Neurotropic melanoma invading the median nerve.

We report a case of acral lentiginous melanoma of the right thumbnail bed which demonstrated characteristic intraneural invasion and extension along the median nerve. Four years after amputation of the involved thumb, a melanotic tumor recurred on the right thenar. Radiation therapy was given. The tumor invaded the median nerve, however, causing progressive pain and paralysis of the right hand. Despite right arm amputation, the tumor extensively metastasized, and the patient died three years later. Histopathologically, the tumors were characterized by extensive proliferation of spindle-shaped cells forming neuroid fascicles especially prominent in the metastatic region. Tumor cells were positive immunohistochemically with S-100 protein antisera.