μ‐heavy chain disease: Presentation as a benign monoclonal gammopathy

μ‐Heavy chain disease (HCD) is a rare monoclonal lymphoid disorder characterized by the failure to assemble a complete IgM immunoglobulin. The μ‐heavy chains analyzed to date revealed absence of the variable region and a shortened constant domain. We report the first case of μ‐HCD presenting as a benign monoclonal gammopathy. The literature on the 27 reported μ‐HCD cases is reviewed, and important clinical and laboratory findings are discussed. The ages of the patients ranged from 15 to 80 years (median, 57.5 years). Twenty‐two of 27 patients had an associated lymphoplasma cell proliferative disorder. A monoclonal spike on routine serum protein electrophoresis was found in only 8 of 19 patients. Fourteen of 22 patients had Bence Jones proteinuria, but μ‐HCD protein was reported in the urine of only two patients. The survival ranged from <1 month to 11 years (median, 24 months). © 1992 Wiley‐Liss, Inc.