Abstract

Multiple myeloma (MM) is a plasma cell malignancy that presents with systemic symptoms of hypercalcemia, renal disease, anemia, and lytic bone lesions. Cutaneous involvement of MM is extremely rare and manifests in less than 1% of cases.¹ In patients with an established diagnosis of MM, it typically occurs later in the disease course as hematologic metastasis or as a direct extension from underlying osteolytic lesions.¹ Uncommonly, cutaneous involvement can be an initial presentation of MM without any associated symptoms. A 64-year-old, otherwise healthy man presented with the cystic lesion in the right axilla. Skin examination showed a non-tender mobile subcutaneous nodule in the right axilla along with an erythematous papule on the anterior neck. Excisional biopsies of both lesions demonstrated nodular proliferations comprised of atypical cells with eccentrically located nuclei and “clock-face” chromatin. By immunohistochemistry, the cells exhibited CD138 and CD79a positivity with lambda restriction, consistent with plasmacytomas. Patient’s serum protein electrophoresis revealed an M-spike in the beta globulin region, further confirmed as IgA lambda by immunofixation electrophoresis.  A subsequent positron emission tomography-computed tomography scan (PET-CT) demonstrated hypermetabolic infiltration of multiple organs, including bones, lungs, and lymph nodes. Bone marrow biopsy showed plasma cell infiltration, confirming a diagnosis of MM. There is a paucity of reports of cutaneous involvement by MM at the time of diagnosis, and this presentation unfortunately portends a poor prognosis.^1-4 We report a potentially unique cutaneous presentation of MM clinically masquerading as a cyst.