[On the mechanisms and diagnosis of conduction disturbances due to demyelination with special reference to multifocal demyelinating neuropathy (Lewis-Sumner)]

Abstract

Multifocal demyelinating neuropathy with persistent conduction block can mimic motor neuron disease, but is potentially reversible. Its diagnosis rests upon electrophysiological demonstration of focal conduction block at multiple sites. Conduction block is the most important mechanism causing clinical symptoms in peripheral nerve demyelination. On the other hand, conduction slowing is not always associated with clinical symptoms. In 2 out of 9 patients with multifocal demyelinating motor neuropathy, MRI showed focal swelling of the nerve at the site of conduction block. Both of them had elevated titers of anti-GM1 antibodies. In one, we biopsied a portion of the medial pectoral nerve, which was adjacent to the focal swelling, at surgical exploration. Pathological findings included very thin myelin associated with large diameter fibers and small onion bulb formation, suggesting that remyelinative process is abortive in this disease leading to persistent conduction block. Anti-GM1 antibodies bound to the denuded axoplasmic membrane may interfere with the process by masking the cell surface markers. The reason why the sensory fibers are spared is unclear, but it may be possible that GM1 in sensory axons have less affinity to the antibody than that in motor fibers.