Follow-up Care of Monoclonal Gammopathy of Undetermined Significance: A Guide for Primary Care Physicians

Monoclonal Gammopathy of Undetermined Significance (MGUS) is a condition in which M protein, an abnormal monoclonal immunoglobulin, is present in the blood at a nonmalignant level. Specifically, it is defined by: blood serum M protein concentration <3 g/dL (<30 g/L), <10% plasma cells in the bone marrow, and no evidence of end organ damage [1,2]. Evidence of end organ damage includes hypercalcemia, renal insufficiency, anemia, and bone lesions. These are indicative of MGUS progression and which can be attributed to the monoclonal plasma cell proliferative process [3]. MGUS occurs in 3% of the general population older than 50 years. Incidence increases with age and varies with sex with higher rates observered in males than females [1,4]. MGUS is the most common plasma cell disorder, with 60% of patients that present to the Mayo Clinic with a monoclonal gammopathy being diagnosed with MGUS [3]. While it is typically an asymptomatic condition, it is premalignant disorder to other monoclonal gammopathies. Multiple Myeloma (MM) is almost always preceded by MGUS and the majority of patients will have detectable levels of M protein for at least 5 years prior to MM diagnosis [5,6]. MGUS also precedes immunoglobulin light chain (AL) amyloidosis and Waldenstrom Macroglobulinemia (WM) and tends to progress to disorders at a fixed but unrelenting rate of 1% per year [4].