FIGURE D.1 General steps of disease recognition.

diagnoses that are often similar. Case definitions are usually the product of expert panels weighing the relevant body of research, which may include quantitative techniques such as factor analysis (Ismail et al., 1999). For example, several case definitions have been developed for Gulf War illnesses on the basis of factor analysis (Haley et al., 1997; Fukuda et al., 1998), yet none has gained strong acceptance, due either to methodological limitations or to lack of specificity (i.e., the inability to distinguish sufficiently between deployed versus nondeployed veterans). More refined case definitions are likely to emerge in light of ongoing research, and these are likely to elicit intense scrutiny. The discovery of a biological marker would likely prove decisive, as some researchers point out that a unique syndrome cannot be teased apart solely from veterans’ symptoms (Ismail et al., 1999). The point is that existing knowledge of veterans’ unexplained illnesses has not yielded a case definition that successfully specifies a new syndrome. That is why the prevailing medical convention is to resist the popular label “Gulf War syndrome.”

When evidence is presented that a case definition is successful at singling out a new patient population from comparison groups, the case definition progresses a step forward: it begins to achieve recognition by the medical establishment as a new syndrome. The term “syndrome” is by convention reserved for a reproducible set or cluster of symptoms, signs, and/or laboratory tests, without known pathology or etiology (Scadding, 1996). The identification and labeling of a new syndrome is not, according to the medical model, an end in

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