The pathological basis of conduction block in human neuropathies.

Conduction block was detected in patients with neuropathy by measuring a decrease in the size of the compound muscle action potential of more than 20% on proximal versus distal stimulation of the peroneal, median or ulnar nerve in the absence of excess temporal dispersion of the potential. The teased fibre analyses of nerve biopsies from four patients with "definite" and six patients with "probable" conduction block and from seven patients with neuropathy but without conduction block were compared. All patients with conduction block had significant demyelination (X% demyelinated and remyelinated fibres = 50%) while those without conduction block did not (X = 5.0%). Demyelination is the pathological basis of conduction block in human neuropathies.