Motor and multifocal motor neuropathies

Introduction
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By Rebecca E Traub MD and Thomas H Brannagan III MD

Motor neuropathies and multifocal motor neuropathy with conduction block are treatable causes of neuropathy that present with the clinical syndrome of asymmetric motor weakness with atrophy, which may mimic amyotrophic lateral sclerosis. The diagnosis of the disorder relies on the typical clinical presentation as well as electrodiagnostic findings of conduction block at noncompression sites and often on anti-GM1 IgM antibodies on serum testing. The mainstay of therapy includes intravenous immunoglobulin, but often other immunomodulating therapy is required for long-term management. In this clinical summary, Drs. Traub and Brannagan of Columbia University have reviewed the most recent literature covering pathophysiology, diagnostic criteria, and treatment for motor neuropathy.

Key points

  • Multifocal motor neuropathy is a treatable cause of neuropathy that may mimic amyotrophic lateral sclerosis.
  • The diagnosis of multifocal motor neuropathy relies on the typical clinical presentation, electrophysiology demonstrating conduction block at noncompression sites, and the presence of anti-GM1 IgM antibodies.
  • The primary diseases to consider in the differential diagnosis of multifocal motor neuropathy include amyotrophic lateral sclerosis, chronic inflammatory demyelinating polyneuropathy, and Lewis Sumner syndrome.
  • Motor neuropathies and multifocal motor neuropathy often respond to treatment with intravenous immunoglobulin, but in some patients, long-term management requires the use of other immunosuppressant medications.