Monoclonal gammopathy of undetermined significance

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Monoclonal gammopathy of undetermined significance (MGUS, unknown or uncertain may be substituted for undertermined) is a condition in which a low or non-quantifiable level of a monoclonal paraprotein is detected in the blood by means of protein electrophoresis. It is generally benign with patients experiencing no ill health, but there is a very small risk (1-2% a year) that this might progress to multiple myeloma. In addition, some patients develop a polyneuropathy (damage to peripheral nerves) or other problems related to the secreted antibody.

Kyle et al studied the prevalence of myeloma in a population-wide cohort in Olmsted County, Minnesota. They found that the prevalence of MGUS was 3.2% in people above 50, with a slight male predominance (4.0% vs. 2.7%). Prevalence increased with age: of people over 70 up to 5.3% had MGUS, while in over-85's the prevalence was 7.5%. In the majority (63.5%) the paraprotein level was <1 g/dl, while only a very small group had levels over 2 g/dl.Kyle RA, Therneau TM, Rajkumar SV, Larson DR, Plevak MF, Offord JR, Dispenzieri A, Katzmann JA, Melton LJ 3rd. Prevalence of monoclonal gammopathy of undetermined significance. N Engl J Med 2006;354:1362-9. PMID 16571879.

The protein electrophoresis test should be repeated annually and if there is any concern for a rise in the level, then prompt referral to a haematologist is required. The haematologist, when first evaluating a case of MGUS, usually performs a skeletal survey (X-rays of the proximal skeleton), checks the blood for hypercalcemia and deterioration in the renal function and performs a bone marrow biopsy. If none of these tests are abnormal, a patient with MGUS is followed up once every 6 months to a year.

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