Wood-Preserving Chemicals, Multiple Sclerosis, And Neuropsychological Function


Multiple sclerosis (MS) is diagnosed when a patient has symptoms, relapsing or remitting over time, or over different parts of his body, that are consistent with neural lesions. The diagnosis of MS does not denote the cause of the lesions or of the illness.

Neurotoxicity can injure the nervous system in ways that could mimic probably any neurological or psychiatric disease, including MS. Therefore, all patients with these diseases should be screened for neurotoxic causes of the illness. Screening should examine the constellation of symptoms consistent with neurotoxicity, as well as an occupational and environmental toxic chemical exposure history.

A subject presented with a diagnosis of MS and a history of working for five years at an automobile dealership, located over an abandoned wood-preserving factory. Immediately adjacent to the dealership was an active wood-preserving facility, emitting significant quantities of wood-preserving chemicals and by-products.

Over the years of this employment, the subject's health deteriorated drastically, with neurological and neuropsychological symptoms. Upon careful neuropsychological examination, significant declines in function were detected. These declines were consistent with a neurotoxic effect.

Upon investigation of the site, it was determined that significant quantities of neurotoxic chemicals have been emitted over the years of the subject's employment at the site.

The subject had a neurological event 15 years prior to his employment, which had remitted. Therefore, following these new symptoms, the subject was subsequently diagnosed with MS. Expert neurologists felt that it was likely that new neurological symptoms would not have developed had there not been significant neurotoxic chemical exposure.

Purpose of the study:

To assess neuropsychological function in a man who had chronic, accidental exposure for about five years to wood preserving chemicals from a toxic waste dumpsite and an active wood-preserving facility.


The subject's work site was located on an abandoned wood-preserving factory, designated as a Superfund waste clean-up site. The process generated an estimated 6,000 gallons of crude wood oil and pitch per day for about 60 years. Some of the waste products were stored on the property, part of which was partially paved over after the plant closed to erect an automobile dealership. Toxic substances from the site polluted the local waters and soil. The subject had exposure to these substances during various construction projects on the site, and from vaporization of water and soil contaminants. High levels of arsenic, chromium, phenols and benzene were found in the surface soil.

Adjacent to the dealership is an active wood-preserving facility. Processes used included the chromated copper arsenate (CCA) process, the creosote process, and the pentachlorophenol process. All these processes use and produce neurotoxic substances. The air scrubber was working at zero or less efficiency. The company admitted emitting at least the following neurotoxic substances, in lbs/year: naphthalene (1,000); pentachlorophenol (200); dibenzofurans (100); and creosote (containing toluene, benzene etc.; 250 tons/year), with additional releases of chromium and arsenic. The site, located near a residential area, was widely observed to have frequent noxious odor emissions and uncontrolled dust conditions, with a large number of complaints filed with the state department of environmental regulations.


The subject was a highly successful manager of a new car dealership, with company net profit in the early 1980's of more than a million dollars yearly, and married with children. The dealership had lost money prior to the subject's management. As general manager of the dealership, he worked 10 to 12 hours a day, setting sales records. By all accounts, the subject was known to be quick-witted, assertive, hard-working, strong and very active. He appeared very satisfied with his work, which was quite demanding. In his spare time, 2-3 evenings per week he rebuilt boats, was a certified scuba diver, and took several diving trips with his wife and family.

About two years after arriving at the dealership, the subject began acting erratically in his business decisions and behavior. Decisions took a long time to make, and were frequently rescinded after they were decided. He developed violent mood swings, insomnia and social withdrawal. The dealership started to lose sales and profits, as he was out sick more, arrived late for work and left early. Finally, when he was too weak to come to work, he remained in bed and developed severe vertigo, malnutrition and inability to urinate.

He was taken to the hospital, with symptoms of tingling, double vision, nausea, vomiting, nystagmus, and dysmetria (unable to arrest a muscular movement), and was diagnosed with bilateral cerebellar and right brain stem signs.

Fifteen years prior to this incident, the subject was working in a chemical factory and had developed leg weakness, which improved 90% after leaving that employment, with no re-occurrences. The subject was diagnosed as having multiple sclerosis by neurologists with expertise in that disease. The MRI was interpreted as positive.


Repeated standard neuropsychological testing; extensive collateral interviews; Neurotoxicity Screening Survey; NCV testing; repeated interviews; malingering assessment.

Summary of results:

Neurotoxicity Screening Survey results found symptoms consistent with those of patients diagnosed with neurotoxicity. Repeated neuropsychological testing found a decline in IQ; borderline deficit in visual memory; and deficits in verbal memory, manual dexterity, visuomotor tracking and attention, and logical memory, with mild-moderate depression, and no psychosis or malingering. Nerve conduction velocity assessment showed normal median motor, bilaterally; normal left median sensory response; low amplitude, right median sensory; and abnormal amplitude and dispersion, left sural, with normal right sural.

Conclusion: The signs and symptoms of this subject, which may be consistent with MS, are also consistent with neurotoxicity. As his exposure to neurotoxic chemicals was significant, and his neurological and neuropsychological status was uneventful for 15 years prior to his exposure, it is likely that neurotoxic chemical exposure caused or exacerbated his MS-like condition.

Neurotoxicity-related decline in neuropsychological function was found in this subject presenting with a diagnosis of multiple sclerosis and a history of toxic chemical exposure. In general, some patients with multiple sclerosis may be misdiagnosed, as their condition may be better described as neurotoxically related. This distinction may be important medically as well as forensically.

Patients with neurological disorders such as MS should be advised 1) to not return to work around neurotoxic chemicals, as the exposure may deteriorate their condition; and 2) to guard their environment to reduce unnecessary exposures.

Doctors should investigate possible chemical causes of neurological and neuropsychological conditions. Symptoms consistent with multiple sclerosis actually may be caused by toxic chemical exposure.

Subjects with significant exposure to wood-preserving chemicals should undergo neuropsychological evaluation, particularly if they present with symptoms consistent with neurotoxicity or multiple sclerosis.

Copyright © 1997 Raymond Singer, Ph.D., All rights reserved. No portion of this article may be reproduced without the express written permission of the copyright holder. If you use a quotation, excerpt or paraphrase of this article, except as otherwise authorized in writing by the author of the article you must cite this article as a source for your work and include a link back to the original article from any online materials that incorporate or are derived from the content of this article.

This article was last reviewed or amended on Apr 28, 2015.