Primary Cutaneous Plasmacytoma
Primary extramedullary plasmacytoma is a rare plasma cell neoplasm that occurs as an isolated finding without detectable underlying multiple myeloma. Uncommonly, it has been reported to occur in the skin as a primary cutaneous plasmacytoma (PCP). The authors describe a case of an asymptomatic plaque on the back that was found to contain a monoclonal proliferation of plasma cells without evidence of systemic disease despite thorough evaluation. They also include a brief discussion of PCPs, including diagnosis and treatment.
The differential diagnosis includes cutaneous plasmacytoma occurring in the setting of systemic disease, and reactive polyclonal processes occurring in the setting of chronic infection or autoimmune disease. Possible treatment options include intralesional steroids, psoralen plus UVA, topical immunomodulators,10 local radiotherapy,11 and excision. Prognosis is varied, with reported cases showing complete remission, local recurrence, and progression to systemic disease, with the development of multiple myeloma in one-third of cases.4 More aggressive cases are associated with multiple lesions, larger size, and IgA secretion by neoplastic cells.
Our patient with a solitary dermal infiltrate of monoclonal plasma cells did not have bone marrow involvement and had an unexplained elevated level of free k light chains in the serum. This unexplained relationship underscores the importance of continued surveillance in any cutaneous lymphoma.
