Amelanotic acral melanoma mimicking a plantar wart.

Clinical presentation

An 80-year-old woman presented with a persistent painful lesion of the sole of her left foot. She treated it as a tyloma, with pumice stone abrasions and salicylic acid, for a few months. Physical examination found a 3- × 2-cm pinkish-yellow hyperkeratotic plaque resembling a viral plantar wart (Fig 1).

Fig 1

Clinical appearance. A 3- × 2-cm pinkish-yellow hyperkeratotic plaque with spots of subcorneal bleeding, resembling a viral plantar wart.

Dermoscopic appearance

Dermoscopy showed ill-defined milky-red areas, white-yellowish scales, thrombotic dotted vessels, and subcorneal hemorrhagic spots (Fig 2). The lesion was amelanotic, without residual pigmentation. Local treatments might have partially altered the dermoscopic appearance; repeated abrasions might have induced subcorneal bleeding and thrombosis of polymorphic vessels.

Fig 2

(A and B) Dermoscopy shows ill-defined milky-red areas (asterisk), white-yellowish scales, thrombotic dotted vessels (thin arrows), and subcorneal hemorrhagic spots (thick arrows).

Histopathologic findings

Histopathology findings showed a markedly atypical melanocytic proliferation of cells at the dermoepidermal junction and dermis, consistent with an invasive melanoma with a Breslow thickness of 0.4 mm (Fig 3). Tumor cells were positive for S100, Melan-A, and HMB-45 histochemical staining.

Fig 3

Histopathologic findings. Markedly atypical melanocytic proliferation of single cells at the dermoepidermal junction and in the dermis. (Hematoxylin-eosin stain; original magnification: ×4.)

Amelanotic acral melanoma is rare and often mimics calluses, warts, nonhealing ulcers, or nonmelanoma skin cancers. An accurate diagnosis tends to be delayed, leading to an unfavorable prognosis. A higher rate of amelanosis is reported in acral melanoma compared with other melanoma types. Diagnosis is challenging because of the absence of clinical diagnostic features routinely associated with melanomas, such as asymmetry, irregular borders, and color variegation. Dermoscopy can help identify in acral melanoma residual peripheral pigmentation (parallel ridges) and multicomponent pigmentation patterns. In amelanotic variants, the main dermoscopic features are milky red areas and polymorphous vessels. A biopsy should be taken of a solitary, longstanding, therapy-resistant acral lesion of unclear nature.