Considerations for Designing an Epidemiologic Study for Multiple Sclerosis and Other Neurologic Disorders in Pre and Post 9/11 Gulf War Veterans (2015) / Chapter Skim
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BRIEF REPORT ON CONSIDERATIONS OF DESIGNING AN EPIDEMIOLOGIC STUDY FOR NEUROLOGIC DISORDERS
BRIEF REPORT ON CONSIDERATIONS OF DESIGNING AN EPIDEMIOLOGIC STUDY FOR NEUROLOGIC DISORDERS
Pages 1-22
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data. Results: In examining the burden of illnesses, the committee found that the existing data suggest that Gulf War deployed veterans do not have a higher prevalence of the diseases of interest than the nondeployed Gulf War veterans, with the exception of headache and migraine.
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Other neurologic diseases to be considered include Parkinson's disease and brain cancers, as well as central nervous system abnormalities that are difficult to precisely diagnose. The committee will identify its data needs, request those data from the Department of Veterans Affairs, and will analyze the data.
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BURDEN OF ILLNESS This section describes findings from VA utilization reports, Armed Forces Health Surveillance Center (AFHSC) reports, and studies of neurologic outcomes (specifically, MS, migraine, Parkinson's disease, and brain cancers)
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The odds of having at least one primary diagnostic code of MS is statistically significantly lower for deployed 19901991 Gulf War veterans compared with nondeployed veterans (odds ratio [OR] = 0.90, 95% confidence interval [CI]
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A total of 1,841 incident cases of MS and ODD were identified: 387 cases among the 696,118 deployed and 1,454 cases among the 1,786,215 nondeployed veterans. The RR of MS was statistically significantly lower in the deployed compared with the nondeployed (RR = 0.69, 95% CI: 0.610.78)
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. Of those deployed and nondeployed veterans using VA health care services, a primary diagnostic code of migraine (ICD-9-CM: 346)
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. Combat-deployed service members had statistically significantly higher adjusted odds of new-onset headache disorder than nondeployed (OR = 1.72, 95% CI 1.55-1.90 for men; OR = 1.84, 95% CI 1.55-2.18 for women)
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, entered by any provider during an inpatient or outpatient encounter, was listed for 403 deployed and 487 nondeployed veterans; however, a diagnosis of Parkinson's disease was not confirmed. The odds of having a primary diagnosis of Parkinson's disease or paralysis agitans were statistically significantly lower for Gulf War deployed veterans compared with nondeployed veterans (OR = 0.78, 95% CI: 0.68-0.89)
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, entered by any provider during an inpatient or outpatient encounter, was listed for 342 deployed and 332 nondeployed veterans. The crude odds of having a primary diagnosis of malignant brain cancer were not statistically different for deployed compared with nondeployed Gulf War veterans (OR = 0.97, 95% CI: 0.83-1.13)
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The study did not find an excess proportion of brain cancer cases among deployed compared with era veterans. The number of brain cancers in the Gulf War deployed veterans was 278 and 410 in era veterans.
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Although the algorithm was validated using records from a managed care organization, the fields most strongly associated with migraine case status are also collected in patient health records and VA administrative databases. A sample of 8,579 eligible enrollees (between the ages of 18 and 55, continuously enrolled in the health plan for 24 months, and had at least one medical encounter in a 12-month period)
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When the presence of a Parkinson's disease prescription was added to this algorithm, sensitivity decreased to 77.1%, specificity increased to 68.1%, positive predictive value increased to 88.2%, and negative predictive value decreased to 49%. These algorithms yielded improved parameters over using a single occurrence of a Parkinson's disease diagnostic code in the medical record.
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Cox proportional hazard models were used to calculate RR estimates between deployed and nondeployed veterans. An alternative method to using mortality data to study the incidence of brain cancer among deployed and nondeployed Gulf War veterans is through the use of linked cancer registry data.
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Because malignant brain cancers are fatal and usually occur within a relatively short timeframe, death records combined with VA administrative data can accurately identify malignant brain cancers and be used to estimate both incidence and prevalence. In contrast, mortality data are not a good proxy for estimating MS, Parkinson's disease, or migraine incidence or prevalence as these illnesses are chronic and usually not the primary cause of death.
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VA assembled a cohort of 621,902 deployed Gulf War veterans and a random sample of 746,248 era veterans that could be used and would allow for an adequately powered study to determine whether deployment is associated with an increased risk of developing any of the four neurologic conditions of interest. However, it is not easy to select a comparison group for OEF/OIF/OND active-duty service members because as of December 2011, a majority of members8 in each service branch deployed at least once to Iraq or Afghanistan (RAND, 2013)
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The DOD database identified 100% of OEF and OIF women veterans, whereas the VHA National Enrollment Database identified only 23.5% and the VBA databases identified 13.7% of that group. Although combining all of those administrative datasets expanded the representativeness of the population of veterans for inclusion in research, it still captured only 51.4% of the total population of living women veterans (including 43% who were non-VA users)
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. The limited information collected by the surveys and unconfirmed responses for MS, Parkinson's disease, and brain cancer questions limit the usefulness of those surveys for use in an epidemiologic study to determine the incidence or the prevalence of the conditions named in the legislation.
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. Although more information was collected on headaches and migraines than the other conditions of interest, the questions included in the survey were not from validated screens and the information was not validated using medical records or clinical exams.
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Of those deployed and nondeployed Gulf War veterans using VA health care services, a primary diagnostic code of Parkinson's disease was listed for 403 deployed and 487 nondeployed veterans. The odds of having a primary diagnosis of Parkinson's disease were statistically significantly lower for Gulf War deployed veterans compared with nondeployed veterans (OR = 0.78, 95% CI: 0.68-0.89)
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VA utilization data noted 342 malignant brain cancers in Gulf War deployed veterans and 332 in nondeployed veterans among those using VA health care. The odds of having a primary diagnosis of malignant brain cancer were not statistically different for deployed compared with nondeployed Gulf War veterans (OR = 0.97, 95% CI: 0.83-1.13)
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, inaccurate diagnoses, and assigning codes prematurely or for uncertain diagnoses. Accurately identifying disease onset or incidence without extensive records review or interviewing subjects is difficult for MS and Parkinson's disease.
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Furthermore, VA and numerous other researchers have already published results on the outcomes of concern using VA data linked to other data sources (e.g., CDC mortality data, DOD) , and therefore, it is unlikely that the committee would find different results from those well-designed studies that already have been published and scrutinized (e.g., brain cancer studies by Barth et al.
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