HOW IS MGUS DISTINGUISHED FROM MYELOMA?
In patients with a plasma cell disorder and a circulating paraprotein, current practice is to subdivide these patients into three groups: MGUS, asymptomatic myeloma (previously termed smouldering, indolent or equivocal myeloma), and symptomatic myeloma. The distinction is important as it determines prognosis, and the need for treatment. Three variables define these groups: (1) M-protein level, (2) bone marrow plasma cell percentage, and (3) the presence or absence of myeloma related organ or tissue impairment (ROTI). The relevant investigations are therefore to estimate M-protein levels: serum protein electrophoresis, immunofixation and paraprotein quantification plus 24 h urinary light chain quantification. Bone marrow aspirate and trephine biopsy are also required to determine the extent of bone marrow infiltration. It should, however, be emphasised that while plasma cell percentage is part of the diagnostic criteria for MGUS, to avoid inappropriate over investigation bone marrow bio
