PRINCIPLES OF TOXICOLOGY - Biology East Borneo

7.6 EVALUATION OF INJURY TO THE NERVOUS SYSTEM 153• A study of the patient’s history, including diseases, chronic health problems, drug use, andexposure to other industrial or environmental chemicals.• An evaluation of the patient’s mental status, as determined by various intelligence, memory,or mood tests.• An evaluation of the patient’s sensory, motor, reflex, and cranial nerve function. These areassessed by simple, noninvasive tests, some of which are described below.• An inspection of the patient’s work environment, which includes monitoring for theneurotoxic chemicals that may be implicated on the basis of results from the patient’sevaluative tests.Many clinical symptoms can often be indicators of CNS disturbance. These may include dizziness,vertigo, headache, mood swings, fatigue, memory loss, and various other cognitive disorders. Effectson the peripheral nervous system, specifically the peripheral sensory and motor neurons, are manifestedby changes in breathing rate, heart rate, tendon reflex, perspiration, and gastrointestinal function.Standardized tests for cognition include IQ tests and performance with discriminatory tasks. Anexample is the Wechsler Adult Intelligence Scale (WAIS), in which the subject is presented with a listof words of increasing difficulty and is asked to provide a definition. Since the results obtained oftendepend strongly on the way in which the test is administered, and may be particularly vulnerable tohidden biases, evaluations of cognitive skills are not without controversy. Similar tests, which rely onthe subject’s answers to certain questions, may be used to measure mood and memory effects. Adifficulty with using such tests to evaluate possible neurotoxicant exposure in the workplace is that,in order to measure a change in cognitive skills, the individual’s preexposure level of skill must beavailable for comparison. This is rarely the case.Less subjective than cognitive tests are the standard physiological measurements, such as heart andbreathing rate for autonomic nervous system effects, and sensory effects such as impaired hearing orvision. Decreased reaction time in response to a stimulus may indicate peripheral nervous systemeffects as well, and electroencephalograph (EEG), or “brain wave,” measurements present a noninvasivemethod for monitoring the central nervous system. With some large, easily accessible neurons,as exist in the legs or arms, changes in the conduction velocity along the axon may be measured directly.Behavioral TestsThere is a vast array of available behavioral tests, which may be performed on workers to indicatepotential neurotoxicity. These include measurements of reaction time to a stimulus, changes in dexterityas measured while performing various tasks, perception, motor steadiness, and general coordination.Sometimes cognitive and mood factors will be involved in determining the outcome of these tests aswell. Several batteries of standard neurobehavioral tests have been developed, such as the World HealthOrganization Neurobehavioral Core Test Battery and the Finnish Test Battery, and are routinely usedin industry around the world.An example of the type of neurobehavioral tests that may be administered is the Luria test foracoustic-motor function. The subject listens to a sequence of high and low tones, then repeats thepattern by knocking on a table with a fist for high tones and a flat hand for low tones. This test measuresboth acoustic perception and motor skills. Visual perception and hand dexterity may be measured withthe Santa Ana dexterity test, in which the subject must rotate, within a given time, a pattern createdwith moveable colored pegs.Because behavior is determined by many factors, neurobehavioral tests are useful only as a first-stepscreening procedure for neurotoxicity. Taking preventative steps on behalf of workers requiresknowledge of the neurotoxicants present, as well as their mechanisms of action which may result inthe observed behavioral effects.