Tinea Nigra

A previously healthy 13-year-old girl presented with a 1-year history of a gradually enlarging light-brown spot on her left palm. Initially, she was evaluated by a dermatologist who suspected hyperpigmentation and prescribed hydroquinone cream. However, 2 weeks later, the pigmentation darkened, prompting concern for melanoma, and the patient was referred for further evaluation. The patient, a right-handed student, reported no recent travel history. Physical examination revealed a well-defined, non-scaling, brown, leaf-shaped patch on the left palm (Figure 1A). Dermoscopy revealed reticular pigmentation with thin bundles of brown spicules, distinct from the palmar furrows (Figure 1B). Palmar skin scrapings and histopathology confirmed the diagnosis of tinea nigra (Figure 1C, Figure S1). Tinea nigra is a rare superficial fungal infection, predominantly caused by Hortaea werneckii, often misdiagnosed due to its resemblance to melanocytic lesions [1], such as melanoma. Tinea nigra can mimic malignant melanoma in lesion color and growth, making differentiation crucial. Dermoscopy and mycological testing aid diagnosis: malignant melanoma typically shows asymmetrical colors, whereas tinea nigra presents thin reticulated lines on a homogeneous light-brown background [2], with superficial mycosis confirmed by mycological examination. The key dermoscopic feature of tinea nigra is the parallel ridge pattern, a malignant sign suggestive of acral-lentiginous melanoma, which is characterized by relatively hypopigmented furrows with asymmetrical structures and colors. However, tinea nigra often shows variable findings, with dots and pigmented spicules arranged in parallel and curvilinear lines, creating a reticular-like pattern. Unlike acral melanocytic lesions, pigmentation in tinea nigra does not follow the dermatoglyphic ridges and furrows of volar skin [1, 3, 4]. After treatment with topical clotrimazole, the patient's symptoms abated at 1-month follow-up (Figure S2). The authors declare no conflicts of interest. The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions. Figure S1: The immunohistochemical staining for Melan-A, demonstrating normal expression of melanocytes in the basal layer of the epidermis. Figure S2: The clinical appearance after four weeks of treatment. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.