Multifocal Motor Neuropathy: Decrease in Conduction Blocks and Reinnervation with Long-term IVIg

Background: Multifocal motor neuropathy with conduction blocks (MMNCB) is an immune-mediated motor neuropathy. Previous long-term IV immunoglobulin (IVIg) treatment studies have documented improvement in muscle strength and functional disability but revealed a concomitant increase in acute axonal degeneration (AD) and conduction block (CB).

Objective: To determine the long-term effects of IVIg therapy on clinical and neurophysiologic outcome measures in MMNCB patients responsive to IVIg.

Methods: The authors reviewed medical records of 10 patients with MMNCB for outcomes in muscle strength (Medical Research Council score), functional disability (Modified Rankin Disability score), CB, and AD. All patients had received IVIg (2g/kg in 5 days for 3 consecutive months), followed by monthly maintenance therapy.

Results: Patients were followed for an average of 7.25 years (range, 3.5 to 12 years). There was significant and sustained improvement in muscle strength and functional disability while on IVIg therapy. Furthermore, the authors found significant improvement in CB, decrease in AD, and evidence of reinnervation by the end of the follow-up period.

Conclusion: Long-term IV immunoglobulin therapy improves muscle strength and functional disability, decreases the number of conduction blocks and the extent of axonal degeneration, and promotes reinnervation. These findings differ from previous reports of deterioration in neurophysiologic outcome measures. Comparison of the IV immunoglobulin regimen in those reports and this study shows that the authors' patients were treated with significantly higher IV immunoglobulin maintenance doses. These findings have implications for the long-term treatment of patients with multifocal motor neuropathy with conduction blocks.