Proving Damages in Toxic Torts: Nervous System Dysfunction
By Raymond Singer, Ph.D.
October, 1999
Contents
Lawyers are often frustrated by a lack of evidence demonstrating that a plaintiff has been affected by toxic chemicals. Diseases like cancer may take many years to develop, and they are difficult to connect with a specific chemical exposure.
In contrast, nervous system dysfunction often occurs at the same time as or soon after exposure. Deterioration in mental and nervous functions can be measured using modern neurotoxicological approaches, which can document damages in toxic torts.
When lawyers begin to examine a toxic tort case, they often hope to find the chemical in the plaintiff's body, providing proof of causation. Such proof is rarely available, however. Usually toxic tort investigations take place long after an injury has occurred, allowing ample time for the chemical to leave the body. There are, however, other ways to prove damages, like evaluating the plaintiff's symptoms and functional disabilities.
"Neurotoxicology" is the science of evaluating nervous system dysfunction caused by chemicals. The human nervous system is particularly vulnerable to toxic-chemical insults. Pesticides, herbicides, solvents, and heavy metals are examples of the many chemicals that can permanently disrupt nervous system function.
Damage to the system can be found long after the chemicals have left the body. In fact, brain function may provide the best indicator of toxicity, because brain tissue does not regenerate and deficits in brain function are easy to measure.
Brain Function
Neuropsychological testing offers an effective way to evaluate functional deficits of the nervous system. Testing is based on measurements established as objective in basic and clinical science. The Wechsler Adult Intelligence Scale, for example, serves as a standard for most neurotoxicity evaluations. Validated on both normal and diseased individuals and groups, it provides rich scientific and clinical insights for evaluating nervous system dysfunction.
Certain mental functions (for example, the ability to learn and remember new material) are more sensitive to disruption than others. Neuropsychologists measure ability to remember in a number of ways. They test the number of mental units that a person can associate, remember, and report back. An example of normal ability is remembering a seven digit telephone number. People affected by toxic chemicals often cannot remember a string of seven numbers.
Some skills are less sensitive to damage from chemical toxicity. For example, individuals with chemical toxicity can usually remember conceptual material that they learned long ago and have called on over the years. They also remember common historical information, like the names of recent U.S. presidents, even though they may not remember what they ate for breakfast. Vocabulary skills are also less sensitive to chemical toxicity and are easily measured.
By comparing mental functions that are sensitive to disruption from chemical toxicity, neuropsychologists can evaluate the probability of damages from toxic chemicals. A certain amount of divergence found in normal individuals is exceeded in the brain-damaged. Therefore, neuropsychologists can judge damages in an individual case without having performed a pre-exposure evaluation.
Other estimates of pre-exposure mental function can be derived from academic test scores, armed services' records, or any evidence of achievement, like patent applications or occupational status. Such material can provide evidence of the plaintiff's normal or above-normal ability before exposure compared with the current level of functioning.
Neurotoxicity causes personality changes. Irritability is common, often leading to serious disability expressed by temper tantrums, unusual fighting and aggressiveness, marital discord, and trouble with the law.
Personality changes can be marked and dramatic. An easygoing person may become testy and violent. References, particularly from people familiar with the plaintiff before and after the exposure, can document these changes.
Symptoms like fatigue and sexual dysfunction also show disruption of autonomic nervous system function. Although discussing sexual function may be embarrassing to the plaintiff, it may help the neuropsychologist to reach a diagnosis.
Peripheral Nervous System Function
The peripheral nervous system includes nerves leading to and from the skin and muscles in the arms and legs and is susceptible to toxic chemicals. Symptoms of peripheral nervous system dysfunction from chemicals include numbness, tingling, pain, and weakness of the limbs. This occurs when the peripheral nerves degenerate. Nerves in the leg, which are far from their root at the spinal cord, are particularly affected.
The speed of nervous impulses can be measured by a nerve conduction velocity (NCV) test. The nerve is stimulated through the skin with a short electrical impulse that causes it to depolarize and discharge electrical energy. An electrical sensing device monitors the nerve at another spot along its length. The pattern of response is displayed on a CRT screen to determine the time elapsed from stimulation to response. The distance the impulse traveled in the limb is measured to calculate the velocity in meters per second.
The equipment for this test is portable and widely available. NCV assessment has been used for many years to evaluate peripheral nerve dysfunction from toxic chemicals. The test results are objective and are recorded on a paper printout, which can then be put to use as demonstrative evidence.
Like any scientific test, the accuracy of the test depends on proper administration and interpretation. Limb temperature, which affects NCV, must be monitored to adjust the resulting NCV value to a standard temperature. The person's age is also a factor.
Choosing which nerves to measure is also critical. Some are resistant to neurotoxicity, requiring many years of exposure before slowing becomes evident, and may not be appropriate. More susceptible nerves are better indicators of health problems. For example, the sural nerve, located in the calf of the leg, is widely used in neurotoxicity tests and should be studied whenever peripheral neurotoxicity is suspected.
About the Author: Raymond Singer, Ph.D. is a neurotoxicologist and psychologist practicing in Santa Fe, New Mexico and New York City. His work has been presented at scientific meetings around the world, and his findings have been published in professional journals. Dr. Singer has served as an expert witness in litigation involving pesticides, herbicides, heavy metals, mixed chemical waste, and other toxic substances.
Copyright © 1999 Raymond Singer, Ph.D.. All rights reserved. No portion of this article may be reproduced without the express written permission of the copyright holder, except as follows: You may link this article to your website, either directly or through an ExpertLaw Library index page, provided your link does not depict this article, its author, or expertlaw.com in a negative manner.