A 72-year-old man is found to have pleural effusions on chest CT scan.  One year ago, he was diagnosed with advanced unresectable adenocarcinoma of the pancreas, which has progressed despite treatment.  Blood pressure is 108/60 mm Hg and pulse is 92/min.  BMI is 17 kg/m².  On physical examination, the patient is cachectic.  Neck veins are not distended and the trachea is central.  Lung auscultation reveals bibasilar decreased breath sounds with dullness to percussion.  There are no lung crackles.  Heart sounds are normal.  The abdomen is scaphoid with no tenderness.  There is bilateral lower extremity pitting edema.  Chest imaging reveals bilateral small to moderate sized pleural effusions.  Thoracentesis yields straw-colored fluid; laboratory results are as follows:

Serum total protein is 3.8 g/dL, and serum lactate dehydrogenase is 80 U/L.  Which of the following best explains this patient’s pleural effusions?

A 20-year-old, previously healthy man is brought to the emergency department due to acute onset epigastric pain, nausea, vomiting, photophobia, and blurry vision.  Several hours ago, he drank homemade alcohol at a friend’s party in a rural location.  Temperature is 36.7 C (98.1 F), blood pressure is 100/70 mm Hg, pulse is 88/min and regular, and respirations are 28/min and shallow.  The patient appears restless and confused.  Physical examination shows dilated pupils and sluggish pupillary reflex.  The abdomen is soft and nontender.  Laboratory results are as follows:

Accumulation of which of the following substances is most likely responsible for this patient’s visual symptoms?

Electrophysiologists conduct a study in which they record the membrane potential changes of cardiac pacemaker cells while exposing them to various agents.  A tracing from one of the experiments is shown below:

Which of the following substances is most likely responsible for the changes seen beginning at the point indicated by the arrow?

A 56-year-old woman comes to the office due to generalized muscle weakness and muscle cramps.  Medical history is significant for Sjögren syndrome, but she takes no medications.  Physical examination shows mild muscle weakness.  Laboratory results are as follows:

Which of the following best explains the laboratory findings in this patient?

A 72-year-old man is brought to the emergency department due to a 3-day history of fever, cough, and confusion.  Temperature is 38.9 C (102 F), blood pressure is 70/50 mm Hg, and pulse is 112/min.  On physical examination, the patient is lethargic but arousable.  Coarse rhonchi are present over the right lung base.  Chest x-ray reveals right lower lobe pneumonia.  The patient is admitted in the intensive care unit, and intravenous fluids and broad-spectrum antibiotics are begun.  In the hospital, the patient is noted to have low daily urine output measured from a urinary catheter.  On day 3 of hospitalization, his serum creatinine is 3.6 mg/dL; it was 2.2 mg/dL at admission.  The patient has no prior history of kidney disease.  A renal biopsy image representative of this patient’s disease process is shown in the exhibit.

Item 1 of 2

Which of the following is the most likely underlying cause of this patient’s acute kidney injury?

Item 2 of 2

The patient’s clinical condition gradually improves.  On day 7 of hospitalization, his serum creatinine level is 1.1 mg/dL.  Which of the following conditions would exhibit pathological kidney findings most similar to those observed in this patient?

A 24-year-old, healthy woman volunteers for an exercise research study.  In the study, various radiolabeled compounds are used to determine the source of skeletal muscle ATP during exercise.  The participants are given carbohydrate-rich food and are asked to run on a treadmill at high speed.  Which of the following is the most likely source of ATP represented by the red curve on the graph below?

A 43-year-old man is hospitalized due to severe epigastric pain radiating to his back.  He does not drink alcohol.  Temperature is 37.9 C (100.2 F), blood pressure is 114/68 mm Hg, and pulse is 85/min.  BMI is 34 kg/m².  The patient appears restless.  Physical examination shows significant epigastric tenderness.  Laboratory results are as follows:

Administration of intravenous fluids and analgesics is begun.  In addition, insulin is administered to rapidly reduce the elevated lipid levels.  This medication is likely to improve this patient’s condition by stimulating which of the following enzymes?

A 6-year-old girl is brought to the office by her mother due to abdominal pain.  The pain is diffuse and began this morning; it waxes and wanes in intensity.  The patient has had 2 episodes of nonbilious emesis.  She has had no fevers, sore throat, diarrhea, or bloody stools.  Two days ago, the patient developed an erythematous, macular rash over her legs and back that has become darker and more confluent today.  Blood pressure is 95/60 mm Hg.  The abdomen is soft and there is diffuse, mild tenderness on palpation with no rebound, guarding, or appreciable masses.  A raised, nonblanching rash is noted over the legs and back.  Urinalysis results are as follows:

Which of the following renal abnormalities is most likely to be present in this patient?

A 3-year-old boy is brought to the clinic due to fatigue.  A few weeks ago, the patient’s mother noticed that he seemed to tire easily after playing.  He also appeared pale.  The patient has had no recent illnesses and takes no medications.  Temperature is 37 C (98.6 F).  Examination shows mucosal pallor.  The abdomen is soft with no organomegaly.  The results of a complete blood count are as follows:

Peripheral smear shows microcytic, hypochromic erythrocytes.  The patient’s condition does not respond to a trial of iron therapy.  Further evaluation confirms the diagnosis, and the patient’s symptoms improve with pyridoxine (vitamin B₆).  This patient most likely has an underlying impairment in which of the following reactions?

A 54-year-old woman is evaluated in the clinic for exertional dyspnea and easy fatigability.  The patient has no chest pain, cough, or wheezing.  She does not use tobacco, alcohol, or recreational drugs.  On physical examination, her gait is unstable when her eyes are closed and there is impaired vibratory sensation in the lower extremities.  Marked pallor of the conjunctivae, nail beds, and palms is present.  Which of the following laboratory tests would help confirm the most likely diagnosis in this patient?

A 30-year-old woman comes to the office due to a facial rash for the past 3 weeks.  The rash worsens with sun exposure, and she has tried several topical sunscreens without relief.  The patient also reports easy fatigability and occasional pain and swelling of the hand joints.  Medical history is notable for mild cervical dysplasia that was diagnosed at age 21 and resolved spontaneously.  The patient does not use tobacco, alcohol, or recreational drugs.  Blood pressure is 140/85 mm Hg and pulse is 78/min.  Physical examination shows mucosal pallor, a superficial ulcer on the hard palate, and a rash as seen in the image below:

Cardiopulmonary and abdominal examinations are normal.  Which of the following laboratory findings is most likely to be seen in this patient’s condition?