Cytoplasmic fibrils in plasma cells of a solitary myeloma.

A 56-year-old woman had solitary plasma-cell myeloma in the right humerus. Six weeks after local irradiation therapy, she died from pulmonary alveolar hemorrhage and bilateral pleural effusion with malignant plasma-cell infiltration of the right atrium. Ultrastructural studies of the plasma cells from the myocardium demonstrated large bundles of prominent, non-branching, solid cytoplasmic fibrils in many cells. Each fibril had a width of 66--132 A, periodicity of 30--60 A, and a beaded appearance. These features suggest that the fibrils may be protein material, possibly an immunoglobulin.