Impact of plasma exchange on indices of demyelination in chronic inflammatory demyelinating polyradiculoneuropathy

We studied the impact of plasma exchange (PE) on indices of primary demyeli nation in patients of the Canadian multicenter trial of PE in chronic infla mmatory demyelinating polyneuropathy (CIDP). Individual motor nerves (media n, ulnar, peroneal, tibial) were studied: distal motor latencies (DMLs), pr oximal and distal compound muscle action potential (M-wave) amplitudes, neg ative peak areas and durations, and motor conduction velocities (CVs). Prox imal M-wave amplitudes in individual motor territories, particularly in the ulnar nerve (from below elbow, above elbow, and axillary stimulating sites ) demonstrated significant improvement with PE, but not sham exchange. Prox imal ulnar M-wave areas also had significant improvement with PE. Trends to ward improvement of individual nerve motor CVs, M-wave durations, and DMLs did not achieve statistical significance. Proximal M-wave amplitudes, parti cularly in the ulnar motor territory, and proximal M-wave areas (providing a measure of conduction block) were the most sensitive indices of improveme nt conferred by PE in CIDP. In individual patients, these indices may help judge the efficacy of therapy. (C) 2000 John Wiley & Sons, Inc.