Comparison of multiple frequency vibrometry testing and sensory nerve conduction measures in screening for carpal tunnel syndrome in an industrial setting.

The value of vibrometry in the evaluation of carpal tunnel syndrome is controversial. Several investigators have suggested that vibrometry screening with multiple frequencies would improve the correlation and increase the sensitivity when screening for carpal tunnel syndrome. One hundred sixty-nine industrial workers from two manufacturing plants in southern Michigan were screened for median nerve impairment using both vibrometry (seven frequencies, 8-500 Hz) and electrophysiologic testing in each hand. The vibratory threshold at each frequency, as well as composite measures-Jetzer index and negative sums, were compared with electrophysiologic measures of amplitude and latency. The individual frequencies and the Jetzer index correlated with median sensory latency, but the relationships were weak (r = 0.22 to 0.32). Only at the lower frequencies (8, 16, and 32 Hz) did the vibratory threshold correlate with sensory amplitude; correlation ranged from 0.187 to 0.303. Vibration threshold sensation is most closely related to axonal loss or conduction block, but the earliest finding in carpal tunnel syndrome is that of demyelination; thus we would not expect an abnormal vibratory threshold with mild carpal tunnel syndrome. These results support this interpretation and suggest that vibratory screening for early carpal tunnel syndrome is not effective.