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.

Key message.

Amelanotic acral melanoma is rare and often mimics calluses, warts, nonhealing ulcers, or nonmelanoma skin cancers.¹ 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.¹ Diagnosis is challenging because of the absence of clinical diagnostic features routinely associated with melanomas, such as asymmetry, irregular borders, and color variegation.¹ Dermoscopy can help identify in acral melanoma residual peripheral pigmentation (parallel ridges) and multicomponent pigmentation patterns.² In amelanotic variants, the main dermoscopic features are milky red areas and polymorphous vessels.¹ A biopsy should be taken of a solitary, longstanding, therapy-resistant acral lesion of unclear nature.

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.)