Epidemiology of occupational neurobehavioural hazards. Methodological experiences from organic solvent research

Neurobehavioral hazards have been identified since long in occupational health, e.g. lead, mercury, certain solvents, and many others agents. There are reviews and books on "Occupational neurology" or "Prevention of neurotoxic illness in working populations". Many methods have been applied for studies of the central and peripheral nervous systems in humans: registered diagnoses, questionnaire ratings, clinical evaluation, psychometric tests, neurophysiological and neuroradiological methods, cerebrospinal fluid components etc. Some neurological disorders are well defined, while neuropsychiatric syndromes often are less precisely diagnosed. Decreased subclinical test results in exposed groups might predict an increased risk for later, more serious disorders but the longitudinal information on clinical importance is often lacking. Some historical lessons from the epidemiology of occupational neurology will be repeated and a few reflections on the suitability of different diagnostic entities for epidemiological research shall be made. Since the beginning of the 1970s' a number of studies from the Scandinavian countries have demonstrated long-term neurobehavioral effects from working conditions with relatively moderate exposure to organic solvents. Similar findings have been verified in studies from some countries outside Scandinavia while other studies have been inconclusive. Those results have caused considerable controversy and have been discussed at international conferences and in scientific journals. Very different outcomes have been investigated in those solvent studies, however, and most studies have had a cross-sectional design with inherent problems. The exposure has been assessed in different ways, e.g. by years of occupation, hygienic measurements of the present working conditions, biological monitoring, retrospective assessments on qualitative or semi-quantitative scales. Sometimes single solvent exposures have been studied but most of the studies concern mixtures of solvents from aromatic and aliphatic hydrocarbons. As the designs have varied the exposure assessment has been crude and many different outcomes have been studied, it is hardly surprising that the results and the interpretations have differed. The first results from a comprehensive investigation on 135 solvent exposed painters and 71 carpenters as referents, selected from active members of the respective trade union 1965-70 and investigated in the late 80s, will be presented. Clinical, including psychiatric, diagnostic work up and neuropsychological as well as neurophysiological tests have been performed. Psychological test results from military conscripts at age 19 were available for all. The individual exposure history has been carefully assessed.(ABSTRACT TRUNCATED AT 400 WORDS)