What is this changing pigmented lesion?

A 44-year-old man presents for evaluation of a changing pigmented lesion on his trunk. What does this look like to you?

A. Pigmented basal cell carcinoma.
B. Malignant melanoma.
C. Dysplastic nevus.
D. Benign nevus.
E. Irritated seborrheic keratosis.

Answer and discussion on next page.

ANSWER: Dysplastic nevus

Given the age of the patient, and the appearance and location of the lesion, all the options in the differential are reasonable. A small biopsy—either punch or incisional—is sufficient to provide enough information for an appropriate course of action. This patient’s lesion proved to be a moderately dysplastic nevus, C, which was reexcised.

If time and facilities are limited, a deep shave biopsy may be performed—taking care to ensure the biopsy is deep enough to be under the lesion. Although complete excision with narrow margins will establish the diagnosis, this procedure can be considered unnecessarily extensive for a potentially benign lesion. Excision with wide margins is excessive before a definitive diagnosis is made.