A study of intracytoplasmic inclusions in myeloma cells from two patients with multiple myeloma.

Two cases of multiple myeloma which showed inclusions within the cytoplasma of myeloma cells were reported. One contained crystalline inclusions which were not stained by May-Grünwald and Giemsa, and the other contained Auer rod-like spindle shaped inclusions which were stained by May-Grünwald and Giemsa and PAS. Both cases were stained intensively by acid phosphatase but they were not stained by Congo red or by thioflavine-T. Moreover, they reacted only with anti-kappa sera in the immunofluorescent study and showed the same structure on electron microscopic observation. Although they showed different staining behaviors according to their compositions, they were considered to be essentially the same. It appears that light chains produced in excess are concentrated and form inclusions through the addition of sugar or digestion by lysosomal enzymes.