Kaplan USMLE Step 3: Patient reports palpitations, nervousness

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 37-year-old accountant is hospitalized for a laparoscopic cholecystectomy. The day after his surgery, he reports feeling palpitations in his chest. He says that even prior to his hospitalization, he had been feeling nervous and has noticed himself perspiring more easily. His past medical history is significant for a resection of a benign brain tumor during childhood. He also mentions that he may have lost weight, although he has not been dieting.

Physical examination reveals a thin, anxious-appearing male. His lungs are clear, and cardiac auscultation shows an irregularly irregular rhythm with no murmurs. Neurologic examination is significant for a fine tremor in both hands. An electrocardiogram performed at the bedside shows atrial fibrillation.

Which of the following is the most appropriate next step in the workup of this patient?

A. Electrophysiology study

B. CT scan of the head

C. Cardiac stress test

D. Serum thyroid-stimulating hormone

E. Transthoracic echocardiography

The correct answer is D.

Nervousness, tremor, heat intolerance and weight loss are classic signs and symptoms of hyperthyroidism. Hyperthyroidism is a well known cause of atrial fibrillation. This arrhythmia will respond to the treatment of the underlying endocrine abnormality. A serum thyroid-stimulating hormone (serum TSH) level will be abnormally low in patients with hyperthyroidism and is a very specific test for this disorder.

Choice A. Electrophysiology studies assess the conduction system of the heart and are used to characterize arrhythmias, their location and the type of therapy required. Before an EPS, all reversible causes of arrhythmias (e.g., ischemia, an electrolyte imbalance) should be ruled out. In the present case, underlying hyperthyroid is clinically suspected on the basis of the patient's history.