MGUS associated with fewer diseases than previously reported

According to data from a population-based study, monoclonal gammopathy of undetermined significance was significantly associated with only 14 diseases, not 75 as previously believed. These results may prevent patients from undergoing unnecessary procedures and treatments, according to the researchers.

Using serum samples from 17,398 residents of Olmsted County, Minn., the researchers tested for monoclonal gammopathy of undetermined significance (MGUS). They identified 605 cases of MGUS and 16,793 negative controls. The Mayo Medical Index provided the researchers with information on all diagnoses between Jan. 1, 1975 and May 31, 2006, resulting in 422,663 person-years of observation. Using Poisson regression adjusted for age, sex and person-years of observation, the researchers analyzed diagnostic codes to identify and verify associations previously reported.

The researchers confirmed a significant association in 14 of the 75 previously reported disease associations. Five of the 14 diseases were known to evolve from MGUS — multiple myeloma, amyloidosis, lymphoproliferative disorders, macroglobulinemia and other plasma cell proliferative disorders, according to the researchers. Important associations included hip and vertebral fractures, osteoporosis and hypercalcemia; these disorders were significantly increased with MGUS, even without multiple myeloma.

Associations between MGUS and chronic inflammatory demyelinating neuropathy (RR=5.9; 95% CI, 1.2-28.4) and autonomic neuropathy were also confirmed. A lack of association between MGUS and the other 61 diseases lead researchers to conclude that “most of these previously reported associations are either coincidental or clinically insignificant.”

The researchers also identified previously unreported associations, including mycobacterium infection and superficial thrombophlebitis. These associations were identified from a systematic analysis of 16,062 diagnostic disease codes.

“Our study suggests that caution is needed,” the researchers wrote. “Some previously reported disease associations (eg, rheumatoid arthritis) that were not confirmed may still merit further study if there is continued biologic rationale for a true association to exist.”

Rajkumar SV. Mayo Clin Proc. 2009;84:685-693.