The laboratory diagnosis of plasma cell myeloma and related disorders.

Plasma cell myeloma constitutes the commonest primary malignant tumor affecting the skeleton of the adult. It is also one of several forms of monoclonal gammopathy that include Waldenström's macroglobulinemia, the heavy chain diseases, "benign" (nonprogressive, asymptomatic) monoclonal gammopathy, and primary amyloidosis. The diagnosis of classic or advanced myeloma rests on the findings of sheets of plasmacytic cells in a bone marrow biopsy sample or aspirate; a serum monoclonal immunoglobulin usually of the IgG or IgA class or Bence Jones protein in the urine; and evidence of multiple lytic lesions in x-ray views of the skeleton. Pitfalls in the diagnosis of earlier or unusual forms of myeloma require a careful application of classic diagnostic criteria or of criteria established by clinical cooperative groups.