Applications of neurophysiological methods in occupational medicine. A review

Abstract

Certain physical and chemical agents causing occupational diseases with neurological symptoms are discussed with special reference to neurophysiological findings. The most common lesion of the peripheral nervous system caused by an occupational agent is polyneuropathy. In many instances the neuropathy is more striking in the distal portions of the nerves, as in the case of lead, acrylamide, CS2 and vibration induced neuropathy. Only alkyl mercury neuropathy distinctly involves the whole length of the sensory axon at an early stage. In most cases neuropathy at current exposure levels is mild or subclinical; this is displayed well by the fact that more sensitive and more refined techniques are being developed in order to detect the effects of neurotoxic substances. Myopathy caused by industrial poisonings has not been reported, but disturbances of myoneural junction are found in insecticide exposure and in CS2 poisoning. Encephalopathy is no doubt a potential danger, especially in exposure to various solvents (CS2, styrene or other hydrocarbons) and perhaps in chronic CO exposure. A combination of EEG abnormalities and signs of peripheral neuropathy is suggestive of effects of a neurotoxic substance. It is concluded that neurophysiological methods in occupational medicine are useful in the following aspects. 1) In the study of neurotoxicity of known or new chemicals or the neurological involvement caused by physical factors. Strictly controlled epidemiologic studies of humans or well planned animal experiments are the most informative. However the knowledge derived from animal experiments cannot be directly applied to man, since certain species specific variations in effects are common. 2) In the setting of safety norms. Nervous involvement must always be considered unacceptable, and, when such signs are present, exposure levels should be lowered. 3) In the early diagnosis in cases of suspected occupational diseases. Furthermore, neurophysiological examination may aid in deciding whether or not the patient qualifies for workmen's compensation. 4) In making the decision whether or not a worker may remain exposed. It is important to lower the exposure level, or to stop harmful exposure periodically or totally, early enough to prevent permanent lesions. At an early stage neurotoxic effects are often reversible. 5) In detecting especially vulnerable workers. Persons with nervous system diseases should be excluded from work with exposure to neurotoxic chemicals. (74 references are cited).