A later study by VA researchers (Blanchard et al. 2006) sought to determine the prevalence of unexplained illnesses in the VA study. This study was not a factor analysis itself but applied CDC’s definition of chronic multisymptom illness, which had been derived in part by factor analysis (Fukuda et al. 1998), to determine its prevalence. The Fukuda et al. study also provided prevalence figures, but because of its nonrepresentative sample, the committee considered it a secondary study. The VA investigators first assessed veterans’ responses to the 47 symptom questions. Participants were asked about symptoms in face-to-face interviews 10 years after the war. Several other publications resulting from VA's study are discussed elsewhere in this volume (for example, Eisen et al. 2005). Participants who reported one or more symptoms from each of three clusters (fatigability, mood and cognition, and musculoskeletal) were considered to meet the case definition.15 Cases were classified as severe if at least one symptom in each cluster was rated as severe. The investigators found that overall 29% of deployed participants met the criteria for chronic multisymptom illness as opposed to 16% of nondeployed participants. Severe chronic multisymptom illness was found in 7% of deployed veterans and 1.6% of nondeployed veterans. Among deployed veterans a higher score on the Combat Exposure Scale was associated with chronic multisymptom illness. Among nondeployed veterans, female sex, less than a college education, and a higher score on the Combat Exposure Scale were associated with chronic multisymptom illness. Deployed veterans who met the case definition had lower mean scores on the SF-36 for physical and mental health, more nonroutine clinic visits and a higher mean number of prescriptions, and they were more likely to be using psychotropic medications. Chronic multisymptom illness in both deployed and nondeployed veterans was more likely to be associated with fibromyalgia syndrome, CFS, symptomatic arthralgias, dyspepsia, the metabolic syndrome, PTSD, anxiety disorders, major depression, nicotine dependence, and more than one psychiatric diagnosis during the year preceding the examination but, with the exception of CFS, was no more likely to be associated with deployment than with nondeployment. The report was based on the same cohort as Fukuda et al. and had the same problems of low participation rates and self-reporting of symptoms. Nonetheless, it provides evidence that the cluster of symptoms previously studied by Fukuda et al. also existed in this group and 10 years after the Gulf War was twice as common in participants who had been deployed as in those who had not been.

The Iowa Cohort

The Iowa study (Iowa Persian Gulf Study Group 1997) was the first major population-based study to group symptoms into categories suggestive of existing syndromes or disorders, such as fibromyalgia or depression. Its finding of a considerably higher prevalence among Gulf War veterans of symptom groups suggestive of fibromyalgia, depression, and cognitive dysfunction motivated the first applications of factor analysis to group and classify veterans’ symptoms. Several years later, the same team of Iowa investigators performed a factor analysis on the Iowa cohort (Doebbeling et al. 2000). They studied the frequency and severity of 137 self-reported symptoms among 1,896 Gulf War veterans and 1,799 veterans who had not been deployed. They randomly divided the Gulf War veterans into two groups that they called the derivative sample and the validation sample. They identified three symptom factors in deployed veterans in the derivative sample that accounted for 35% of the variance: somatic distress (joint

15

Persistent fatigue for at least 24 hours after exertion was the single symptom in Cluster A (fatigability). Feeling depressed; feeling irritable; difficulty in thinking or concentrating; feeling worried; tense, or anxious; problems in finding words; and problems in going to sleep were the symptoms included in Cluster B (mood and cognition). Joint pain and muscle pain were the two symptoms included in Cluster C (musculoskeletal).



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