Dermoscopic features of acral lentiginous melanoma in a large series of 110 cases in a white population.

BACKGROUND: Acral lentiginous melanoma (ALM) is a rare but distinctive subtype of melanoma. The diagnosis is often delayed and misdiagnosis is common, due to frequently unusual clinical presentation and a higher rate of amelanosis than in other melanoma subtypes.

OBJECTIVES: We aimed to investigate the dermoscopic features of a large series of ALM in a white-skinned population, in order to emphasize their diagnostic value.

METHODS: All recorded dermoscopic photographs of ALM, including nail unit variants, were collected from the files of the University Hospital Department of Dermatology (Lyons, France) and reviewed.

RESULTS: In total 110 lesions, including 66 (60%) palmoplantar ALM and 44 (40%) ALM of the nail apparatus, were analysed for dermoscopic characteristics. The mean Breslow thickness was 2.6 mm. In volar skin melanomas, the two most prevalent patterns were irregular diffuse pigmentation (60%) and the parallel-ridge pattern (53%). Minor dermoscopic patterns, commonly noted in benign lesions, were also detected but only focally within the lesions. Among the 44 nail unit lesions, 31 (70%) presented irregular lines with variegations in colours, spacing, width and disruption of parallelism. Two cases of melanonychia striata had a triangular shape. Both corresponded to early ungual ALM. Association with subungual haemorrhage was not uncommon. The study included 37 (34%) amelanotic melanomas. However, dermoscopy enabled detection of microscopic remnants of pigmentation in most cases. The vascular pattern found in almost half of these lesions was polymorphous, with combinations of milky-red areas (95%), linear irregular vessels (49%), dotted vessels (43%) and hairpin vessels (41%).

CONCLUSIONS: The presence of a parallel-ridge pattern and/or irregular diffuse pigmentation within the lesion is highly indicative of melanoma on volar skin. An irregular lines pattern is the most prominent dermoscopic feature of pigmented ALM of the nail apparatus. Amelanotic ALM either in volar skin or in nail apparatus is characterized by remnants of pigmentation and a polymorphic vascular pattern.