Diagnosis

Discussion

Melanoma is one of the most common malignant skin tumor with wide ethnic variations. It has four common types namely, superficial spreading, nodular, lentigo maligna and acral lentiginous melanoma (ALM), with first one being most common type in white people. Of note, ALM is commonest in skin of color (Blacks, Asians, and Hispanics) accounting for 35–60% of melanomas having more advanced disease and poorer prognosis [1]. As the name suggests, it involves acral regions preferentially palms and soles. Elderly people are commonly affected and the incidence varies from 1 to 2 per million per year.

Aetiologically, occurrence of ALM has been attributed to some environmental triggering factors in genetically predisposed individuals. These external risk factors are trauma (especially burn and penetrating injuries), chemical exposure, tobacco use, pre-existing dysplastic nevi and malignant skin tumors [2]. Sunlight has no contribution unlike in other forms of melanoma. In most of the cases, mutations in BRAF, NRAS, MEK, ERK and wild-type KIT have been reported that lead to dysregulated mitogen-activated protein kinase (MAPK) pathway [3].

ALM was first described by RJ Reed in 1976 as pigmented lesions on the extremities, particularly on plantar regions characterized by an initial lentiginous/radial growth phase evolving with time to a late dermal/invasive phase [1]. Other common sites are palmar surface of the hands, fingers, toes and subungual region [4]. ALM usually starts with darkly pigmented blue-black macules (majority have >7 mm diameter) with irregular margins. Over the time, it becomes plaque with elevation of central area and at this stage, it is simulated by non-healing traumatic wounds, warts, chronic paronychia and pyogenic granulomas. Over months or years it evolves into tender nodules or exophytic lesions. Ulceration and bleeding are poor clinical prognostic signs.

Acral junctional nevus, talon noir and ulcerated lichen planus (LP) must be ruled out in all such cases. Acral junctional nevus potentially shares the clinical similarities, especially with early stage of ALM. It mostly presents as flat, dark brown macule with irregular border and of size usually ranging from 0.3 to 10 mm depending upon site and ethnicity of people [5]. It runs a benign course and histopathology is essential to rule out melanoma. Talon noir is one of the closest differentials of ALM which is caused due to traumatic rupture of dermal capillaries leading to intraepidermal haemorrhage. It presents as asymptomatic, bilaterally distributed violet-black macules on the heels, head of metatarsals, palms and fingers [6]. Paring reveals puncta of the black pigment of extravasated red cells confirming the diagnosis of talon noir. Ulcerative LP usually starts as erythema and bullae on the sole which runs a chronic and progressive course ultimately resulting in ulcers, scarring and deformities [7].