Plasma cell acid phosphatase score in multiple myeloma and related disorders.

A detailed classification of plasma cells stained for acid phosphatase activity is introduced. With this method, patients with multiple myeloma, non-myeloma gammopathies, reactive plasmacytosis and other diseases in which plasma cells are involved, were investigated. The results show that our method can discriminate between multiple myeloma and reactive plasmacytosis. The overlap between multiple myeloma and other monoclonal gammopathies is much smaller than observed in other studies. Surprisingly low levels of acid phosphatase activity were found in the cells from patients with lymphoplasmacytoid immunocytoma. It is concluded that the acid phosphatase score can be of value for studying disorders in which plasma cells are involved.