Patterns of motor nerve demyelination and their prognostic significance in multifocal motor neuropathy

TL;DR

This study identifies patterns of nerve damage in a rare nerve disorder that predict treatment response and disease severity.

Contribution

The study shows that temporal dispersion in nerves at onset is a novel marker for poor prognosis in multifocal motor neuropathy.

Findings

Patients with more nerves affected at onset had worse IVIg treatment response.

Temporal dispersion in multiple nerves marks a more severe disease course.

Combining temporal dispersion with conduction block improves prognosis prediction.

Abstract

Multifocal motor neuropathy (MMN) is a rare immune-mediated neuropathy characterized by motor nerve involvement and, typically, a good response to intravenous immunoglobulin (IVIg). However, a subgroup of patients shows poor or absent treatment response and a more rapid disease course. We aim to characterize clinical, laboratory, and electrophysiological features associated with IVIg response in MMN over a follow-up period of up to 20 years.

Thirteen patients fulfilling diagnostic criteria for definite MMN were retrospectively analyzed. Detailed clinical data, comorbidities, IVIg treatment regimens, and serial nerve conduction studies (NCS) were evaluated. Particular attention was given to the extent and distribution of conduction block (CB) and temporal dispersion (TD). IVIg response was defined as ≥ 1-point improvement in MRC strength in at least two muscle groups within 4 weeks after infusion or equivalent functional improvement documented in medical records.

Four of 13 patients (31%) showed poor or absent IVIg response. These patients exhibited a higher number of clinically and electrophysiologically affected motor nerves at disease onset (median 6 vs. 3, p = 0.014) and more nerves with TD (median 2.5 vs. 1, p = 0.025), compared to IVIg responders. CB alone did not reliably distinguish responders from non-responders (median 1 vs. 1, p = 0.74). Anti-GM1 IgM antibodies were detected in 44% of the patients tested, of whom 75% were non-responders. Comorbidities (e.g., diabetes II, malignancy, autoimmune disease) were more frequent among non-responders.

A pattern of early nerve involvement with prominent TD appears to be associated with a more aggressive disease course and poorer IVIg response. Diagnostic evaluation in MMN should not focus solely on focal CB but also systematically assess the number of nerves with TD. Prospective studies with standardized protocols are needed to validate these findings.

●Limited nerve involvement predicts favorable IVIg response.●TD across multiple nerves at onset marks more severe disease.●Adding TD assessment to CB improves prognostic stratification in MMN.

Limited nerve involvement predicts favorable IVIg response.

TD across multiple nerves at onset marks more severe disease.

Adding TD assessment to CB improves prognostic stratification in MMN.

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