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IVIg Modestly Improves Electrophysiology in Multifocal Motor Neuropathy

That there is some benefit seems clear, but the modest improvement underscores the need for better treatments.

Multifocal motor neuropathy (MMN) is characterized by weakness, atrophy, fasciculation, and cramps in the distribution of a few peripheral nerves, with motor conduction block (MCB) and normal sensory conduction. The primary pathology is inflammatory demyelination, but associated axonal degeneration is invariably also present. IVIg treatment produces clinical improvement that is rarely sustained. Improvement may be due to resolution of MCB, but documentation is sparse; some patients improve without a change in MCB, and new MCBs may appear during treatment. Also, axonal degeneration continues during treatment.

Vucic and colleagues examined whether clinical improvement occurred, was sustained, and was paralleled by improvements in MCB and muscle innervation during 3.5 to 12 years of treatment with IVIg (mean dose, 163 g/kg once every 4 weeks) in 10 patients with MMN. They evaluated patients clinically using summed strength scores and functional motor assessment, and electrophysiologically using standard measures of MCB. They performed needle EMG of affected muscles to assess denervation and reinnervation.

Strength and motor function improved after the first treatment course and then remained stable. Two patients' conditions deteriorated when treatment was withdrawn or reduced. MCB resolved in 17 of 29 nerve segments by the last follow-up. Four newly affected segments appeared during treatment; whether these patients clinically deteriorated is not stated. On average, clinical improvement was accompanied by a reversal of MCB, reduced axonal degeneration, and increased axonal regeneration. Indicators of reinnervation increased, whereas abnormal spontaneous activity decreased. The researchers saw evidence of continuing denervation-reinnervation (i.e., denervation followed by reinnervation) in all muscles.

The authors conclude that improved strength occurred, was sustained during long-term IVIg treatment, and was accompanied by reversed or reduced MCB and reinnervation of affected muscles. Treatment was incompletely effective, as new segments of MCB and ongoing muscle denervation occurred during treatment. They note that these results differ slightly from those of an earlier study (Brain 2002; 125:1875) in which treatment was less effective, perhaps because of a lower IVIg dose (mean, 0.54 g/kg/4 weeks).

Comment: It is intuitive that improved strength should be accompanied by a reversal of MCB and reinnervation of affected muscles. That this association has not always been found probably reflects a failure to study the most proximal nerve segments that were included in this study. These results suggest that the IVIg dose is important; the dose in this study was larger than that in previous studies. It is disappointing that this extremely expensive and inconvenient treatment was only partially effective, as new MCBs and new denervation developed during treatment. Multifocal motor neuropathy calls desperately for a more effective treatment.

— Gareth J. Parry, MD

Dr. Parry is Professor of Neurology, Department of Neurology, University of Minnesota, Minneapolis.

Published in Journal Watch Neurology February 11, 2005

Citation(s):

Vucic S et al. Multifocal motor neuropathy: Decrease in conduction blocks and reinnervation with long-term IVIg. Neurology 2004 Oct 12; 63:1264-9.

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