Question of the Week

For August 14, 2018

A 57-year-old man presents with a one-year history of a frequent urge to move his legs, especially when lying down at night. The urge is usually accompanied by an unpleasant sensation in the legs that is relieved with leg movement. Sometimes these symptoms interfere with falling asleep, resulting in fatigue. The patient is otherwise well, and he takes no medications.

Physical examination is normal. Specifically, there is no muscle weakness or tenderness, and sensation in the legs is intact to light touch, position sense, vibration, and pinprick. Reflexes are 2+ and symmetric throughout. Cognition and affect are normal.

Serum creatinine, glucose, and electrolyte levels are normal.

What is the most appropriate next step in the laboratory evaluation of this patient’s symptoms?

Serum creatine kinase level
Liver function tests
Serum thyroid-stimulating hormone level
Serum vitamin B12 level
Serum ferritin level