CIDP With and Without Monoclonal Gammopathy of Undetermined Significance ( MGUS ): Comparison of Clinical Phenotype, Diagnostic Features, and Treatment Response

Background and Aims Monoclonal gammopathy of undetermined significance (MGUS) occurs in some patients with chronic inflammatory demyelinating polyneuropathy (CIDP), but its impact on clinical phenotype and treatment response remains unclear. We assessed the prevalence of paraproteinemia in CIDP and compared disease features between CIDP patients with and without MGUS. Methods We used data from the International CIDP Outcome Study (ICOS), a prospective cohort study. We compared the prevalence and causes of paraproteinemia in CIDP to matched disease controls (axonal polyneuropathy or motor neuron disease) and compared disease features and treatment responses between CIDP patients with and without MGUS. Treatment response, defined as a ≥ 1‐point improvement on the modified Rankin scale, was retrospectively assessed. Results IgG paraproteinemia was more common in CIDP than in controls (9%, 17/193 vs. 3%, 6/192; p = 0.03). IgM and IgA paraprotein prevalences did not differ. One CIDP patient had Waldenström macroglobulinemia; others had MGUS. Patients with IgG MGUS less often had an acute clinical presentation (6% vs. 33%; p = 0.02), more often had sensory deficits (94% vs. 67%; p = 0.02), and prolonged distal CMAP duration (64% vs. 31%; p = 0.02), compared to patients without MGUS. First‐line treatment response rates were comparable (80% [IgG MGUS] vs. 67% [no MGUS]; p = 0.39). Interpretation IgG MGUS is more prevalent in CIDP than in controls. Presence of IgG MGUS is weakly associated with some CIDP disease features, but not treatment response. These findings indicate that, although IgG MGUS is associated with CIDP, the presence of IgG MGUS does not constitute a distinct subgroup with unique clinical features or treatment implications.