[Multifocal-motor neuropathy and motor neuropathy with multifocal conduction block (Lewis-Sumner syndrome)]

Multifocal motor neuropathy, which mimics lower motor neuron disease, is a rare and curious demyelinating neuropathy characterised by slowly progressive, asymmetric limb weakness within the distribution of individual peripheral nerves, wasting, cramps, fasciculations and rare sensory involvement, but without upper motor neuron signs. The cardinal feature and primary pathophysiological basis for the weakness is the multifocal motor conduction block which remains stable for years at the same site and is confined to motor axons. It is defined as > 50% reduction in both the CMAP and the negative peak area on proximal stimulation, as compared with the distal stimulus response without any change in the negative peak duration. Nerves at the site of the conduction block show demyelination, endoneural edema, rudimentary onion bulbs and lymphocytic inflammation. Sensory nerves may show mild demyelination, axon loss and lymphocytic inflammation. The majority of patients shows elevated titers of anti-glycolipid antibodies, which may block the Na+ channels, produce demyelination or interfere with remyelination. However, their role in the pathogenesis of multifocal motor neuropathy remains uncertain. Multifocal motor neuropathy is regarded as the predominantly motor variant of chronic inflammatory demyelinating polyneuropathy and can be treated best with immunoglobulins and cyclophosphamide.