Melanosis in association with metastatic malignant melanoma - Report of a case and a unifying concept of pathogenesis

An unusual case of melanosis associated with metastatic malignant melanoma is reported. This was characterized by progressive blue/gray discoloration of the skin of the chest and abdomen in an elderly patient, 1 year after re moval of a polypoid malignant melanoma from the right arm. A biopsy of invo lved skin revealed perivascular aggregates of melanin-laden histiocytes thr oughout the dermis, the histopathologic hallmark of melanosis. An unusual a spect of the case was the coincidental finding of a tumor embolus within a small dermal vessel, probably a lymphatic. To date, neoplastic melanocytes have been detected in only a small minority of skin biopsies with features of melanosis. This case and a distillation of related information in the li terature lead to the conclusion that the essence of melanosis, and the feat ure that distinguishes this from conventional metastatic melanoma, is the p ersistent and cumulative dissemination of melanin, via the bloodstream, thr oughout the body. This in turn leads to progressive pigmentation of all int ernal organs and the skin. Only continuous access to the circulation by neo plastic melanocytes could explain such a phenomenon. Potential mechanisms b y which this could arise are discussed in the context of existing knowledge .