A 6-year-old girl is brought to the office due to intermittent abdominal cramps, bloating, and diarrhea for 2 months.  She also has excessive flatulence, which typically occurs after meals.  The patient has had no fever or vomiting.  She eats a well-balanced diet and takes no medications or vitamins.  Vital signs are appropriate for age.  Examination shows a mildly distended abdomen with no hepatosplenomegaly or tenderness.  Laboratory evaluation reveals elevated tissue transglutaminase antibodies.  Which of the following locations should be biopsied to confirm the diagnosis in this patient?

Researchers studying gastrointestinal pathophysiology analyze hundreds of gastric mucosal biopsy specimens taken from patients who underwent endoscopy at a local tertiary care center.  They notice that colonization of the gastric antrum with S-shaped, gram-negative bacteria is associated with a decreased number of somatostatin-producing antral cells.  Depletion of these cells from the gastric antrum is most likely to cause which of the following conditions?

A 54-year-old man with a history of cirrhosis is brought to the emergency department by his wife, who found him agitated and confused.  She reports that he was nauseous and vomited bright red blood several times yesterday.  His cirrhosis is secondary to chronic hepatitis C infection, and he has received treatment for esophageal varices in the past.  Physical examination reveals abdominal distension, decreased liver span, and testicular atrophy.  A jerky, irregular flexion-extension tremor involving his hands is seen with wrist extension.  Which of the following is most likely to be elevated in this patient’s astrocytes?

A 44-year-old woman comes to the clinic after several near collisions over the past month while driving at night.  She also has generalized pruritus.  The patient has not seen a physician for several years and has missed several scheduled appointments.  She takes no medications.  On physical examination, she has patchy areas of coarse, thickened skin on the extremities.  Which of the following processes is most likely responsible for this patient’s findings?

A 53-year-old man comes to the office for routine follow-up after a total gastrectomy.  The patient was recently diagnosed with a gastric malignancy after several months of weight loss, fatigue, and anorexia.  He underwent an uncomplicated total gastrectomy and has had no postoperative complications.  This patient will require lifelong administration of which of the following substances?

A 15-year-old boy is brought to the clinic for a follow-up appointment.  Since early childhood, the boy has had recurrent episodes of pancreatitis requiring hospitalization.  The patient has not been hospitalized since before his last follow-up appointment a few months ago.  However, he has been feeling more tired recently and states he has not been taking his prescribed medications.  Family history is notable for recurrent pancreatitis in a sibling.  Neurologic examination shows hyporeflexia and decreased proprioception in the lower extremities.  Laboratory studies show mild hemolytic anemia.  This patient’s presentation is most likely due to a deficiency of which of the following?

A 70-year-old man comes to the office due to abdominal pain that began 1 month ago.  He has also experienced fatigue and weight loss.  He has no chronic medical conditions and takes no daily medications.  The patient worked in a factory that produced polyvinyl chloride for several decades and is now retired.  Physical examination shows hepatomegaly.  Imaging demonstrates a liver mass, which is subsequently resected.  Immunohistochemical staining of the tumor cells is positive for CD31.  Which of the following is the most likely diagnosis?

A 32-year-old man comes to the office due to a substernal burning sensation that has been occurring intermittently over the last 6 months.  The sensation worsens with spicy and fatty meals and is associated with food regurgitation and a sour taste in the back of the throat.  He has no projectile vomiting, dysphagia, or unexpected weight loss.  Medical history is significant for cystic fibrosis complicated by pancreatic insufficiency, for which the patient takes pancreatic enzyme replacement therapy with all meals.  Vital signs are within normal limits.  The abdomen is soft and nontender.  He is prescribed omeprazole with subsequent improvement in his gastroesophageal reflux symptoms.  In this patient, absorption of which of the following nutrients will likely improve due to initiation of this new medication?

A 16-year-old boy is brought to the emergency department due to severe retrosternal burning pain and odynophagia for the past 12 hours.  The patient has had no fever, sore throat, nausea, vomiting, or abdominal pain.  Medical history includes nodulocystic acne, for which he began taking oral doxycycline a week ago.  Vital signs are within normal limits.  Physical examination shows a normal oropharynx, clear lungs, normal heart sounds, and a nontender abdomen.  Upper gastrointestinal endoscopy reveals a small, punched-out ulcer in the proximal esophagus and normal-appearing gastroduodenal mucosa.  Doxycycline is presumed to be the culprit.  This medication most likely led to this patient’s current condition through which of the following mechanisms?

A 42-year-old man comes to the office due to increased abdominal girth associated with a 9-kg (19.8-lb) weight gain over the past month.  He drinks a liter of vodka daily and denies smoking or using intravenous drugs.  Blood pressure is 110/70 mm Hg.  The abdomen is moderately distended, and a fluid wave is elicited.  Multiple spider angiomas are present.  Laboratory studies reveal thrombocytopenia, hypoalbuminemia, a normal sodium level, and an elevated PT.  An upper endoscopy is performed, which shows no esophageal or gastric varices.  Pharmacotherapy aimed at inhibiting which of the following should be considered for this patient?

A 52-year-old man comes to the office due to diarrhea.  For the past 3 months, he has had loose, brown, watery stools 4 or 5 times a day; it is associated with postprandial bloating.  The patient has no vomiting, melena, hematochezia, or unexpected weight changes.  He was diagnosed 10 years ago with systemic sclerosis, which presented with sclerodactyly and Raynaud phenomenon.  The patient does not use tobacco, alcohol, or illicit drugs.  The abdomen is visibly distended but nontender and without rebound or guarding.  His symptoms dramatically improve after treatment with oral antibiotics.  Which of the following is most likely responsible for this patient’s diarrhea?

A 63-year-old man comes to the office due to intermittent rectal bleeding.  The bleeding worsens with defecation and is associated with itchiness.  Ten years ago, he had a kidney transplant for diabetic nephropathy and reports compliance with posttransplant immunosuppression medications.  Vital signs are normal.  Physical examination reveals a 2-cm ulcerated mass extending from the anal verge into the rectum.  Biopsy shows large, eosinophilic squamous epithelial cells arranged in islands; cells have hyperchromatic, irregular nuclei, and scant cytoplasm.  Significant keratinization is present.  Which of the following factors is most likely responsible for the development of this patient’s anal lesion?

A 6-year-old boy is brought to the emergency department due to abrupt-onset vomiting, lethargy, and altered mental status.  For 4 days, the patient has had a fever, cough, and rhinorrhea, which were treated symptomatically with aspirin.  He has no prior medical conditions, and his family history is unremarkable.  Vital signs are normal.  The patient is stuporous and does not respond to verbal commands.  Hepatomegaly is present.  There is no jaundice.  Laboratory results are as follows:

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

A 54-year-old man comes to the office for evaluation of chronic diarrhea and weight loss.  He has had bulky, foul-smelling stools for the past 8 months, which usually occur shortly after eating.  There have been no nocturnal bowel movements, and he denies fecal incontinence.  The patient also experiences dull, epigastric abdominal pain that is exacerbated by eating and unrelieved by antacids.  He drinks 6 or 7 beers a day but denies tobacco or illicit drug use.  Vital signs are within normal limits.  The abdomen is tender to palpation in the epigastrium without distension, rebound, or guarding.  Sudan staining of a fecal specimen is positive, and fecal occult blood testing is negative.  Blood testing reveals normal hemoglobin.  Which of the following pathophysiologic changes are most likely present in this patient?

A 17-year-old girl is brought to the office due to yellow eyes for the past day.  The patient has no other symptoms, including fever, rash, abdominal pain, vomiting, or diarrhea.  She has been preparing for her high school exit examination and has been quite stressed.  Temperature is 37.1 C (98.8 F), blood pressure is 110/78 mm Hg, pulse is 80/min, and respirations are 14/min.  Mild scleral icterus is present.  The abdomen is soft with no hepatosplenomegaly.  Serum laboratory results are as follows:

Two weeks after her examination, the patient’s symptoms resolve.  Repeat testing shows a total bilirubin concentration of 1.5 mg/dL.  Which of the following changes most likely contributed to this patient’s hyperbilirubinemia?

A 37-year-old man comes to the emergency department due to worsening fatigue and a prolonged history of abdominal pain.  He has had no surgeries and takes no medications.  Examination shows mucosal pallor and epigastric tenderness on deep palpation.  Blood samples are obtained for testing.  Laboratory results are as follows:

CT scan of the abdomen reveals atrophy of the pancreas with multiple calcifications.  A primary impairment in which of the following steps of cobalamin absorption is the most likely cause of this patient’s anemia?

A 34-year-old man with upper gastrointestinal bleeding is brought to the local emergency department by ambulance.  He was found in front of a grocery store after customers called emergency medical services.  The patient is unable to provide any information, but his medical records show a history of alcohol use disorder.  After undergoing emergency evaluation and appropriate resuscitation, his condition stabilizes.  Gastric lavage fluid initially contained blood but cleared quickly.  Upper endoscopy shows a linear mucosal tear at the gastroesophageal junction.  The process directly responsible for causing this patient’s mucosal tear will most likely result in which of the following acid-base disturbances?

A 68-year-old man comes to the office due to increased abdominal distension.  The patient was discharged from the hospital last week after an acute pulmonary embolism.  He also has a history of emphysema caused by extensive tobacco use.  The patient has no other medical conditions and does not use alcohol or illicit drugs.  Temperature is 37.6 C (99.7 F), blood pressure is 112/78 mm Hg, pulse is 85/min, and respirations are 18/min.  BMI is 27 kg/m².  Examination shows increased jugular venous pressure and lower extremity edema.  The abdomen is distended, and a fluid wave is present.  This patient’s ascites most likely developed due to which of the following changes in portal capillary exchange parameters?

A 60-year-old woman comes to the clinic for evaluation of fatigue and weakness.  A few months ago, she began feeling more tired than usual during the day.  The patient has also developed mild, intermittent abdominal discomfort.  Over the last few weeks, she has fallen down several times.  The patient has no known medical conditions and takes no medications.  Vital signs are normal.  Examination shows an ataxic gait.  The patient has hyporeflexia in the bilateral lower extremities, and there is loss of vibratory sensation.  Laboratory evaluation reveals anemia with evidence of hemolysis.  Peripheral smear reveals normocytic erythrocytes with normal segmentation of neutrophils.  Additional work-up confirms a micronutrient deficiency.  However, the patient says she consumes a well-balanced diet, and she has no dietary restrictions.  Which of the following is the most likely cause of this patient’s nutritional deficiency?

A 30-year-old man comes to the office due to a 4-month history of fatigue that is worse at the end of the day.  The patient has also had abdominal bloating and intermittent loose stools after meals.  His appetite is normal, and he has had no weight loss.  Vital signs are normal.  Examination shows pale mucosa.  The abdomen is mildly distended and tympanic; there is no tenderness or organomegaly.  Rectal examination reveals brown stool that is negative for fecal occult blood.  Laboratory results are as follows:

C-reactive protein level is normal.  Which of the following pathologic gastrointestinal tract findings is most likely to be present in this patient?

A 45-year-old woman comes to the office due to colicky abdominal pain, diarrhea, and nausea 15-20 minutes after meals.  These episodes are accompanied by light-headedness and diaphoresis.  She feels normal between the episodes and at night.  The patient underwent Roux-en-Y gastric bypass surgery 4 weeks ago for obesity.  She is otherwise healthy, and her only medication is a daily multivitamin.  On physical examination, the patient has a well-healed midline abdominal scar.  Mild epigastric tenderness to palpation is present.  The remainder of the examination is normal.  Which of the following is the most likely cause of this patient’s symptoms?

A 2-year-old boy with no chronic medical conditions is brought to the emergency department after he was found unresponsive with vomitus in his mouth.  The patient has had muscle aches, cough, rhinorrhea, diarrhea, vomiting, and fever for the past 3 days.  His parents gave him aspirin twice daily for symptom control.  Vital signs are within normal limits.  On examination, the patient is somnolent but withdraws from pain.  Pupils are equal in size and reactive to light.  Cardiopulmonary examination shows no abnormalities.  Hepatomegaly is present.  Extremities are well perfused.  Laboratory results are as follows:

Over the next day, the patient’s condition deteriorates and he dies despite supportive care.  Examination of the brain would most likely reveal which of the following findings?

A 54-year-old man comes to the office due to increasing pain in the right upper quadrant, nausea, and unintentional weight loss.  Vitals signs are within normal limits.  BMI is 21 kg/m².  The patient appears cachectic and there is scleral icterus.  The liver is palpable 3 cm below the right costal margin.  No ascites is present.  Laboratory studies reveal elevated bilirubin and alkaline phosphatase.  Contrast CT scan of the abdomen demonstrates moderately dilated right and left intrahepatic bile ducts, with a vague area of delayed enhancement at their convergence.  Biopsy of the lesion reveals columnar cells with hyperchromatic oval nuclei with prominent nucleoli arranged in glandular structures; mucin production with surrounding desmoplastic reaction is present.  Which of the following is the most likely diagnosis?

A 64-year-old woman comes to the emergency department due to a 2-day history of worsening abdominal pain.  She has a history of gallstones but has had no surgery due to high operative risk.  Medical history includes chronic obstructive pulmonary disease, hypertension, and remote cervical cancer treated with surgery and chemotherapy.  Abdominal CT scan shows multiple dilated small bowel loops with a decompressed distal ileum, and an abnormal bowel indicated by the arrow shown below:

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

An 18-month-old boy is brought to the office due to abnormal limb movements and delay in achieving motor milestones.  He is unable to pull up to stand or walk and recently developed stiffness in the extremities.  Birth history is remarkable for readmission at age 1 week for severe, persistent jaundice due to RhD incompatibility, which required intensive phototherapy and exchange transfusion.  On examination, the patient exhibits a limited upward gaze and dystonic extremity movement.  MRI of the head would most likely reveal abnormal signal in which of the following areas?

A 25-year-old woman comes to the office due to progressive fatigue and dizziness for several months.  She also has intermittent loose stools and abdominal cramps but no hematochezia, melena, vomiting, or abnormal menses.  Vital signs are within normal limits.  Conjunctival pallor is present.  The abdomen is mildly distended but nontender.  Laboratory evaluation reveals anemia and a low ferritin level.  Fecal occult blood testing is negative.  An upper endoscopy is performed and reveals no visible abnormalities of the stomach or duodenum, although biopsies of the duodenum are significant for intraepithelial lymphocytosis.  Which of the following is the most likely cause of this patient’s condition?

A 3-month-old boy is evaluated for fussiness and abdominal distension.  A contrast study is performed and shown in the image below:

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

A 70-year-old man comes to the office due to persistent epigastric discomfort and nausea for the past several months.  He has also noticed black-colored stools on several occasions.  Medical history is notable for hypertension and osteoarthritis.  The patient emigrated from rural China 5 years ago to live with his daughter.  He does not use tobacco, alcohol, or illicit drugs.  Physical examination shows a thin male with pale mucous membranes, an enlarged left supraclavicular lymph node, and epigastric tenderness on deep palpation.  Stool testing for occult blood is positive.  Upper gastrointestinal endoscopy reveals a 3-cm ulceration at the gastric antrum, with a heaped-up irregular border.  Biopsy from the edge of the ulcer reveals glandular structures containing intestinal-like columnar cells.  Which of the following most likely predisposed this patient to his current condition?

A 2-year-old girl is brought to the emergency department with intermittent pain in the abdomen that began several hours ago.  The patient also had a bowel movement that appeared tinged with blood.  Ultrasound shows an area along the ileum in which the proximal small intestine is telescoped into the distal small intestine.  Reduction via enema is unsuccessful, and the patient undergoes laparotomy with resultant resection of the involved intestine.  The pathologic finding at the lead point is shown in the exhibit.  Which of the following is the most likely underlying diagnosis in this patient?

A 1-month-old boy is brought to the office for follow-up of blood-streaked stools and diarrhea.  The patient was born preterm at 35 weeks gestation and had no complications in the newborn nursery.  He had been taking a standard cow’s milk–based formula until 2 weeks ago when he developed loose stools streaked with blood and mucus.  Symptoms resolved after changing the formula.  If histopathologic examination had been performed when the patient was symptomatic, which of the following would most likely be seen?

A 34-year-old woman is found dead in her apartment.  An autopsy examination is performed.  A ruptured plaque in the proximal anterior descending artery with an overlying occlusive thrombus is found.  Incidentally, a 4-cm hepatic mass in the right lobe of the liver is also found.  Grossly, the mass is well demarcated from the surrounding liver tissue and appears nodular with a central, gray-white, depressed stellate scar from which fibrous septa radiate to the periphery.  The rest of the liver is normal.  No additional abnormalities are noted on autopsy.  Which of the following is the most likely diagnosis of this patient’s liver lesion?

A 40-year-old woman comes to the office due to recurrent episodes of postprandial abdominal pain.  The pain is in the right upper quadrant and is associated with nausea.  The patient has no fever, jaundice, or loss of appetite.  Other medical conditions include obstructive sleep apnea and obesity.  The patient takes no medications.  She has never had any surgeries.  She does not use tobacco, alcohol, or illicit drugs.  The patient is afebrile.  Blood pressure is 140/90 mm Hg.  BMI is 38 kg/m².  Examination shows tenderness in the right upper quadrant.  Abdominal ultrasound demonstrates multiple gallstones.  A gross specimen obtained from laparoscopic cholecystectomy is shown in the image below:

A 45-year-old woman is brought to the emergency department with severe abdominal pain, fever, and confusion.  The patient’s husband reports that, yesterday, she began to have worsening right-sided abdominal pain associated with nausea and several episodes of vomiting.  This morning, she has been slow to respond and is confused about where she is.  The patient has a history of depression and takes sertraline.  Temperature is 39.5 C (103.1 F), blood pressure is 88/50 mm Hg, pulse is 104/min, and respirations are 26/min.  She appears ill and confused, and the sclera are icteric.  Abdominal examination demonstrates significant tenderness with guarding in the right upper quadrant.  Which of the following is the most likely underlying cause of this patient’s current condition?

A 4-day-old newborn is brought to the office for a 2-day history of progressive jaundice.  He was born at term following an uncomplicated vaginal delivery.  The patient has been breastfed since birth.  Vital signs are normal.  Examination shows scleral icterus and jaundice from the face to the upper abdomen.  Laboratory results are as follows:

Which of the following is the most likely explanation for these findings?