Relative refractory period: a measure to detect early neuropathy in alcoholics.

The absolute (ARP) and relative refractory period (RRP) of the median sensory nerve was determined in 26 control subjects and 24 alcoholics, nine of whom had symptoms of peripheral neuropathy. Recovery of latency to normal in response to the second stimulus was used to define RRP. A true RRP was calculated by subtracting ARP from measured RRP. Mean ARP for all subjects ranged from 0.75 to 0.80 msec; normal = 0.8 +/- 0.2 msec. The true RRP of control subjects was 2.1 +/- 0.5 msec, and for all alcoholic subjects it was 3.1 +/- 0.5 msec. True RRP for the nine symptomatic alcoholic subjects was 3.6 +/- 0.5 msec and 2.9 +/- 0.4 msec for those who were asymptomatic. Symptomatic and asymptomatic alcoholics differed significantly from one another, as well as from control subjects (P less than 0.001). Routine nerve conduction studies were normal in asymptomatic subjects. Three out of nine symptomatic alcoholics had increases in distal median motor or sensory latency, and three had slight slowing of median nerve conduction velocity. True RRP is more sensitive than routine measures of nerve conduction in the detection of axonal disorders influencing nerve conduction.