In situ amelanotic melanoma of the nail unit mimicking lichen planus: report of 3 cases.

Background: Nail apparatus melanoma is known to be associated with a poor prognosis, mainly because of a delay in diagnosis that is made at an invasive stage. This delay is particularly true in cases involving amelanotic melanoma. To our knowledge, only 1 case of in situ amelanotic melanoma of the nail unit has previously been described. We report 3 cases of in situ amelanotic melanoma with clinical lichenoid features.

Observations: We describe 3 cases of in situ amelanotic melanoma of the nail unit. The patients ranged in age from 39 to 60 years. The lesions were located on the thumb (2 cases) or on the index finger (1 case). The duration of evolution was 6 to 18 months. Nail alterations were characterized by lichenoid changes with longitudinal striation, distal splitting, and nail plate atrophy. Histologic examination revealed in situ amelanotic melanoma extending from the proximal matrix up to the distal part of the nail bed. Complete excision of the nail apparatus was performed. There has been no sign of recurrence after follow-up of 1, 5, and 6 years.

Conclusions: Monodactylic lichenoid nail changes should be added to the more conventional signs of incipient nail melanoma. Chronic unexplained monodactylic nail dystrophy, especially in adults, should always be investigated histologically.