Changes of median nerve conduction velocity in rayon manufacturing workers: A 6-year cohort study

OBJECTIVES: We conducted a 6-year cohort study to evaluate the relationship between carbon disulfide (CS(2)) exposure and reductions in the motor and sensory nerve conduction velocity (MCV and SCV) of the median nerve. METHODS: Study subjects at baseline included 432 exposed workers and 402 unexposed workers. Among the exposed workers, 145 workers terminated CS(2) exposure during the follow-up period (ex-exposed workers). MCV and SCV were measured at baseline and followed up. CS(2) personal exposure concentration was measured two times a year during a 6-year follow-up period and mean (range) CS(2) exposure concentrations (ppm) were 5.96 (0.8-16.0) and 3.93 (0.6-9.9) in the exposed and ex-exposed workers, respectively. RESULTS: Reductions in MCV during the follow-up period did not differ among the exposed, ex-exposed, and unexposed workers. Reduction in SCV (m/s) of the exposed workers (-4.47±3.94) was significantly larger than that of the unexposed (-3.38±3.97) and ex-exposed workers (-3.26±3.79). For SCV reduction, a partial multiple regression coefficient of (ex-exposed workers) / (unexposed workers) was significantly positive (+0.915, p < 0.01) after adjustment for confounding variables. CONCLUSIONS: This cohort study showed that 6-year CS(2) exposure around a mean level of 6 ppm did not affect MCV reduction but induced significant SCV reduction beyond the influence of aging. The effect of CS(2) on SCV around a mean exposure level of 4 ppm may be reversible, since it disappeared in the ex-exposed workers after CS(2) exposure cessation for a mean period of 4.1 years.