What is the cause of this patient’s unilateral foot lesion?

David L. Kaplan, MD—Series Editor

pigmented lesion

This 15-year-old girl presented for evaluation of a new, pigmented lesion on 1 sole of at least 1 month’s duration that was asymptomatic. She spends a lot of time outdoors riding horses and was otherwise healthy.

What is the cause of this patient’s unilateral foot lesion?

A. Melanoma
B. Dysplastic nevus
C. Benign acral nevus
D. Lentigo
E. Fungal infection

Answer on next page.

pigmented lesion

Answer: Dematiaceous fungal infection

The KOH examination of this patient was positive, confirming the diagnosis of a dematiaceous fungal infection, or black mold. More than 100 species and 60 genera of dematiaceous, or pigmented, fungi have been implicated in human disease. The distinguishing characteristic common to all these various species is the presence of melanin in the cell walls, which imparts the dark color to their conidia or spores and hyphae.

Dematiaceous fungi generally are found in soil or associated with plants and are distributed worldwide. Fortunately, these organisms typically respond to topical azole or allylamine antifungals, as did the infection in this girl’s case. Dematiaceous fungal infection often is confused with melanoma, dysplastic nevus, benign acral nevus, lentigo, and other conditions because of the presence of melanin, and often a biopsy is performed to acquire the correct diagnosis.