Veterans and Agent Orange Update 2000 (2001) / Chapter Skim
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9 Neurobehavioral Disorders
9 Neurobehavioral Disorders
Pages 440-462
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From page 440... ...
Neurobehavioral difficulties involve two primary categories: cognitive decline, including memory problems and dementia; and neuropsychiatric disorders, including neurasthenia (a collection of symptoms including difficulty concentrating, headache, insomnia, and fatigue) , depression, posttraumatic stress disorder (PTSD)
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From page 441... ...
; cacodylic acid, and picloram and cognitive or neuropsychiatric disorders. The majority of the data that formed the basis for these conclusions came from the Air Force Health Studies (AFHS, 1991, 1995~.
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From page 442... ...
In that follow-up, 870 Ranch Hand veterans and 1,251 comparison subjects received a psychological assessment that consisted of the SCL-90-R and reported psychological disorders that were verified through a medical records review. The verified psychological disorders from the 1997 examination were combined with the verified psychological disorders obtained at baseline, and in 1985, 1987, and 1992.
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From page 443... ...
Moreover, the lack of correlation of these other neuroses with the SCL-90-R a standardized and validated questionnaire that includes scales for anxiety, depression, hostility, interpersonal sensitivity, obsessive-compulsive behavior, paranoid ideation, phobic anxiety, psychoticism, somatization, global severity index, positive symptom total and positive symptom, distress index brings into question the criteria used for the psychological diagnoses. VAO identified that the SCL-90-R, MCMI and related medical outcomes information reported for an earlier AFHS (1991)
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From page 444... ...
In the studies reviewed, pesticide exposure was usually required to occur prior to disease onset, but knowledge of when it occurred in relation to disease onset was not presented. In Update 1998, emphasis on the detection of early-onset parkinsonism was considered vital to test the hypothesis that the disease is related to a toxic exposure because, currently, aging is the only known definitive risk factor for PD.PD becomes clinically apparent when approximately 60 to 70 percent of the neurons in the substantia nigra have deteriorated.
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In a case-control study conducted in Parma, Italy, 68 cases with PD fulfilling the criteria established the UK Parkinson's Disease Society Brain Bank enrolled from the Institute of Neurology were compared for herbicide and pesticide exposure to 86 controls from other outpatient clinics (Smargiassi et al., 1998~. Exposure required either occupational or residential contact for at least ten consecutive years prior to the onset of PD.
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(1991) to examine the risk of PD from pesticide exposure in 19 families with two or more siblings who have PD and a matched comparison group, as well as a second comparison group of 19 sibling pairs with essential tremor.
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Researchers found that patients with PD, past pesticide exposure (>20 days per year in any year of life) , and the presence of the CYP 2D6 29B+ gene had 83 percent predicted probability of PD and dementia.
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From page 448... ...
Conclusions There remains inadequate or insufficient evidence of an association between exposure to the herbicides in this report and motor or coordination dysfunction or Parkinson's disease. In the future, however, as diagnostic accuracy for Parkinson's disease improves, herbicide exposure assessment is quantitated with specific biomarkers, and further research confirms the gene-toxicant interaction in larger prospective studies of PD, this evidence for association may change.
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From page 454... ...
In 1982 a baseline study of 1,208 Air Force Ranch Hands and a comparison group of 1,238 Air Force personnel found no differences between the groups in measures of peripheral nerve function, including neurological symptom evaluation, physical examination, and nerve conduction velocity tests (AFHS,1984~. A follow-up study was conducted in 1985 using the same protocol, except that nerve conduction velocity was not assessed, and once again no differences were seen between groups (AFHS,1987~.
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Other uncontrolled confounders (related to life-style) also might have been involved in the increased incidence of peripheral neuropathy in the Ranch Hand ground crew.
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Also the peripheral nervous system undergoes constant age-related changes that may increase its susceptibility to other metabolic and toxic exposures. Conclusion There remains inadequate or insufficient evidence of an association between exposure to dioxin or the herbicides studied in this report and chronic persistent peripheral neuropathy.
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The committee knows of no evidence that new cases of acute or subacute transient peripheral neuropathy that develop long after service in Vietnam are associated with herbicide exposure. CONCLUSIONS FOR NEUROBEHAVIORAL DISORDERS Strength of Evidence in Epidemiologic Studies As in the earlier reports, this committee finds that there is inadequate or insufficient evidence to determine whether an association exists between exposure to the herbicides used in Vietnam and disorders involving cognitive and neuropsychiatric dysfunction, motor or coordination deficits, and chronic persistent peripheral neuropathy.
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Because of the many species and strain differences in TCDD responses, however, controversy remains regarding the TCDD exposure level that is neurotoxic. Limited information is available on neurotoxic effects of exposure to the herbicides discussed in this report.
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Increased Risk of Disease Among Vietnam Veterans The most recent Air Force Health Study (AFHS, 2000) reported differences in prevelance of peripheral neuropathy between the Ranch Hand and comparison group, but the clinical relevance is not clear.
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1990. Parkinson's disease: a case-control study of occupational and environmental risk factors.
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1997. Environmental risk factors and Parkinson's disease: a case-control study in Taiwan.
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1991. Environmental risk factors in siblings with Parkinson's disease.
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