A Case of Tinea Nigra in Southern China

Tinea nigra, a rare superficial fungal infection caused by Hortaea werneckii, is often mistaken for a melanocytic lesion. We report a case in Shenzhen, a city in southern China, involving a 31-year-old woman with slowly enlarging brown patches on her left palm over 15 years. The patches were smooth, asymptomatic, and without scaling or travel history to tropical regions. Dermatological examination revealed a 30 mm × 25-mm brown macule with distinct borders. Dermoscopic analysis showed brownish-gray pigmented strands parallel to skin ridges, differing from the pattern in melanoma. Histopathological examination confirmed fungal hyphae in the upper stratum corneum. The fungus was identified as H. werneckii using metagenomic next-generation sequencing. The lesion resolved completely after an 8-week course of 1% butenafine cream. Accurate diagnosis is crucial to prevent misdiagnosis as malignant melanoma. Dermoscopy and fungal microscopy are key diagnostic tools. Treatment with topical antifungal agents is effective, with symptoms resolving within weeks.