has no history of serious illness and has not received any routine childhood vaccinations. His temperature is 38.3°C (101°F). Physical examination shows erythema of the nasal and oral mucosa. While in the exam room, he has a long series of consecutive coughs, during which he appears diaphoretic. The coughing is followed by a loud inspiratory gasp. Laboratory studies show a leukocyte count of 16,300/mm3 (67% lymphocytes). The pathogen most likely responsible for this patient’s presentation contains a toxin that acts by which of the following mechanisms?

A 55-year-old woman with type 2 diabetes mellitus is admitted to the hospital because of a 2-day history of fever, breathlessness, and cough productive of large quantities of green sputum. She drinks 8 beers daily. Her temperature is 39°C (102.2°F), pulse is 110/min, respirations are 28/min, and blood pressure is 100/60 mm Hg. Blood and sputum cultures grow gram-negative, catalase-positive, capsulated bacilli. Which of the following components of the causal organism is the most likely cause of this patient’s hypotension?

A 39-year-old man comes to the emergency department because of a 2-day history of fever, chills, dyspnea, and a non-bloody productive cough. He was diagnosed with HIV infection 4 years ago and has been on highly active antiretroviral therapy since then. His temperature is 38.8°C (101.8°F). Examination shows crackles over the left lower lung base. His CD4+ T-lymphocyte count is 520/mm3. An x-ray of the chest shows an infiltrate in the left lower lobe. Sputum cultures grow colonies with a narrow zone of green hemolysis without clearing on blood agar. The most likely causal pathogen of this patient’s condition produces which of the following virulence factors?

A 2-year-old boy is brought to the physician because of fever, productive cough, and shortness of breath. Since birth, he has had multiple respiratory infections requiring treatment with antibiotics. His immunizations are up-to-date. He is in the 10th percentile for height and weight. His temperature is 38.0°C (100.3°F). Examination detects diffuse bilateral wheezing and cervical lymphadenopathy. Flow cytometric analysis of a serum sample from the patient fails to fluoresce after incubation with dihydrorhodamine. This patient is at greatest risk of infection with which of the following organisms?

A 64-year-old woman comes to the emergency room because of a sudden weakness in her right arm and leg. She has atrial fibrillation, tinea unguium, gastroesophageal reflux disease, hypertension, and hypercholesterolemia. Current medications include warfarin, enalapril, simvastatin, lansoprazole, hydrochlorothiazide, griseofulvin, and ginkgo biloba. Two weeks ago, she had an appointment with her podiatrist. Physical examination shows sagging of her right lower face and decreased muscle strength in her right upper and lower extremity. Babinski sign is positive on the right. Her prothrombin time is 14 seconds (INR = 1.5). Which of the following drugs is the most likely underlying cause of this patient’s current condition?