Lymphomatoid papulosis, Ki-1+ lymphoma, and primary cutaneous Hodgkin's disease.

Lymphomatoid papulosis (LyP), Ki-1 lymphoma, and primary cutaneous, Hodgkin's disease (HD) appear to be histogenetically related disorders derived from activated T cells that express HD-associated antigens. Despite their morphologic and immunologic similarities, each disorder has a different clinical presentation and prognosis. LyP is associated with a long benign course of regressing papular lesions. The risk of developing a malignant lymphoma is approximately 10% to 20%. Ki-1 lymphoma, formerly known as regressing atypical histiocytosis (RAH), usually presents as one to several large lesions that can metastasize to regional lymph nodes. Single lesions can be treated by excision and local radiotherapy. Chemotherapy is necessary to control extracutaneous disease. Primary cutaneous HD probably does exist as a rare, often deep seated, nodular disorder that usually has a good prognosis. It should be distinguished from stage IV HD, which carries a grave prognosis. Evidence of associated nodal HD should be investigated in patients who present with skin lesions morphologically and immunologically indistinguishable from HD.