[Sensory action potentials of ring finger in the diagnosis of carpal tunnel syndrome].

Amplitudes and latencies of sensory action potentials (SAPs) recorded over the index, middle, little and ring fingers by antidromic stimulation of the median or ulnar nerve at wrist were measured in 65 normal adults and 78 patients with clinically and electrophysiologically verified carpal tunnel syndrome. In the normal adults, there was no significant difference among the SAP latencies of the index, middle, ring and little fingers. Among these 65 normal adults, the difference between median and ulnar SAPs of ring finger was less than 0.4 msec in 64 subjects, but 0.7 msec in one. In the patient group, the median distal sensory latency of the ring finger was significantly longer than that of the ulnar nerve which was recorded over the ring and little fingers. Six cases (7.7%) of 78 patients diagnosed as CTS by conventional electrophysiological studies was false negative by using the ring finger sensory action potential study. It is suggested that the SAP study of the ring finger by stimulation of the median and ulnar nerves at the wrist can not replace the conventional electrodiagnostic methods for the diagnosis of carpal tunnel syndrome.