[Potassium channel dysfunction at the lesion site in multifocal motor neuropathy as revealed by threshold electrotonus].

Multifocal motor neuropathy presents as a treatable muscular atrophy and is characterized by persistent conduction block and fasciculations or myokymia. Although the pathological findings at the lesion site revealed perivascular demyelination with little evidence of remyelination, the mechanism of conduction block is still unknown. We explored the threshold electrotonus, which registers membrane potential changes through threshold variation, at the lesion site. The findings were consistent with focal potassium channel dysfunction, with some evidence of depolarization block. The disrupted blood-nerve barrier and lack of Schwann cell-mediated extracellular potassium regulation may predispose the membrane depolarization, thereby accounting for the conduction block and fasciculations. Sensory nerve fibers are known to have more inward rectifiers, which take up the extracellular potassium, than motor fibers, and this may explain the sparing of these fibers.