We compared the predictive values of three measurements of sensory conduction of the median nerve at the carpal tunnel (maximum latency difference [MLD], 8-cm latency [S8], and 14-cm latency [S14]) in 2334 hands of industrial workers, workers' compensation patients, and students. The MLD was determined by the centimetric technique. The MLD was the most sensitive and efficient measurement for predicting carpal tunnel syndrome (CTS). An MLD > or = 0.40 ms correctly identified 86.3% of 753 hands with CTS. The MLD correlated best with CTS and with the primary diagnostic category (CAT). MLD was the second factor selected in stepwise regression analysis for CAT (numbness was first and S8 was third). The MLD was the most important factor for predicting persistent or de novo CTS in a 5-year follow-up of 630 hands. Thus, the MLD was the most reliable nerve conduction study measurement for predicting current or future CTS in these subjects' hands.

We investigated the effects of three legal drugs (tobacco, caffeine, and alcohol) on the prevalence of carpal tunnel syndrome (CTS) confirmed by nerve conduction studies (definite CTS) in two groups of American industrial workers: 656 nonclaimant workers and 808 working patients referred for upper extremity symptoms. Comparing workers with definite CTS to workers without definite CTS revealed 26% greater current use of tobacco, 19% greater lifetime use of tobacco, 5% greater current use of caffeine, 14% lesser current use of alcohol, and 75% greater history of alcohol abuse in the workers with definite CTS. All these differences were statistically significant. Those who currently used alcohol but not tobacco or caffeine were at the lowest risk for slowing, symptoms, and definite CTS. Those who currently used caffeine alone or in combination with tobacco were at the highest risk. In female workers, current smoking, current caffeine use, and current coffee consumption independently predicted 5.0% of the explainable risk for definite CTS. In male workers, history of alcohol abuse and current beer consumption independently predicted 3.0% of the explainable risk for definite CTS. Prevalence of slowing, symptoms, and definite CTS in 12 specific job categories correlated directly with current tobacco use. We conclude that the use of legal drugs affects the prevalence of median nerve slowing, symptoms, and carpal tunnel syndrome, but the effects of the drugs independently explain only a small portion of the total risk. Nevertheless, legal drug use or abuse may serve as a marker for increased CTS risk.

We evaluated the natural history of median nerve sensory conduction, hand/wrist symptoms, and carpal tunnel syndrome (CTS) in an 11-year longitudinal study of 289 workers from four industries. Twenty hands which had carpal tunnel release surgery were excluded, leaving 558 hands for the primary study group. Overall, the trend was for mean sensory latencies and prevalence of slowing to increase, the prevalence of symptoms to decrease, and the prevalence of CTS to remain unchanged. Among individual hands, nerve conduction abnormalities tended to persist (82% 11-year persistence), while symptoms fluctuated widely (13% 11-year persistence). There was a strong, direct linear correlation between initial severity of slowing and subsequent development of CTS; however, most workers who developed de novo slowing did not develop symptoms or CTS. We conclude that changes in conduction status of the median nerve occur naturally with increasing age and do not necessarily lead to symptoms and CTS. Carpal tunnel syndrome (CTS) is the clinical expression of the most frequently diagnosed entrapment neuropathy of the upper extremity. 5,15,18,19 Confirmation of the diagnosis of CTS involves objective validation of median nerve abnormality within the carpal tunnel. 5,6,20 The most reliable method with which to obtain this objective confirmation is electrodiagnostic studies. 5,20 Longitudinal studies are required to determine the natural history of any chronic disease or pathologic process, including median neuropathy; cohort studies provide the most reliable evidence for trends in individuals. 4 With regard to median nerve slowing and CTS, we know of only two such longitudinal studies, including our previously reported 5-year follow-up of this same sample of industrial workers. 3,12 As part of an ongoing study of the etiology of median nerve slowing and CTS in industry, we evaluated a group of 283 industrial workers three times over a period of 11 years. This longitudinal study provides objective information on long-term trends in CTS in this population. It has excluded 20 hands which had carpal tunnel release surgery (CTR) (16 during 11-year interval, 4 prior to inception of study). This article presents our findings with regard to nerve conduction studies, self-reported hand/ wrist symptoms, and an objectively confirmed case definition of CTS. We hypothesized that median nerve sensory latencies, symptoms, and CTS would increase over time and that the development of symptoms and CTS would correlate with the progression of the median nerve slowing.

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