Abstract
RATIONALE: Subungual melanoma is the rarest subtype of cutaneous melanoma, accounting for approximately 1.9% of cases. Involvement of the fifth digit is exceptionally uncommon, often contributing to delayed diagnosis and poor outcomes. PATIENT CONCERNS: We report a case involving a 45-year-old male patient who presented with longitudinal melanonychia, a positive Hutchinson's sign, and ulceration of the nail plate on the right fifth finger. DIAGNOSES: Histopathological analysis confirmed subungual melanoma with a Breslow thickness of 4.3 mm. INTERVENTIONS: The patient underwent surgical amputation at the proximal interphalangeal joint, accompanied by a sentinel lymph node biopsy. The excised specimen demonstrated clear margins, and the sentinel lymph node biopsy was negative. Contrast-enhanced computed tomography of the chest, abdomen, and pelvis revealed no evidence of metastatic disease. OUTCOMES: At 2-month follow-up, the patient reported good wound healing and no evidence of recurrence, though he was subsequently lost to follow-up. This case highlights the diagnostic challenges of subungual melanoma, particularly in the fifth digit, and underscores the importance of maintaining a high index of suspicion for pigmented nail lesions. LESSONS: Early biopsy and timely surgical management remain critical for improving prognostic outcomes in rare presentations of melanoma.