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

BACKGROUND: 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.

METHODS: 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.

RESULTS: 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).

CONCLUSION: 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.