Transcarpal median sensory conduction: detection of latent abnormalities in mild carpal tunnel syndrome.

The major slowing of nerve conduction in the carpal tunnel syndrome is located in the palm to wrist segment. The aim of this study is to develop a reliable, sensitive and accessible approach to measure transcarpal median sensory nerve conduction. For this purpose, a fast recovery amplifier with a stimulus artifact suppressor was designed by the author. On stimulation of digits II or III, evoked orthodromic sensory nerve action potentials were simultaneously recorded at the palm and at the wrist. Distances were determined with a ruler. Median sensory nerve conduction velocity was estimated from digit to palm and from palm to wrist in 80 healthy hands and 253 hands with a presumptive diagnosis of carpal tunnel syndrome. According to conventional criteria, 131 of the 253 hands from those suspected of carpal tunnel syndrome were thought to have median nerve compression. When transcarpal median sensory conduction velocity was taken into account, the diagnostic yield increased by 18.1%. The described technique provides a simple, sensitive and reliable method of diagnosing mild or early carpal tunnel syndrome.