WHAT IS THE BEST DIAGNOSTIC INDEX OF CONDUCTION BLOCK AND TEMPORAL DISPERSION

In order to find the best diagnostic index of conduction block and abn ormal temporal dispersion, the amplitude, duration, and area of the co mpound muscle action potentials (CMAP) were studied in 40 normal contr ols and 28 patients with acquired demyelinating neuropathies. In the n ormal subjects, there was a substantial difference among the various n erves in the degree of CMAP amplitude reduction and CMAP duration prol ongation with proximal stimulation, and thus different criteria should be used for conduction block or abnormal temporal dispersion for a gi ven nerve. In 28 patients with demyelinating neuropathy, 58 of 207 (28 %) tested nerve segments showed nerve conduction velocity (NCV) eviden ce of demyelination. To identify ''demyelination'' in these segments, conduction block was best detected by the total area method in 71% of cases, and abnormal temporal dispersion was best by the negative-peak duration method. This study showed that the best diagnostic index for conduction block is the total area method and for abnormal temporal di spersion, the negative-peak duration method. (C) 1994 John Wiley and S ons, Inc.