Monoclonal Gammopathy Of Unknown Significance Incidence

MGUS indicates the presence of a monoclonal protein (M-protein) in persons without evidence of MM, macroglobulinemia, amyloidosis (AL), or related plasma cell disorders. MGUS can be associated with other disorders, including lymphoproliferative diseases, leukemia, connective tissue disorders, dermatologic diseases, and neurologic disorders.23 MGUS is found in approximately 3% of persons older than 70 years and in about 1% of those older than 50 years. In the largest series of MGUS patients published to date that included 1384 patients from Mayo Clinic from 1960 through 1994, the risk of progression to MM was 1% per year. Patients were at risk of progression even after more than 25 years of a stable monoclonal gammopa-thy. The risk of developing MM was 25-fold higher when compared with a similar population (from SEER database). The concentration of the serum M-protein was the major independent predictor of progression. Patients with an immunoglobulin M (IgM) or an IgA monoclonal gammopathy had a higher risk of progression than those with an IgG monoclonal gammopathy. The presence of a urine M-protein or the reduction of one or more uninvolved immunoglobulins was not a risk factor for progression.24 An early study that included 398 patients (270 whites and 128 blacks) showed that blacks had a two times (14.8%) higher incidence of MGUS than did whites (7.8%); this difference was statistically significant, and was noted across all age subgroups.25 In a community-based study from the Duke Established Populations, of 1732 patients over age 70, 106 subjects (6.1%) had MGUS. There was a twofold difference in prevalence between blacks (8.4%) and whites (3.8%), P < .001. This biological racial difference is associated with susceptibility to an early event in the carcinogenic process leading to MM.26 In a study from Zaragoza, Spain, the yearly incidence of monoclonal gammopathy remained stable up to 1985; from that time on, a 30-40% yearly increase was noticed, which was mainly related to MGUS and is a reflection of improved diagnosis and more vigorous application of testing to the elderly.27 The increased rate is also noted for patients diagnosed between 1976 and 1997 in Iceland. There was an increased incidence noted between 1976 and 1980 from 5.8 (men) and 4.9 (women) to 14.7 (men) and 12.5 (women) during 1992-1997. Incidence rates were very low under 50 years of age and increased with age from 11 and 17/100,000 at age 50-54, to 169 and 119/100,000 at age 80-84, for men and women, respectively.28

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