USMLE Step 1 Question of the Week #6

6. A 48-year-old Japanese man presents to the clinic with multiple skin lesions as seen in the image:

He also complains of unintentional loss of weight even on a good diet and a healthy appetite. He denies smoking or alcohol abuse. On examination, the lesions are flat, velvety, hyperpigmented well defined lesions with a stuck-on appearance. The rest of the physical examination is unremarkable. Which of the following is the best investigation to be considered next in this patient?

QID#961