deployed veterans but had intentionally recruited veterans who experienced a high prevalence of post-Gulf War illness (Hom et al. 1997). That study failed to adjust for key confounders and for the large number of statistical comparisons in their study, raising doubt about the validity of their findings.

In conclusion, primary studies of deployed Gulf War veterans vs non-Gulf War deployed do not demonstrate differences in cognitive and motor measures as determined through neurobehavioral testing. However, returning Gulf War veterans with at least one symptom commonly reported by Gulf War veterans (such as, fatigue, memory loss, confusion, inability to concentrate, mood swings, somnolence, GI distress, muscle and joint pain, or skin or mucous membrane complaints) demonstrated poorer performance on cognitive tests when compared to returning veterans who did not report such symptoms.

Several studies focused on multisymptom-based medical conditions: fibromyalgia, CFS, and MCS. Those conditions have several features in common: they do not fit a precise diagnostic category; case definitions are symptom-based; there are no objective criteria for validating the case definitions; and the symptoms among those syndromes overlap to some extent. Gulf War-deployed veterans report higher rates of symptoms that are consistent with case definitions of MCS, CFS, and fibromyalgia.

Several large or population-based studies of Gulf War veterans found, by questionnaire, that prevalence of MCS-like symptoms ranged from 2% to 6% (Black et al. 1999; Black et al. 1999; 2000; Black et al. 2000; Goss Gilroy Inc. 1998; Goss Gilroy Inc. 1998; Goss Gilroy Inc. 1998; Reid et al. 2001; Unwin et al. 1999). Most studies found that the prevalence in Gulf War veterans was about 2-4 times higher than that in nondeployed veterans. However, no two of the primary studies used the same definition of MCS, so it is difficult to compare them, and none performed medical evaluations to exclude other explanations as would be required by the case definition of MCS.

The prevalence of CFS among Gulf War veterans is highly variable from study to study; most studies used the Centers for Disease Control and Prevention case definition. One primary study (Eisen et al. 2005) demonstrated a higher prevalence of CFS in deployed than in nondeployed veterans (odds ratio [OR] 40.6, 95% confidence interval [CI] 10.2-161.15).

Secondary studies also showed a higher prevalence of CFS and CFS-like illnesses among veterans deployed to the Persian Gulf than among their counterparts who were not deployed or who were deployed elsewhere.

The diagnosis of fibromyalgia is based on symptoms and a very limited physical examination that consists of determining whether pain is elicited by pressing on several points on the body; there are no laboratory tests with which to confirm the diagnosis. Only one of the available cross-sectional studies, Eisen and colleagues (2005), included both Gulf War-deployed and nondeployed veterans and used the full American College of Rheumatology (ACR) case definition of fibromyalgia, including the physical-examination criteria (other studies used a case definition based on symptoms alone). That study found a statistically significant difference in the prevalence of fibromyalgia between deployed and nondeployed veterans (2.0% vs 1.2%; adjusted OR1, 2.32; 95% CI, 1.02- 5.27). The study by Smith and colleagues (2000) found no association between Gulf War deployment and hospitalization for fibromyalgia, but the committee did not find this to be inconsistent with the positive findings in the Eisen et al. study because very few cases of fibromyalgia are severe enough to warrant hospitalization (notably,

1

Adjusted for differences in age, sex, race, years of education, smoking, type of duty, service branch, and rank.



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