Kaplan USMLE Step 1: After treatment, patient returns with new symptoms

If you’re preparing for the United States Medical Licensing Examination® (USMLE®) Step 1 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 36-year-old woman comes to the physician because of fatigue, weight loss, and nervousness. Treatment with methimazole is begun. Six weeks later, she returns to the physician because of a low-grade fever, arthralgias, and sore throat. Methimazole is discontinued immediately. Initial treatment measures for the patient's new symptoms should include a drug with which of the following mechanisms of action?

A. Granulocyte colony stimulation

B. Inhibition of the activity of peptidyltransferase

C. Inhibition of the enzyme thyroid peroxidase

D. Inhibition of reverse transcriptase

E. Inhibition of thyroid-hormone formation by interfering with the incorporation of iodine into tyrosyl residues of thyroglobulin

F. Stimulation of erythroid progenitor differentiation

The correct answer is A.

Fever and sore throat in a patient taking methimazole are concerning for agranulocytosis, a rare but serious side effect of methimazole therapy. Agranulocytosis is a severe lack of granulocytes (i.e., neutrophils, basophils, and eosinophils) and is most commonly drug-induced. The resulting neutropenia makes patients very susceptible to infection and treatment consists of a human granulocyte colony-stimulating factor to help stimulate the recovery of neutrophil counts.

Choice B. The most important steps in treating a patient on methimazole with fever are to stop the methimazole and address the presumed agranulocytosis. Inhibiting peptidyltransferase is an antibacterial mechanism of action that might be included in the treatment of this patient's infection but is not as essential as treating agranulocytosis.