Enzymecytochemistry and immunohistochemistry in monoclonal gammopathy and reactive plasmacytosis.

Peripheral blood smears and bone-marrow smears from 29 patients with malignant M-components (25 with multiple myeloma and 4 with malignant lymphoma), 13 patients with benign monoclonal gammopathy (BMG), and 20 patients with polyclonal reactive plasmacytosis were examined by leucocyte alkaline phosphatase score (LAP-score) and by acid phosphatase score in plasma cells from bone-marrow smears. Furthermore, tissue sections from marrow biopsies from all patients were examined by the three-layer unlabelled immunoperoxidase technique to detect cytoplasmic immunoglobulin. The LAP-score was significantly higher in patients with malignant M-components than in patients with BMG and also higher in IgA and IgG myeloma than in IgA and IgG BMG, but the latter difference was not significant. Furthermore, a significant positive correlation between paraprotein concentration and LAP-score was found in multiple myeloma. Acid phosphatase score in plasma cells showed no clear distinction between multiple myeloma and BMG. Immunohistochemical examination showed a distinct monoclonal pattern in both multiple myeloma and BMG, allowing identification of the M-component which in all cases corresponded to the M-component detected by serum examination. Cells producing immunoglobulin classes not matching the M-component were more rare in multiple myeloma than in BMG, but the difference between the two conditions was quantitative and allowed no clear distinction.