[Evaluation of digital vibration threshold for asymptomatic ulnar neuropathy in patients with carpal tunnel syndrome]

Quantitative assessment of vibration threshold at 125 Hz of index and little finger tips together with measurements of median and ulnar sensory nerve conduction velocity (SNCV) was performed for 25 limbs of 15 patients with carpal tunnel syndrome (CTS), 25 limbs of 13 disease controls with neurological symptoms similar to CTS and the nearly same number of limbs of normal controls. There was no significant difference in ulnar SNCV among 3 groups. However, ulnar SNCV at wrist was significantly reduced in patients with CTS as compared with normal value. In 17 limbs with CTS, vibration threshold of index finger tips was significantly increased, and 8 of those limbs were found to have concomitant increase of vibration threshold of little finger tips. Most of patients with increase of vibration threshold of both index and little finger tips were those who used to expose to repetitive mechanical stimuli at the wrist in their occupation. It was concluded that digital vibration threshold is simple to measure yet sensitive enough to detect asymptomatic ulnar neuropathy in CTS.