A 25-year-old woman notices a slowly enlarging, asymptomatic, dark brown to black macule with irregular borders on the palm of her hand, present for one year. A dermatologist suspects acral lentiginous melanoma, but biopsy of the stratum corneum shows brown, septate, branching hyphae. The most likely diagnosis is:

• A Pityriasis versicolor caused by Malassezia furfur
• B Chromoblastomycosis caused by Fonsecaea pedrosoi
• C Tinea nigra caused by Hortaea werneckii ✓
• D Tinea corporis caused by Trichophyton rubrum

Explanation

Tinea nigra is a superficial infection of the stratum corneum of palms and soles caused by the dematiaceous fungus Hortaea werneckii (formerly Exophiala werneckii). It presents as a painless, dark macule that clinically mimics melanoma, making biopsy or scraping important; KOH shows pigmented septate hyphae without Medlar bodies or budding yeast clusters. Fonsecaea causes chromoblastomycosis, which involves the dermis with verrucous lesions and sclerotic bodies.

Reference: Fitzpatrick's Dermatology, 9th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.