A 22-year-old woman from coastal Kerala has a slowly enlarging, flat, brownish-black macule on the palm present for six months. It does not scale and cannot be scraped off. KOH mount shows dark brown, septate, branching hyphae. Culture grows a dematiaceous fungus. What is the causative organism?

• A Hortaea werneckii ✓
• B Piedraia hortae
• C Trichosporon asahii
• D Exophiala jeanselmei causing chromoblastomycosis

Explanation

Tinea nigra is a superficial infection of the stratum corneum of palms or soles caused by Hortaea werneckii, a dematiaceous fungus that produces asymptomatic brown to black macules mimicking acral melanocytic lesions. The KOH finding of pigmented hyphae confirms the diagnosis and spares the patient an unnecessary biopsy for melanoma. Piedraia hortae causes black piedra of scalp hair, and Trichosporon causes white piedra.

Reference: Rook's Textbook of Dermatology, 9th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.