The physiopathological significance of benign monoclonal gammopathy: a study of 64 cases.

Sixty-four patients with monoclonal protein in serum but initially without evidence of multiple myeloma, macroglobulinaemia, amyloidosis or lymphoma, were studied. Fifty patients (78%) were observed for a period of exceeding 3 years. Based on the follow-up data the patients were classified into the following four groups: Group 1 = patients with transient monoclonal gammopathy: 4 . 7%; Group 2 = patients without significant increase in monoclonal serum protein: 75%; Group 3 = patients with more than 50% increase in monoclonal serum protein: 14 . 1%; Group 4 = patients in whom multiple myeloma developed: 6 . 2%. The mean interval from discovery of the serum monoclonal protein to evolution to multiple myeloma was 61 months. Retrospective analysis of age, sex, blood count, bone marrow picture, antigenic type and size of serum monoclonal proteins, presence of small amounts of homogeneous light chain in the urine, serum albumin level, levels of residual immunoglobulins, did not help to distinguish initially the patients in whom the monoclonal gammopathy evolved to multiple myeloma from patients in whom the disease remained benign and stable. The evolution to multiple myeloma had occurred abruptly after long periods of stable condition; and until this progression the follow-up data were similar to the patients with benign disease. The possible physiopathology of occurrence and evolution of benign monoclonal gammopathy is discussed.