PRINCIPLES OF TOXICOLOGY

• A study of the patient’s history, including diseases, chronic health problems, drug use, and
exposure 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 are
assessed by simple, noninvasive tests, some of which are described below.
• An inspection of the patient’s work environment, which includes monitoring for the
neurotoxic chemicals that may be implicated on the basis of results from the patient’s
evaluative 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. Effects
on the peripheral nervous system, specifically the peripheral sensory and motor neurons, are manifested
by changes in breathing rate, heart rate, tendon reflex, perspiration, and gastrointestinal function.
Standardized tests for cognition include IQ tests and performance with discriminatory tasks. An
example is the Wechsler Adult Intelligence Scale (WAIS), in which the subject is presented with a list
of words of increasing difficulty and is asked to provide a definition. Since the results obtained often
depend strongly on the way in which the test is administered, and may be particularly vulnerable to
hidden biases, evaluations of cognitive skills are not without controversy. Similar tests, which rely on
the subject’s answers to certain questions, may be used to measure mood and memory effects. A
difficulty 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 be
available for comparison. This is rarely the case.
Less subjective than cognitive tests are the standard physiological measurements, such as heart and
breathing rate for autonomic nervous system effects, and sensory effects such as impaired hearing or
vision. Decreased reaction time in response to a stimulus may indicate peripheral nervous system
effects as well, and electroencephalograph (EEG), or “brain wave,” measurements present a noninvasive
method 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 Tests
7.6 EVALUATION OF INJURY TO THE NERVOUS SYSTEM 153
There is a vast array of available behavioral tests, which may be performed on workers to indicate
potential neurotoxicity. These include measurements of reaction time to a stimulus, changes in dexterity
as 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 as
well. Several batteries of standard neurobehavioral tests have been developed, such as the World Health
Organization Neurobehavioral Core Test Battery and the Finnish Test Battery, and are routinely used
in industry around the world.
An example of the type of neurobehavioral tests that may be administered is the Luria test for
acoustic-motor function. The subject listens to a sequence of high and low tones, then repeats the
pattern by knocking on a table with a fist for high tones and a flat hand for low tones. This test measures
both acoustic perception and motor skills. Visual perception and hand dexterity may be measured with
the Santa Ana dexterity test, in which the subject must rotate, within a given time, a pattern created
with moveable colored pegs.
Because behavior is determined by many factors, neurobehavioral tests are useful only as a first-step
screening procedure for neurotoxicity. Taking preventative steps on behalf of workers requires
knowledge of the neurotoxicants present, as well as their mechanisms of action which may result in
the observed behavioral effects.