Ninety-eight workers, 65 exposed to organic solvents and 33 unexposed, were examined in order to assess possible neurotoxic signs and symptoms related to solvent exposure. The study group, who were selected according to the type of exposure in a given work process, had been exposed to various types of solvents. The groups were comparable in regard to age, the history of brain traumas and other neurological diseases, and alcohol consumption. The exposed workers had more symptoms of intellectual impairment, poorer performances in psychological tests, and more often signs of cerebral asthenopia. Symptoms and signs of peripheral neuropathy were not significantly increased. Solvent exposure and neurotoxic signs and symptoms were mildly correlated in the study group. Such dose-effect correlations have previously been proved only in a few epidemiological studies. This warrants reevaluation of the risk of developing toxic encephalopathy during prolonged occupational exposure to solvents.

On the basis of previous investigations from occupational medicine, neurology, and neuropyschology, a retrospective evaluation was made of 21 painters in whom chronic toxic encephalopathy following exposure to organic solvents had been diagnosed during a stay in the Neurology Department of Gentofte Hospital, Copenhagen, in the period 1976-1980. All the painters had given up their jobs for this reason. The assumption of a causal relationship between the exposure and the intellectual impairment was supported by a possible dose-effect relationship. The chronic toxic symptoms had considerable social consequences. Five years later, ten had not gotten other jobs. The lack of working ability was correlated to advancing age, increasing exposure, and increasing intellectual impairment. According to the results of the study, conditions at work places ought to be changed in such a way that harmful exposure can be prevented in the future.

The findings of acute and/or chronic central and peripheral neurotoxic effects of organic solvents in workers from a previous controlled cross-sectional study (65 exposed and 33 unexposed) were re-assessed to ascertain whether the neurotoxic symptoms and signs had become chronic. These follow-ups were performed 5.5 years later by occupational medical and clinical neurological examination (59 exposed and 30 unexposed) and again 10.6 years later by a mailed questionnaire (53 exposed and 30 unexposed). Both follow-ups revealed more acute neurotoxic symptoms in the exposed workers than in the unexposed workers, but fewer than previously, and indeed, the current exposure to solvents had been reduced. However, at both follow-ups, the exposed workers showed significantly more symptoms of chronic encephalopathy, in particular, memory and concentration impairment. These latter symptoms had also significantly worsened in the workers who were still being exposed, while they were presently unchanged in the previously exposed workers who had been free of exposure for 6.6 years at the latter follow-up. On the other hand, symptoms of chronic encephalopathy had not appeared in the unexposed group. Among workers, both still and previously exposed, there were also social consequences in the form of occupational disqualification. According to the findings, long-term occupational exposure to organic solvents in concentrations that are not unusual at workplaces may lead to development of chronic neurotoxic symptoms.