Benign Monoclonal Gammapathy (BMG)

Abstract

The term Idiopathic Paraproteinaemia or Benign Monoclonal Gammapathy (BMG) has been known to clinicians already for more than fourty years. It is used to denominate a condition characterized by the presence in serum of a homogeneous immunoglobulin (H-Ig) component persisting at a -more or less- constant concentration over many years, usually until the individual’s death (for a review see Radl, 1982). The concentration of such a H-lg component is usually less than 2 g/dl and the level of lg classes and subclasses other than those of the H-Ig may be normal or decreased but never to such an extent as seen in multiple myeloma (MM) or Waldenstrom’s macroglobulinaemia (WM). The class distribution of H-Ig is approximately 60%, 20% and 20% for IgG, IgA and IgM, respectively. Bence Jones proteinaemia and/or proteinuria, frequent in MM and WM, is very rare in BMG. When investigating the bone marrow cells, an increased monoclonal proliferation is found; however, these cells do not posses morphological abnormalities and they do not reach such a dominance as found in plasma cell malignancies. The benign character of this plasma cell proliferation is also reflected in the absence of bone destruction. The occurrence of BMG is clearly age-related: starting in the fourth decade, its frequency increases up to almost 20% in the tenth decade of life. The ratio of the incidence of malignant versus non-malignant monoclonal gammapathies (MG) can be estimated as about 1:200. Within the non-malignant MG, the BMG may represent about 50% of the cases.