Clinical Features of Patients with a Serum M Component

The series comprised 169 patients with a serum M component (MC). Their mean age was 67.9 years. Eighty patients (47.3%) had a primary malignant lymphocytic or plasmacellular disease (68 myeloma, 6 macroglobulinaemia, 4 lymphoma, 2 chronic lymphocytic leukaemia). In 88 patients the MC was considered secondary and in one patient it was probably primary benign. In the group with a secondary MC the most common diagnoses were cardiovascular disease, an immunological disorder, infection, diabetes, and carcinoma. The possibility of a causal relation between cancer or prolonged antigenic stimulation and emergence of M components is discussed. Among 14 patients with definite myeloma the mean serum concentration of MC was 35.7 g/l, among 32 with secondary MC 12.9 g/l. Of the 68 patients with myeloma, 60% had an IgG MC, 22% an IgA MC and 18% an MC composed only of light chains. Of the patients in whom this paraprotein was secondary, it was IgG in 77%, IgA in 14% and IgM in 9%. One patient in this group had Bence Jones proteinuria; none had a pure light chain MC. Among patients with IgG or IgA myeloma or with a secondary MC and in whom the light chain type was identified, the kappa:lambda ratio was 1.5: 1. Of the 11 patients with demonstrated light chain myeloma, the MC was of the kappa type in 4 and of the lambda type in 7. The levels of “background” immunoglobulins were depressed in 88% of patients with a lymphocytic or plasmacellular neoplasia and in 38% with a secondary MC. Of the 91 patients whose serum samples were assayed for antibody activity, high titres were observed in 10.