USMLE Step 1 Question 321

Question:

A 19-year-old female college student presents to the student health center complaining of a sore throat and headache. She reports that she had been feeling tired and worn-down for the past few weeks, but attributed it to her busy schedule at school. She denies feeling sad or depressed and denies weight loss. On physical exam, she has enlarged posterior chain cervical lymph nodes. What histology is likely to be seen when the physician looks at her peripheral blood smear?

Correct Answer: B.  Atypical lymphocytes with clumped chromatin and irregular nuclei surrounded by normal RBCs

This patient has a classic presentation for mononucleosis secondary to infection with Epstein-Barr virus (EBV). The finding on peripheral blood smear is atypical lymphocytes with clumped chromatin and irregular nuclei. (choice B).

Choice A refers to a neoplastic process such as chronic myelogenous leukemia, in which all stages of granulocyte maturation can be in seen in the peripheral blood (as opposed to just the bone marrow). The typical patient would present with weight loss and diffuse lymphadenopathy, not focal. The mean age of onset is 50 years and it is slightly more common in men.

Knobs on RBC membranes and intrerythrocyte organisms, Choice C, describes the typical blood smear of a patient with malaria. Look for a history of recent travel in the patient history.

Microcytic, hypochromic red blood cells, Choice D, describes the typical smear for iron deficiency anemia. While possible in this case given the fatigue, it wouldn’t explain that lymphadenopathy or sore throat.

Microspherocytes, Choice E, are a classic finding on a peripheral blood smear in a patient with hereditary spherocytosis. Look for a family history of anemia.