A 2-week-old girl in the neonatal intensive care unit for prematurity is evaluated for increasing episodes of apnea and bradycardia over the past 3 hours.  The patient was born at 29 weeks gestation via vaginal delivery; birth weight was 1.02 kg (2 lb 4 oz).  She has been receiving enteral feeds via nasogastric tube with premature formula.  Temperature is 36.1 C (97 F), blood pressure is 76/42 mm Hg, pulse is 150/min, and respirations are 44/min.  Pulse oximetry is 96% on room air.  The patient appears lethargic.  There is no cyanosis, stridor, or intercostal retractions.  The lungs are clear to auscultation bilaterally.  Heart sounds are normal with no gallops or heart murmur.  There is mild abdominal distension.  The extremities are well perfused.  Laboratory results are as follows:

Which of the following is the best next step in management?

A 1-year-old boy is admitted to the intensive care unit for severe respiratory distress and hypoxia requiring endotracheal intubation and mechanical ventilation.  Medical history shows 2 prior episodes of pneumonia, chronic thrush, and tympanostomy tube placement for recurrent otitis media.  His vaccinations are not fully up to date due to illness at the time of his well visits.  The patient is at the 2nd percentile for height and weight.  Physical examination shows diffuse crackles in both lungs.  Laboratory results are as follows:

Which of the following is the best long-term treatment for this patient?

A 10-hour-old boy in the newborn nursery has bilious emesis.  He was born at 38 weeks gestation by vaginal delivery to a primigravid 39-year-old woman who received no prenatal care.  The patient has voided once but has not yet passed meconium.  Physical examination shows a hypotonic neonate with a flat face, prominent tongue, low-set ears, and slanted palpebral fissures.  The hands are short with incurved fifth fingers, and a large space is present between bilateral first and second toes.  The abdomen is soft and without distension, guarding, or rigidity.  Auscultation reveals a loud holosystolic murmur most prominent at the left lower sternal border with a precordial thrill.  A nasogastric tube is placed, and abdominal x-ray is shown below.

In addition to echocardiogram, which of the following is the best next step in this patient?

A 3-year-old boy is brought to the clinic for evaluation of red-tinged urine, which his mother noticed earlier this week.  The patient has had multiple instances of blood-tinted urine but no associated dysuria.  He has had no prior injuries but was recently treated with antibiotics for streptococcal pharyngitis.  The patient has no chronic medical conditions and has reached all developmental milestones.  Temperature is 36.7 C (98.1 F).  Examination shows a well-appearing and well-nourished boy.  There is a firm, nontender, palpable mass in the left abdomen.  Results of urinalysis are as follows:

Which of the following is the most likely diagnosis for this patient?

A boy is brought to the nursery shortly after birth.  The patient was born at 36 weeks gestation to a 34-year-old primigravid woman via spontaneous vaginal delivery following a pregnancy complicated by chronic hypertension.  The only prenatal care was at 10 weeks gestation in the emergency department due to vaginal discharge and spotting.  At that visit, the mother’s blood pressure was 130/89 mm Hg.  BMI was 21 kg/m².  Ultrasound confirmed a 10-week intrauterine gestation.  The mother was diagnosed with Chlamydia trachomatis and treated with azithromycin.  The patient was born vigorous with Apgar scores of 7 and 9 at 1 and 5 minutes, respectively.  His measurements are charted in the image below, and the examination is otherwise unremarkable.

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

A 16-year-old boy is brought to the emergency department due to 3 weeks of progressive shortness of breath during physical activity.  The patient stopped playing golf 2 weeks ago after he became short of breath while walking the course.  He also feels more tired and weaker than usual.  The patient has had no rash, cough, chest pain, palpitations, dizziness, or fever.  His medical history is notable for sickle cell disease; he has had a few hospitalizations for pain crises and an episode of acute chest syndrome.  The most recent hospitalization was 6 months ago.  The patient’s only medication is oxycodone, which he takes intermittently for pain.  Temperature is 36.7 C (98.1 F), blood pressure is 120/70 mm Hg, pulse is 120/min, and respirations are 18/min.  Examination shows a tired-appearing but comfortable adolescent with conjunctival pallor.  Laboratory results reveal:

Which of the following is the most likely underlying mechanism for this patient’s laboratory findings?

A previously healthy 2-year-old girl is brought to the hospital due to lethargy and confusion for 1 day.  Four days ago, the patient developed fever and nasal discharge.  These symptoms resolved in 2 days, but she has been progressively tired and disoriented for the past day.  The patient’s older sister had a cold sore on her lip 2 weeks ago.  Temperature is 37.1 C (98.8 F).  On examination, she is minimally responsive.  The pupils are equal and have a sluggish reaction to light.  The sclerae are nonicteric, and the neck is supple.  Mild hepatomegaly is present.  Laboratory results are as follows:

CT scan of the head reveals diffuse cerebral edema.  Which of the following is most helpful to establish a diagnosis in this patient?

A 3-year-old boy is brought to the emergency department by his pregnant mother after developing severe abdominal pain within the past hour and having several episodes of vomiting.  The patient’s vomit is black and red in color.  Blood pressure is 80/50 mm Hg, pulse is 140/min, and respirations are 30/min.  On physical examination, he is irritable and lethargic.  Examination shows a normal oropharynx.  Cardiopulmonary examination is normal.  The abdomen is soft and mildly tender at the epigastrium; there is no hepatosplenomegaly.  The extremities are cool to the touch.  Laboratory results are as follows:

Chest x-ray is normal.  Abdominal imaging shows several radiopaque tablets in the stomach.  Intravenous normal saline is started.  Which of the following is the best next step in management of this patient?

A 4-month-old boy is brought to the emergency department after an episode of generalized tonic-clonic seizure 30 minutes ago.  The patient was born at 40 weeks gestation by spontaneous vaginal delivery.  He was at the 50th percentile for height and weight, and had a normal physical examination.  Since birth, the patient has had 3 episodes of upper respiratory infection and otitis media.  His parents and older sister have no medical problems.  On examination, the patient is lethargic.  He weighs 4.2 kg (9.3 lb, <5th percentile).  The anterior fontanelle is flat.  Pupils are reactive with normal fundi.  His tympanic membranes and pharynx are normal.  He has round cheeks and a doll-like face.  Heart sounds are normal without murmurs.  Lungs are clear.  The abdomen is protuberant and the liver is palpable 4 cm below the right costal margin.  Extremities are thin.  Laboratory results are as follows:

Urine dipstick is positive for ketones.  Serum triglyceride and uric acid levels are increased.  Which of the following is the most likely cause of this patient’s condition?

A 3-day-old boy is brought to the emergency department due to bruising.  The patient was born at 39 weeks gestation via vaginal delivery at home, and this is his first medical evaluation.  He is breastfed exclusively.  Vital signs are within normal limits.  Several ecchymoses are visible on the extremities.  Physical examination is otherwise unremarkable.  Laboratory results are as follows:

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

A 14-year-old girl is brought to the emergency department due to 5 weeks of progressively worsening left hip pain that is now making it difficult to walk up stairs.  She has also had intermittent fever and fatigue during this time.  The patient has no history of trauma and no chronic medical conditions.  Temperature is 38.3 C (100.9 F), blood pressure is 110/70 mm Hg, pulse is 88/min, and respirations are 18/min.  Examination shows swelling, tenderness, and warmth over the left iliac crest.  X-ray of the left hip demonstrates a radiolucent lesion in the left ilium with a layered periosteal reaction.  MRI is performed, and the results of biopsy of the left ilium are shown below.  Which of the following is the most likely diagnosis?

A 15-year-old boy is admitted to the hospital for management of right elbow pain and swelling.  The symptoms began 5 days ago while he was watching television at home.  The patient has factor VIII deficiency and has been receiving prophylactic recombinant factor VIII infusions through a subcutaneous port 3 times weekly since he was 11 months old.  When this episode began, the frequency of his infusions was increased to daily, but the swelling and pain remain.  Temperature is 37.6 C (99.7 F).  The right elbow has edema, is tender to palpation, and has limited range of motion relative to the left elbow.  Laboratory results are as follows:

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

A 17-year-old boy is brought to the clinic due to a breast mass.  He first noticed pain beneath his right nipple a month ago, and over the last few weeks, the right breast has become enlarged.  The patient has no chronic medical conditions and takes no medications.  He is doing well in school, and family history is unremarkable.  Height and weight are at the 75th percentile.  Temperature is 37 C (98.6 F), blood pressure is 110/66 mm Hg, pulse is 100/min, and respirations are 20/min.  Examination shows a prominent right breast with a palpable and tender, 5-cm, well-circumscribed mound deep to the right nipple.  There is no axillary or cervical lymphadenopathy.  Cardiopulmonary examination is unremarkable, and the abdomen is soft without tenderness.  Examination of the external genitalia shows testes without a palpable mass.  Sexual maturity rating (Tanner) is stage 5.  Laboratory results are as follows:

Which of the following is the best next step in evaluation of this patient?

A 12-year-old boy is brought to the office by his mother due to skin bruising, muscle aches, and fatigue.  She is concerned that these symptoms are due to him being bullied at school, which the boy denies.  He has also had significant nausea over the last week but has maintained adequate oral intake.  The patient has no chronic medical conditions.  Examination reveals mucosal pallor and numerous ecchymoses on the bilateral extremities.  Laboratory results are as follows:

Peripheral blood smear reveals significant immature myeloid cells.  Which of the following is the most likely underlying cause of this patient’s acute renal failure?