Comparison of the antidromic sensory nerve action potentials obtained from all fingers on the same hand

Supramaximal compound sensory nerve action potentials (CSNAPs) were recorded antidromically from five fingers of the same hand to electrical stimulation of the median, ulnar, and radial nerves in 17 normal subjects. The mean amplitudes of the median CSNAPs from the thumb, index, and middle fingers were similar in values. There was minimal radial sensory contribution to the thumb, with the mean radial CSNAP amplitude about one-fourth the size of the median CSNAPs. The mean median and ulnar CSNAP amplitudes from the ring finger were approximately half, and the mean ulnar CSNAP amplitude from the little finger was approximately 85%, of the median CSNAP amplitudes from the other fingers. The median, ulnar, and radial sensory nerve conduction velocities were close in values. There appears to be less variability in the population normative data when the size of the CSNAPs is expressed in terms of amplitude ratio rather than in absolute amplitude value.