Oncocytic nonsecretory multiple myeloma. A clinicopathologic study of a case and review of the literature.

We report on a morphologic variant of multiple myeloma, identified in a 39-year-old man, with osteolytic lesions in two ribs and three lumbar vertebrae. Serum electrophoresis was normal and immunofixation of serum and urine was negative. Histologic examination of a resected rib revealed a homogeneous population of neoplastic plasma cells with granular and eosinophilic cytoplasm. Immunohistochemical stains showed monoclonality for lambda light chain and negativity for all heavy chains. At the ultrastructural level, the cytoplasm of the neoplastic plasma cells was almost totally occupied by round and elongated mitochondria, pushing the rough endoplasmic reticulum to the periphery. To the best of our knowledge, only two similar cases have been reported in the literature so far. The usefulness of obtaining a clinicopathologic correlation for the behaviour of this extremely rare variant of multiple myeloma is discussed.