[Unexpected symptoms of monoclonal gammopathy].

Monoclonal gammopathy of undetermined significance (MGUS) is a common haematological disorder characterized by the presence of a monoclonal protein (M-protein). MGUS is considered an asymptomatic 'innocent' pre-malignant precursor condition of - mostly - multiple myeloma, without indication for treatment. We present three cases illustrating that MGUS can lead to serious problems. The first patient, a 51-year-old female, presented with polyneuropathy due to anti-MAG antibodies related to IgM MGUS. The second patient, a 37-year-old female, presented with proteinuria due to immunotactoid glomerulopathy caused by renal monoclonal IgG deposition associated with MGUS. The third patient, a 55-year-old female, presented with severe bleeding caused by an aspecific inhibitor of the coagulation cascade as part of IgG MGUS. In conclusion, in addition to the risk of progression to an overt haematological malignancy, MGUS can lead to severe symptoms and significant organ damage by auto-antibody activity or pathological accumulation in tissues of its toxic M-protein.