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IVIg for Lower Motor Neuron Syndromes

Summary and Comment |
November 26, 2013

IVIg for Lower Motor Neuron Syndromes

  1. Michael Benatar, MD, MS, PhD

Routine IVIg is not warranted in progressive lower motor neuron syndromes without conduction block.

  1. Michael Benatar, MD, MS, PhD

Multifocal motor neuropathy (MMN) is a rare, immune-mediated, pure lower motor neuron (LMN) disorder that typically manifests initially with distal upper-extremity weakness and atrophy and may be confused clinically with progressive muscular atrophy (PMA). The electrophysiologic hallmark of MMN is the presence of conduction block at sites not prone to compression. A high proportion of patients with MMN also have high-titer anti-GM1 immunoglobulin M (IgM) antibodies. Neurologists have long recognized that patients with purely LMN syndromes should undergo a careful evaluation for conduction block and anti-GM1 antibodies to diagnose MMN, an eminently treatable disorder, before settling on a diagnosis of PMA. Whether all patients with progressive LMN syndromes, even those without conduction block, should undergo an empiric trial of immune modulatory therapy with intravenous immunoglobulin (IVIg) remains controversial.

Now, investigators report their experience of having treated 31 consecutive patients with progressive, limb-onset, purely LMN syndromes in whom there was no electrodiagnostic evidence of conduction block. Only 3 of 31 patients (9.7%) demonstrated objective evidence of modest improvement after monthly IVIg treatment for 3 months, 2 of whom also had high-titer anti-GM1 antibodies. Characteristics of the IVIg-responsive group included distal upper-extremity weakness at onset, normal creatine kinase levels, and neurogenic changes on EMG that were confined to clinically weak muscles.

Comment

For patients in whom a diagnosis of a degenerative motor neuron disease is being contemplated, it is tempting to embark on an empiric trial of IVIg based on the outside chance that multifocal motor neuropathy might be the underlying diagnosis and the belief that there is nothing to lose. The available evidence does not support this clinical approach. Not only may IVIg be associated with serious (albeit rare) side effects (e.g., myocardial infarction, renal failure, and stroke), in the absence of conduction block or an elevated anti-GM1 IgM antibody titer, the likelihood of meaningful clinical improvement is incredibly low.

  • Disclosures for Michael Benatar, MD, MS, PhD at time of publication Royalties Parker-Waichman LLC Editorial boards Cochrane Collaboration; Muscle & Nerve

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