Monoclonal gammopathy of undetermined significance (MGUS) is found in some patients with chronic inflammatory demyelinating polyneuropathy (CIDP), but whether it defines a distinct disease subtype has remained unclear. Using data from the International CIDP Outcome Study (ICOS), this prospective cohort study assessed the prevalence of paraproteinemia in CIDP against age- and sex-matched neurological controls (patients with axonal polyneuropathy or motor neuron disease) and compared clinical features, diagnostic findings, and treatment responses between CIDP patients with and without MGUS. Anti-MAG–positive patients were excluded, and treatment response was defined retrospectively as at least a 1-point improvement on the modified Rankin scale.
IgG paraproteinemia was significantly more common in CIDP than in controls, whereas IgM and IgA prevalences did not differ.
Compared with patients without MGUS, those with IgG MGUS less often had an acute clinical presentation (6% vs. 33%), more often had sensory deficits at onset (94% vs. 67%), and more often showed prolonged distal CMAP duration on nerve conduction studies (64% vs. 31%).
Despite these clinical differences, first-line treatment response rates were highly comparable. Eighty percent of patients with IgG MGUS responded to treatment, compared to 67 percent of CIDP patients without MGUS.
The study concludes that although IgG MGUS is more prevalent in CIDP and weakly associated with certain disease features, it does not constitute a separate clinical subgroup with unique treatment implications. Because MGUS carries a risk of malignant transformation and can signal CIDP mimics, it still warrants careful evaluation and follow-up. First-line treatments remain equally effective for both patient groups.
Key Points:
- IgG paraproteinemia is more common in CIDP than in controls, while IgM and IgA prevalences do not differ.
- IgG MGUS is weakly associated with some clinical and diagnostic features : less frequent acute onset, more frequent sensory deficits at onset, prolonged distal CMAP duration.
- Treatment response is similar regardless of MGUS status : first-line response rates were comparable between groups, suggesting standard CIDP treatments are equally effective in patients with IgG MGUS.
- IgG MGUS is not a distinct clinical subtype with unique features or treatment needs, but still requires follow-up with careful monitoring because of the risk of malignant transformation and the need to exclude CIDP mimics.
References:
CIDP With and Without Monoclonal Gammopathy of Undetermined Significance (MGUS): Comparison of Clinical Phenotype, Diagnostic Features, and Treatment Response. R. van Veen et al., J Peripher Nerv Syst. 2026 Mar;31(1):e70116. doi: 10.1111/jns.70116. PMID: 41819123; PMCID: PMC12981947.
Publish on behalf of the Scientific Panel on Neuropathies.