Clinical validation of antidromic stimulation of the ring finger in early electrodiagnosis of mild carpal tunnel syndrome.

Median and ulnar sensory distal latencies were measured antidromically on the fourth finger in 158 patients (224 hands) with suspected carpal tunnel syndrome (CTS), in 60 normal subjects (100 hands), and in 30 patients (30 hands) who suffered from paresthesiae due to a cervical spondylotic radiculopathy (CSR). The difference between these 2 latencies was less than 0.4 msec in all normals and patients with CSR, while in all of the patients with CTS it was more than 0.5 msec. Median sensory nerve conduction was significantly slower for the fourth than for the second finger in the CTS group, but not in controls. The difference between median and ulnar sensory distal latencies on the fourth finger proved to be the most sensitive of the tested parameters and was the only abnormal one in 20% of the clinically affected hands. The ring finger technique is a quick and easy procedure, which should be recommended in the early diagnosis of mild CTS.