Clinical and pathological heterogeneity in a series of 31 patients with IgM-related neuropathy

BACKGROUND: IgM-related neuropathy generally presents as a late-onset demyelinating polyneuropathy with predominant sensory loss and ataxia. Sporadic cases with atypical presentation have been described. PATIENTS AND METHODS: We report clinical and pathological findings from 31 patients with IgM-related neuropathy followed in our Institute of Neurology over a 20-year period. RESULTS: Typical presentation with predominant sensory ataxic neuropathy was observed in 18/31 patients. In the remaining 13/31 (42%), we observed an atypical phenotype, characterized by multiple mononeuropathy or polyneuropathy with predominant motor impairment; one patient had polyneuropathy with predominant small-fibre involvement. Uncommon pathological findings consisting in inflammatory infiltrates, focal axonal loss or light chain deposition were observed in 8 patients, all with atypical clinical phenotype. Almost all patients with atypical phenotype improved with immunosuppressive therapy. CONCLUSIONS: A significant proportion of patients with IgM-related neuropathy presents with atypical clinical features. In these patients, sural nerve biopsy helps clarify heterogeneous disease mechanisms and identify patients who might benefit from immunosuppressive therapy.