chemical sensitivity (MCS). However, the case definitions for those conditions are based on symptom reports, and there are no objective diagnostic criteria that can be used to validate the findings, so it is not clear whether the literature supports a true excess of those conditions or whether the associations are spurious and result from the increased reporting of symptoms across the board. The literature also demonstrates that deployment places veterans at increased risk for symptoms that meet diagnostic criteria for a number of psychiatric illnesses, particularly posttraumatic stress disorder (PTSD), anxiety, depression, and substance abuse. In addition, comorbidities have been reported, for example, veterans reporting symptoms of both PTSD and depression. The committee felt confident that several studies validated the increased risk of psychiatric disorders.

Some studies indicate that Gulf War veterans are at increased risk for amyotrophic lateral sclerosis (ALS). With regard to birth defects, there is weaker evidence that Gulf War veterans’ offspring might be at risk for some birth defects; the findings are inconsistent. Finally, long-term exacerbation of asthma appeared to be associated with oil-well fire smoke, but there were no objective measures of pulmonary function in the studies.

The health outcomes presented above are discussed in some detail in the following pages. They are grouped according to whether the findings were based primarily on self-reporting of symptoms or on objective measures and diagnostic medical tests.

Outcomes Based Primarily on Symptoms and Self-Reports

The largest and most nationally representative survey of US veterans found that nearly 29% of deployed veterans met a case definition of “multisymptom illness”, compared with 16% of nondeployed veterans (Blanchard et al. 2006). Those figures indicate that unexplained illnesses are the most prevalent health outcome of service in the Gulf War. Several researchers, using factor or cluster analyses, have tried to determine whether or not the symptoms that have been reported by Gulf War veterans cluster in such a way as to make up a unique syndrome, such as “Gulf War Illness”.

Numerous studies (Cherry et al. 2001; Doebbeling et al. 2000; Everitt et al. 2002; Forbes et al. 2004; Kang et al. 2002) have used statistical techniques, such as factor and cluster analyses to search for such symptom clusters or syndromes. Those studies have demonstrated that deployed veterans report more symptoms and more severe symptoms than their nondeployed counterparts, but they did not find a unique symptom complex (or syndrome) in deployed Gulf War veterans. What those studies have found is a global increase in symptoms reported by Gulf War-deployed veterans compared to their counterparts—global in that the increased symptom rates occur in every category of health outcome.

Among the many symptoms reported by Gulf War veterans are deficits in neurocognitive ability. Obviously such reports are of concern because of the potential for those deficits to have adverse effects on the lives of the veterans. Primary studies found nonsignificant trends of poorer neurobehavioral performance when Gulf War veterans were compared to nondeployed veterans or veterans deployed to Germany. However, when PTSD (White et al. 2001) or depressed mood (David et al. 2002) was treated as a confounder in the statistical analyses those trends disappeared, but that adjustment might be inappropriate because of the possibility of overcontrolling a variable that might lie on the causal pathway.

One study concluded that Gulf War veterans who reported symptoms associated with the Gulf conflict performed more poorly on neurobehavioral tests than veterans who did not report symptoms (Storzbach et al. 2000); another study found substantial neurobehavioral deficits in



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