[Monoclonal gammopathy of undetermined significance : when and why to look for them ?].

Monoclonal gammopathy of undetermined significance (MGUS) is an asymptomatic premalignant plasma cell disorder. MGUS is a common disorder and the diagnosis is often made accidentally when a protein electrophoresis is performed in a routine blood test or during a biological assessment for other conditions. In the absence of biological abnormalities or clinical symptoms suggesting a plasma or lymphoplasma-cell disorder, there is no indication for routine screening of the monoclonal protein. When MGUS is diagnosed, the risk of transformation into myeloma or other lymphoproliferative disorders is estimated at 1 % per year. MGUS can also be associated with diseases that are not malignant disorders and in some cases, the monoclonal gammopathy is the witness of another rare but severe disorder wich will be critical not to be missdiagnosed.