Tinea Nigra: A Diagnostic Challenge – Hortaea Werneckii Infection Mimicking Acral Melanoma

Background: Tinea nigra is a rare, superficial mycosis caused by the dematiaceous fungus Hortaea werneckii, clinically characterized by hyperpigmented, non-scaly macules predominantly affecting palmar and plantar surfaces. Due to its melanized appearance, it is frequently misdiagnosed as acral lentiginous melanoma, leading to unnecessary invasive procedures. Objective: This article highlights the clinical, dermoscopic, and histopathological features of tinea nigra, emphasizing its differentiation from malignant melanoma to prevent misdiagnosis and overtreatment. Methods: A comprehensive literature review was conducted, analyzing documented cases of tinea nigra with emphasis on diagnostic pitfalls, potassium hydroxide (KOH) microscopy, fungal culture, and dermoscopic findings. Results: Tinea nigra presents as asymptomatic, brown-to-black macules with slight scaling, often solitary and asymmetrical. Dermoscopy reveals a "pigmented spicule" pattern without the blue-gray veil or irregular globules seen in melanoma. KOH preparation demonstrates septate hyphae and budding yeast cells, while histopathology shows pigmented fungal elements in the stratum corneum without melanocytic proliferation. Conclusion: Increased awareness of tinea nigra’s benign nature and distinctive diagnostic features is crucial to avoid confusion with melanoma, particularly in tropical and subtropical regions where H. werneckii is endemic.