Chronic inflammatory demyelinating polyneuropathy. Conduction failure before and during immunoglobulin or plasma therapy.

An earlier study has shown that patients with chronic inflammatory demyelinating polyneuropathy may improve after the infusion of fresh frozen plasma or high dose intravenous immunoglobulin. We studied 8 such responding patients with neurophysiological techniques. Before treatment all patients had decreased compound muscle action potentials (CMAP) and slowing of conduction. During several courses of treatment a progressive increase of the CMAPs occurred and in 5 patients a correlation between the CMAPs of the abductor pollicis brevis muscle and grasp force could be demonstrated. In 2 patients, increase in strength was correlated with shortening of the distal motor latency; no significant relationships were found between strength and conduction velocity. Different patterns in the distribution of conduction failure were observed. In 2 patients, lesions were distributed along the length of the motor fibres, whereas the sensory system was spared. In another 2 patients the lesions, most likely demyelinating, were localized distally and included the sensory system. The 4 remaining patients were more difficult to classify, but individually showed greater resemblance to one or other of the two described patterns. Different patterns of conduction failure may reflect different pathogenetic mechanisms.