Sensory latencies to the ring finger: normal values and relation to carpal tunnel syndrome.

Sensory innervation to the ring finger (digit IV) is generally shared by the digital branches of the median and ulnar nerves. In 74 hand studies on 37 normal adults, all had a recordable response in digit IV upon stimulation of the median and ulnar nerves antidromically 14cm proximally to the recording electrodes. Comparing the median sensory latency to digit IV with the ulnar sensory latency to the same digit, the difference was 0.3msec or less in 93% of the hands. In 18 cases of carpal tunnel syndrome, the difference ranged from 1 to 2.1msec. This procedure may be of value as an easily performed and rapid technique to screen vulnerable nerve syndromes for possible entrapment and to provide baseline data for asymptomatic hands in individuals with carpal tunnel syndrome.