Multiple myeloma with intramedullary masses of M-component.

The bone marrow of a patient with light chain myeloma and amyloidosis was substantially infiltrated with basophilic globular particles. The globules, which were confined to the bone marrow, ranged in size from tiny intracytoplasmic inclusions to large (100 mu) extracellular particles. Both the intra- and extracellular globules stained with fluorescent antibody directed against the light chain (kappa) produced by the patient's abnormal clone, and not with other fluorescent antiserums. By electron microscopy, even the largest extracytophasmic globules were bounded at least in part by rough membranes, suggesting that their extreme size was the result of cellular synthesis rather than extracellular coalescence.