Orthodromic sensory conduction along the ring finger in normal subjects and in patients with a carpal tunnel syndrome.

The purpose of the present study was to examine the value of measuring sensory conduction along the median and ulnar nerves of the fourth finger in the diagnosis of a carpal tunnel syndrome (CTS). In 23 controls, sensory conductions along median and ulnar nerves were identical. In 28 of 38 patients with CTS, stimulation of the ring finger revealed a reduced conduction velocity along sensory median nerve fibres in contrast to normal conduction along ulnar sensory nerve fibres. In 5 patients, a sensory action potential was absent over the median nerve and in another 5 sensory conduction was normal along both nerves. We conclude that testing of sensory conduction along the ring finger is useful in about 74% of patients with CTS, while in the remaining 26% other fingers must be examined to establish the diagnosis.