A 74-year-old Chinese male patient presented to the dermatology outpatient clinic with a 1-year history of distal onycholysis involving the left thumbnail. He had no family history of melanoma or other skin cancers. He denied any history of trauma to the affected digit. The lesion initially manifested as partial distal onycholysis of the left thumbnail (Fig. 1A). The patient received repeated manicure treatments at a nail salon for one year and was misdiagnosed with onychomycosis. After debridement of the detached nail plate, pale-red proliferative lesions with erosion were visible beneath the nail plate (Fig. 1B). The patient subsequently presented to our dermatology clinic for definitive diagnosis. Physical examination demonstrated partial defect of the distal nail plate, along with nail dystrophy and disappearance of the lunula at the affected area (Fig. 1C). No axillary lymph node enlargement was detected on examination. Biopsy results of the nail bed revealed proliferative atypical melanocytes with marked cellular atypia in both the epidermis and dermis (Fig. 1D). Immunohistochemical staining demonstrated that the tumor cells were positive for Melan-A, HMB45, and Prame, with a high Ki-67 proliferation index. The final diagnosis was subungual amelanotic melanoma. Subungual melanoma occurs significantly more frequently in dark-skinned Asian and African populations, accounting for 10%–25% of all melanoma cases. It is a rare subtype among Caucasians, with a proportion of only 1%–3%[
1–
3]. Subungual melanoma typically presents as longitudinal melanonychia or pigmented masses, and rarely manifests as onycholysis or non-pigmented masses. Early diagnosis of subungual amelanotic melanoma is challenging for dermatologists owing to the absence of pigment. Non-pigmented (amelanotic) subungual melanoma is often misdiagnosed as onychomycosis, warts, pyogenic granuloma, nail dystrophy, or squamous cell carcinoma. This case reminds clinicians that persistent, unresolving, and isolated onycholysis or amelanotic proliferative lesions require timely histopathological evaluation to confirm the diagnosis. No imaging evidence of metastasis was detected. The patient underwent wide local excision combined with sentinel lymph node biopsy (SLNB). SLNB was negative. He was ultimately diagnosed with American Joint Committee on Cancer (AJCC) stage IIIC (T3bN1cM0) acral melanoma, according to the AJCC 8th edition[
4]. Combination therapy with interferon α1b and toripalimab was initiated. Six months of treatment and regular follow-up were completed following the initiation of postoperative adjuvant therapy, and no local recurrence or distant metastasis was detected.
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