Resident Rounds: Part III--Case Report: Metastatic Multiple Myeloma.

We report a case of cutaneous plasmacytomas developing in a patient with a 7-month history of progressive multiple myeloma refractory to bortezomib and combination chemotherapy. When involving the skin, plasmacytomas typically arise in the setting of multiple myeloma as contiguous extensions from underlying bony disease. More rarely, cutaneous plasmacytomas develop from hematologic metastases in patients with a high systemic plasma cell tumor burden. In our patient, the presence of cutaneous plasmacytomas involving two distinct sites, and malignant plasma cells within the dermis without infiltration into the subcutaneous fat, suggest a diagnosis of metastatic multiple myeloma to the skin. Metastatic multiple myeloma to the skin portends a poor prognosis, and treatment should be aimed at the underlying systemic disease.