Multifocal motor neuropathy: diagnosis and treatment

Multifocal motor neuropathy (MMN) and some lower motor neuron syndromes are immune-mediated and treatable. These motor syndromes produce weakness that is typically distal and asymmetric, involves the arms early in the course of disease, and progresses slowly. Electrophysiologic abnormalities often include evidence of demyelination, especially focal conduction block, selectively on motor axons. High titers of serum IgM binding to GM1 ganglioside, alone or in a membrane environment, occur in 80-90% of patients with MMN. Treatments for MMN that commonly produce increased strength include IV human immune globulin (HIG) and cyclophosphamide. After an initial treatment with 2 g/kg of HIG, up to 80% of patients with MMN show short-term improvement. Long-term HIG treatment is useful in 60% of MMN patients and has few side effects but is costly. Intravenous cyclophosphamide treatment is effective in 70% of MMN patients but has significant toxicity, and is reserved for patients who have severe disease and do not respond adequately to HIG.