specifically examine insecticide exposure but focused on the broader category of “pesticides.” The occupational studies reviewed used occupations as surrogates for exposure, but the committee was unable to determine whether exposure relevant to the Gulf War had occurred.

The committee concludes, from its assessment of the epidemiologic literature, that there is inadequate/insufficient evidence to determine whether an association exists between exposure to the insecticides under review and Alzheimer’s disease.

SOLVENTS AND NEUROLOGIC DISEASES

This section addresses the association between exposure to solvents and four neurologic diseases: Parkinson’s disease, amyotrophic lateral sclerosis, multiple sclerosis, and Alzheimer’s disease. Those diseases have distinct sex and age distributions and pose numerous challenges to epidemiologic research, such as diagnostic uncertainty, presumed long latency, and concern about the reliability of self-reported exposure information from patients with cognitive impairment or inability to communicate. The committee evaluated the body of evidence on solvent exposure and neurologic disorders almost exclusively from case-control studies. The design of the studies is inherently subject to a number of potential biases, some of which cannot be avoided. Those limitations are described in the context of each study that the committee evaluated.

Parkinson’s Disease and Solvent Exposure: Epidemiologic Studies

PD is described earlier in this chapter. The committee evaluated studies only with PD as the outcome measure rather than the more generic diagnosis of parkinsonism, as explained earlier. Only two studies were found to be sufficiently rigorous in design to be useful in providing evidence on the relationship between solvent exposure and PD (Hertzman et al., 1994; Seidler et al., 1996). One of them (Hertzman et al., 1994) focused on pesticides and presented little pertaining to solvent exposure. Both were case-control studies that used prevalent cases (Table 7.9).



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