Relative slowing of the median antidromic sensory nerve conduction velocity to the ring finger in screening for carpal tunnel syndrome.

PURPOSE: This study analyzed the accuracy of the relative slowing of the antidromic sensory conduction velocity of the median nerve in comparison with the ulnar nerve, from the wrist to the ring finger, in the diagnosis of carpal tunnel syndrome (CTS). METHODS: Eighty-two patients had been referred consecutively to our department to confirm or exclude CTS. The antidromic sensory conduction velocities of the median nerve and the ulnar nerve from the wrist to the ring finger were determined. The difference between the 2 values was calculated to express the relative slowing of the median nerve compared with the ulnar nerve. Carpal tunnel syndrome was diagnosed when the patient had clinical symptoms compatible with CTS confirmed by an established electrophysiologic investigation. The accuracy of a relative slowing of 5 m/s, 10 m/s, and 15 m/s of the median antidromic sensory conduction velocity to the ring finger was determined to diagnose CTS. RESULTS: At a cut-off value of 5 m/s the sensitivity was 95%, the specificity was 63%, and the efficiency was 79%. At a cut-off value of 10 m/s the sensitivity was 90%, the specificity was 85%, and the efficiency was 88%. At a cut-off value of 15 m/s the sensitivity decreased to 83%, the specificity increased to 93%, and the efficiency was 88%. CONCLUSIONS: A high accuracy is achieved in the diagnosis of CTS by determining the relative slowing of the median antidromic sensory nerve conduction velocity from the wrist to the ring finger.