What is causing these 2 pigmented lesions?

A 55-year-old female presented for evaluation of pigmented lesion on her thigh and was noted to have a dark area on 1 ankle. Both were asymptomatic. The lesion felt indurated like a nodule and when laterally compressed, it dimple slightly downward into the skin. The dark area on the ankle started in junior high and the spot on the thigh has been present for over a year. 

How would you diagnose the dark area on her ankle?

A. Becker’s nevus

B. Café-au-lait spot

C. Congenital nevus

D. Tinea nigra

E. Post-traumatic hyperpigmentation

What is causing the pigmented lesion on her thigh?

A. Compound nevus

B. Melanoma

C. Dysplastic nevus

D. Dermatofibroma

E. Pigmented basal cell carcinoma

(Answer and discussion on next page)

Answer: Becker’s nevus and dermatofibroma

The ankle hyperpigmentation is indicative of Becker’s nevus. It typically has onset at puberty and is more common in males. It is often associated with hypertrichosis. This benign condition can be confirmed by biopsy, but history with the clinical appearance is sufficient to make the diagnosis. 

The ankle lesion is diagnosed as dermatofibroma. This benign lesion is most commonly found on the lower extremities and is more common in women. No treatment is necessary.