Multifocal motor neuropathy: Clinical and electrophysiological findings

Multifocal motor neuropathy (MMN) is a treatable, probably immune-mediated neuropathy. Typical clinical symptoms are asymmetrical pure motor deficits in a peripheral nerve distribution, predominantly affecting distal parts of upper limbs. The characteristic electrophysiological findings of MMN are multifocal and often persistent conduction blocks that can be differentiated from untreatable motor neuron disease. Since demyelination in MMN is not as widespread as in chronic inflammatory demyelinating polyneuropathy (CIDP), nerve conduction velocities are often normal. To improve the diagnosis of conduction blocks, electrophysiological studies should include proximal nerve segments using special stimulation techniques. Antibody titres against GM(1) gangliosides may be elevated in MMN, but are not sufficient for diagnostic values. High dose intravenous immunoglobulins (IVIG) and cyclophosphamide are the only effective therapies in MMN, IVIG being the treatment of choice because of its less serious side effects. Corticosteroids and plasma exchange therapy may aggravate neurological deficits. Rapid improvement after IVIG application may be caused by neutralisation of functional blocking antibodies. IVIG is also effective in the long-term course. In some patients, however, disease progression may be observed despite of regular IVIG treatment. As long-lasting IVIG treatment is expensive, combination with cyclophosphamide may be performed to reduce the IVIG dosage. Application of further immunomodulatory drugs in MMN should be investigated in the future.