[Surface area--a new parameter for CMAP reading].

Abstract

The purpose of this study is to determine a data range of the surface area of compound muscle action potential (CMAP) in normal abductor pollicis brevis and abductor digiti minimi. 256 median nerves and 317 ulnar nerves which were proved to be normal by NCV and EMG studies were included. Computer-aided measurement of distal latency, amplitude and nerve conduction velocity plus author-designed negative surface area reading was done. The surface areas of different age groups ranged from 28.6 to 35.3 ms*mV in abductor pollicis brevis and 30.0 to 31.5 ms*mV in abductor digiti minimi. There is no significant difference between different ages and between both sexes. The surface area showed statistically significant correlation with amplitude but no correlation with distal latency and nerve conduction velocity. It is concluded that as the concept of surface area is widely accepted and the measurement technique is more easily available, to set up a normal data base of surface area of the routinely examined muscle is very important and the surface area of CMAP should be included into the interpretation of routine nerve conduction studies.