Gulf War unexplained illnesses: Persistence and unexplained nature of self-reported symptoms

Most published reports of health symptoms among Gulf War (GW) veterans have been based on self-reported questionnaire data. The presence of these symp toms at the time of a clinical evaluation and the unexplained nature of the symptoms have not been described. We report the findings of a sample of sy mptomatic veterans that were examined as part of a population-based case-co ntrol study of GW unexplained illnesses. Participants in the case-control s tudy were selected from responders to a cross-sectional survey of a random sample of GW veterans residing in the northwestern United States. The initi al survey questionnaire solicited information on the presence of fatigue an d psychological/cognitive, gastrointestinal, musculoskeletal, and dermatolo gical problems, The persistence of the symptoms and possible explanatory di agnoses were explored at the time of the clinical evaluation. Findings from the first 225 participants who completed clinical examinations indicate si gnificant differences between self-reported symptoms on the survey question naire and those confirmed at the time of clinical exam. The agreement betwe en symptoms reported both on the survey and at the time of examination vari es across the symptom groups. While self-reported unexplained fatigue was c onfirmed at the time of clinical encounter in 79% of participants, self-rep orted gastrointestinal symptoms were confirmed at the clinical encounter in only 20% of participants, Differences between symptoms reported on the sur vey questionnaire and those confirmed at the time of clinical encounter wer e attributable to finding a clinical diagnosis for the symptom, resolution of symptom(s) between time of questionnaire and clinical exam, and inadvert ent endorsement of the symptom on the questionnaire. These findings suggest that due to the possibility of outcome misclassification, inappropriate co nclusions may be drawn about the association between exposures and unexplai ned illnesses in GW veterans from data derived solely from self-administere d questionnaires. (C) 1999 Academic Press.