Multifocal motor neuropathy (MMN) is a chronic immune-mediated peripheral myelinopathy. The major clinical features include slowly progressive, painless, and asymmetric weakness, usually of distal limb muscle. Early in the course of the disease, weakness is not necessarily associated with muscle trophy, owing to the initial primary involvement of peripheral myelin. Chronic progressive weakness is often associated with some degree of concurrent axonal loss and subsequent muscle atrophy. Sensory symptoms are usually mild or absent, and involvement of cranial and respiratory muscles in rare. The findings of multifocal motor conduction block, abnormal temporal dispersion, and focal conduction slowing at segments not at risk for common entrapment or compression injury, associated with normal sensory conduction studies along the same segments, are the hallmark electrophysiologic features of MMN. The slow progression and absence of upper motor neuron signs are the major clinical points that separate MMN from amyotrophic lateral sclerosis. The role of GMI antibodies, found in high titers in 22~84% of MMN patients, remains uncertain. The contention that MMN is an autoimmune disorders is largely based on the often dramatic improvement in symptoms following the administration of intravenous of immunoglobulin or cyclophosphamide.

Intravenous immunoglobulin (IVIg) is the treatment of choice for many autoimmune neuropathic disorders such as Guillain-Barre syndrome (GBS), chronic inflammatory Demyelinating neuropathy (CIDP), and multifocal motor neuropathy (MMN). IVIg is preferred because the adverse reactions are milder and fewer than the other immune-modulating methods such as steroid, other immunosuppressant such as azathioprine, and plasmapheresis. IVIg also has beenused in other autoimmune neuromuscular disorders (inflammatory myopathy, myasthenia gravis, and Lambert-Eaton myasthenic syndrome) and has been known as safe and efficient agent in these disorders. Since IVIg would get more indications and be used more commonly, clinicians need to know the detailed mechanism of action, side effects, and practical points of IVIg.