Localized Diffuse Melanosis Associated With Melanoma Successfully Treated With Imiquimod Cream 5%: A Case Report and Review of the Literature

Diffuse melanosis associated with melanoma is a rare condition characterized by rapidly acquired skin pigmentation that usually occurs in the setting of advanced metastatic melanoma. We report a case of localized diffuse melanosis associated with melanoma on the lower left leg that successfully responded to treatment with imiquimod cream 5%. Initial treatment included application of imiquimod from the knee to the ankle once daily. Application frequency was increased to up to 3 times daily and eventually was switched to overnight occlusion until complete clearance was achieved.

This rare condition is not completely understood, as only approximately 20% of cases have shown individual melanoma metastases within the pigmented skin. In our patient, as in the majority of cases, we were unable to detect individual metastases within the pigmented skin. This case is unique because diffuse melanosis was confined to an extremity. The clearing of the pigmented skin was impressive. Imiquimod may have activity against melanoma, melanoma in situ, and diffuse melanosis associated with melanoma, as demonstrated in our case.