Veterans and Agent Orange Health Effects of Herbicides Used in Vietnam (1994) / Chapter Skim
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10 Neurobehavioral Effects
10 Neurobehavioral Effects
Pages 640-671
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From page 640... ...
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 641... ...
For example, body temperature can modify EMG data, examiner style and native intelligence can affect patient performance on neuropsychologic tests, and fatigue or medications can profoundly affect EEG patterns. For these reasons, rigorous methodology and maximally matched control or comparison populations are especially important for the scientific study of the causes of neurologic and behavioral alterations.
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From page 642... ...
In approaching this study of the health effects of herbicide exposure, the committee discussed meta-analysis for certain health outcomes with consideration of sample size, measurement of exposure as well as outcome, selection of controls, period of observation, and other methodologic factors. For neurobehavioral disorders, however, a sufficient number of studies of neurological disorders with similar exposure classifications and disease outcome diagnostic groups were not available for this type of analysis.
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From page 649... ...
each differed significantly from published norms. Production workers differed on 9 of 13, and administrative staff on 6 of 13, clinical scales.
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From page 650... ...
, and other subjective necrologic complaints have appeared frequently in case studies and some cohort reports, but studies with comparison populations have not regularly suggested CNS problems. In a cohort mortality study of 1,222 male Canadian forestry workers at an electrical utility presumed to have been exposed to 2,4-D and 2,4,5-T (Green, 1991)
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From page 651... ...
Considered in the analysis were the following covariates: age, race, income, education, family history of psychiatric disorders, current treatment for psychiatric disorders, current treatment with neurotoxic drugs or drugs that can produce depression as a side effect, history of head injury, history of low vertebral disk herniation, history of chronic medical disorders, self-reported occupational exposure to neurotoxicants, self-reported exposure to Agent Orange during military service in Vietnam, smoking history, and lifetime alcohol use. Workers had a mean serum TCDD level of 220 parts per trillion (ppt)
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From page 652... ...
This subtest is a good estimate of premorbid level of verbal intelligence, which significantly influences performance on neurobehavioral tests (Bolla-Wilson and Bleeker, 1986~. Group differences on the Vocabulary subtest indicate that the control and exposed groups were not comparable on this confounding variable, and no statistical adjustments were used to control for the possible confounding effects.
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From page 653... ...
Vietnam Veterans Studies As with environmental disasters, neurotoxicant studies conducted on war victims are confounded by the stress of the war experience. For many centuries it has been well recognized that catastrophes, personal tragedies, and armed conflict lead to a variety of somatic and psychologic symptoms.
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From page 654... ...
Active cases of chloracne were used to estimate Agent Orange exposure. The groups were matched on age, education, and period of Vietnam service.
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From page 655... ...
examined the postservice mortality of a cohort of 9,324 Army Vietnam veterans compared to 8,989 Vietnam era Army veterans who did not serve in Vietnam. In the first five years after discharge, Vietnam veterans had a 17 percent higher mortality rate than Vietnam era veterans and most deaths were from external causes (e.g., motor vehicle accidents, drug and alcohol use)
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From page 656... ...
A poor measure of herbicide exposure could also lead to a lack of apparent differences; problems with self-reported exposures and the use of current serum TCDD levels to estimate prior dioxin exposure are discussed in Chapter 6. Serum TCDD concentrations from 888 participants in Operation Ranch Hand were compared to those of 856 Air Force veterans who did not participate in Ranch Hand (AFHS, 19911.
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From page 657... ...
To maximally define the direct effects of herbicides and dioxin on cognitive and neuropsychiatric function, future studies should focus primarily on occupationally exposed groups for whom levels of exposure are better known and neurobehavioral testing can be conducted in relative proximity to the time of exposure. Based on past findings, if herbicide or TCDD exposure is associated with neurobehavioral disorders, these are in all likelihood subtle.
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From page 658... ...
Using chloracne as a clinical measure of TCDD exposure, one study found that strokes occurred more frequently than expected in chloracne subjects compared to nonchloracne subjects (RR = 3.8, CI 1.8-12.1; Bond, 1987~. This risk estimate, however, was based on only four cases, and multiple chemical exposures were likely.
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From page 659... ...
In the 1987 follow-up examination, coordination difficulty and postural tremor reportedly occurred more frequently in Ranch Hands (AFHS, 1990~. This clinical finding was reinforced in the serum TCDD analysis of the 1987 examination data; Ranch Hands with elevated serum TCDD levels experienced more coordination difficulties than the comparison group (AFHS, 1991~.
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From page 660... ...
One study found that children whose fathers reported exposure to Agent Orange in Vietnam scored significantly worse on a variety of sensory integrative function tests. Because of the small number of subjects and the lack of distinction between Vietnam service and specific TCDD exposure, it is not possible to determine whether herbicide exposure was associated with the test scores (Becker, 19824.
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From page 661... ...
Furthermore, since the laboratory workers had insidious onset of parkinsonism, chronic exposure could be associated with the problem, without a massive accident or evidence of acute intoxication (Langston and Ballard, 1983~. As Vietnam veterans move into the decades when Parkinson's disease becomes more prevalent, attention to the frequency and character of new cases of parkinsonism in exposed versus nonexposed individuals may be highly useful in assessing whether dioxin or herbicide exposure is a risk factor for eventual Parkinson's disease.
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From page 662... ...
A necrologic evaluation of a smaller group of 90 volunteers was not specifically described, but the workers with chloracne experienced significantly more symptoms of muscle pains, decreased libido, and erection/ejaculation difficulties than the nonchloracne subjects. Furthermore, 18.3 percent of chloracne subjects, compared to none of the controls, had decreased pin sensation (p < .01~.
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From page 663... ...
Serum TCDD levels were not associated with the incidence of peripheral neuropathy. Environmental Studies Major environmental disasters in Seveso, Italy, and Missouri have served as sources for study of the necrologic effects of TCDD exposure.
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From page 664... ...
compared 308 Seveso residents with 305 nonexposed residents from nearby towns. The authors found no increased risk of peripheral neuropathy among the exposed residents.
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From page 665... ...
There were more symptoms of peripheral neuropathy reported among Vietnam veterans than among nonVietnam veterans, but there was no increased objective evidence of peripheral neuropathy (CDC, 1988~. Summary of Peripheral Nervous System Disorders Although many case reports suggest that an acute or subacute peripheral neuropathy can develop with exposure to TCDD and related chemicals, reports with comparison groups do not offer clear evidence that TCDD exposure is associated with chronic peripheral neuropathy.
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From page 666... ...
Conclusions for Peripheral Nervous System Disorders Strength of Evidence in Epidemiologic Studies There is inadequate or insufficient evidence to determine whether an association exists between exposure to herbicides* (2,4-D; 2,4,5-T and its contaminant TCDD; cacodylic acid; and picloram)
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From page 667... ...
1986. Wisconsin Vietnam Veteran Mortality Study: Proportionate Mortality Ratio Study Results.
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From page 668... ...
1989a. Comparison of Serum Levels of 2,3,7,8-Tetrachlorodibenzop-dioxin with Indirect Estimates of Agent Orange Exposure among Vietnam Veterans: Final Report.
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From page 669... ...
1991. A cohort mortality study of forestry workers exposed to phenoxy acid herbicides.
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From page 670... ...
1988. Agent Orange exposure and posttraumatic stress disorder.
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From page 671... ...
In press. Peripheral neuropathy after occupational exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)
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