Kaplan USMLE Step 3: 45-year-old reports four days of abdominal pain

If you’re preparing for the United States Medical Licensing Examination® (USMLE®) Step 3 exam, you might want to know which questions are most often missed by test-prep takers. Check out this example from Kaplan Medical, and read an expert explanation of the answer. Also check out all posts in this series.

A 45-year-old woman presents to the emergency room because of general malaise. She has been having abdominal pain for the past four days, associated with some nausea, vomiting and diarrhea. She has had a low-grade fever as well. Her husband brings her in because she has been slightly confused over the past few hours. She is otherwise healthy and does not take any medications. On physical examination she appears slightly somnolent but arousable. Her temperature is 37.9 ºC (100.3 ºF), and heart rate is 95 beats/min. She is saturating 99% on room air. Head and neck exam reveals mild scleral icterus. No lymphadenopathy is observed. Her chest is clear, and she is tachycardic. Her abdomen is mildly tender, but she does not demonstrate any guarding or rigidity. She has poor skin turgor, and she has no clubbing, cyanosis, or edema, although she appears pale. She is hemoccult-negative on rectal examination. Laboratory data:

• White blood cells: 9,200/mm³
• Hematocrit: 25%
• Platelets: 25,000/mm³
• Sodium: 137 mEq/L
• Potassium: 4.8 mEq/L
• Chloride: 103 mEq/L
• Bicarbonate: 21 mEq/L
• Urea nitrogen: 22 mg/dL
• Creatinine: 1.8 mg/dL
• Total bilirubin: 3.2 mg/dL
• Conjugated bilirubin: 0.8 mg/dL
• LDH: 400 U/L
• Peripheral blood smear: multiple fragmented red blood cells

Which of the following is the treatment of choice for this condition?

A. Corticosteroids

B. Plasma exchange therapy

C. Plasma transfusion

D. Platelet transfusion

E. Supportive treatment

The correct answer is B.

This patient has a clinical presentation concerning for thrombotic thrombocytopenic purpura (TTP), a rare entity that is characterized by a microangiopathic hemolytic anemia and thrombocytopenia, most importantly. There is a wide range of clinical entities that may present with this combination; however, high clinical suspicion and prompt treatment are warranted if TTP is suspected, as the disease is nearly uniformly fatal if left untreated. The classical pentad comprises fever, renal failure and neurologic findings. However, not all of these need be present for the diagnosis to be made and for treatment to be initiated. The treatment that has turned the prognosis of this disease around is plasma exchange therapy, whereby a patient's plasma is filtered and replaced with fresh frozen plasma.

Choice A. Corticosteroids are frequently used in conjunction with plasma exchange therapy; however, no randomized clinical trials have proven their benefit. Given a choice between corticosteroids and plasma exchange, the latter should be chosen.