Slowing of sensory conduction of the median nerve and carpal tunnel syndrome in Japanese and American industrial workers

As part of a continuing study of the causes of carpal tunnel syndrome (CTS) in industry, we measured sensory conduction of the median nerve in 101 Japanese furniture factory workers. We used the maximum latency difference (MLD) with a critical value of ≥0.40 msec to indicate abnormal slowing of nerve conduction. The prevalence of slowing in the Japanese workers was 17.8%, while the prevalence of probable CTS (based on symptoms only) was 2.5%, and the prevalence of definite CTS (probable CTS confirmed by slowing) was 2.0%. The most important factor predicting the MLD was the body mass index. The MLD was the most important factor predicting probable CTS. The prevalence of slowing in the Japanese workers was not significantly different from the prevalence of slowing in 316 American workers from four industries (22.0%), but the prevalences of probable CTS and definite CTS were much lower in the Japanese. The meaning of these findings is discussed.