Prognosis of polyneuropathy due to IgM monoclonal gammopathy: a prospective cohort study

The disease course of polyneuropathy associated with immunoglobulin M monoclonal gammopathy (IgM MGUSP) can be highly variable. In order to identify factors that influence long-term disease outcome, a prospective cohort study was performed of 140 patients with IgM MGUSP over a period of 23 years.

All patients with IgM MGUSP who were diagnosed in our tertiary referral center for polyneuropathy were eligible. All patients underwent nerve conduction studies and were tested for anti-MAG antibodies. The modified Rankin Scale, graded muscle strength, quantified sensory function, and laboratory testing were performed at 0, 1, 2, and 5 years and at last visit. The primary outcome measure was the risk of developing a modified Rankin Scale score of > or = 3 points.

A total of 140 patients with IgM MGUSP fulfilled inclusion criteria (101 [72%] demyelinating, 39 [28%] axonal, 63 [44%] MAG positive). The median age at onset was 59 years (interquartile range 52-67), median disease duration at baseline was 3.2 years (interquartile range 1.9-6). Anti-MAG antibodies were associated with a lower risk of Rankin Scale score > or = 3. Demyelination and a higher age at onset were associated with a higher risk for Rankin Scale score > or = 3. Based on these 3 factors, a Web-based prognostic model was developed that directly allows clinicians to estimate the probability of developing disability (http://www.umcutrecht.nl/subsite/Prognosis-MGUS-Neuropathy).

Higher age at onset and demyelination increase the risk, whereas anti-MAG antibodies decrease the risk, of developing Rankin Scale score > or = 3 in polyneuropathy associated with immunoglobulin M monoclonal gammopathy (IgM MGUSP). Our Web-based prognostic model allows determination of prognosis in IgM MGUSP.