To approach its task, the committee first developed a working definition of CMI. It began by considering the CDC definition described above. Fukuda et al. (1998) arrived at their case definition for CMI by using both a statistical approach called factor analysis and a clinical approach in which symptoms had to be reported for at least 6 months by at least 25% of 1991 Gulf War Air Force veterans enrolled in the study and by deployed veterans at least 2.5 times more often than by nondeployed military personnel. Three categories of symptoms were included in their case definition: fatigue, mood and cognition, and musculoskeletal. Other types of reported symptoms— including gastrointestinal, respiratory, and neurologic—did not meet the threshold for the case definition. The committee decided to broaden its working definition to include respiratory, gastrointestinal, and neurologic symptoms because previous IOM reports found that these types of symptoms were commonly reported by 1991 Gulf War veterans (IOM, 2006, 2010). As suggested in the 1995 IOM report Health Consequences of Service During the Persian Gulf War: Initial Findings and Recommendations for Immediate Action, a reasonable case definition of CMI is necessary for VA hospitals to identify veterans who are eligible for care for their symptoms (IOM, 1995). Correctly identifying a health condition may improve patient care and avoid unnecessary tests (Wegman et al., 1997).

CMI is a complex, amorphous condition and its case definition may change as new scientific information emerges. For the purpose of this report, the committee defined CMI as follows:

The presence of a spectrum of chronic symptoms experienced for 6 months or longer in at least two of six categories—fatigue, mood and cognition, musculoskeletal, gastrointestinal, respiratory, and neurologic—that may overlap with but are not fully captured by known syndromes (such as IBS, CFS, and fibromyalgia) or other diagnoses.

It is important to note that the committee’s definition does not include syndromes that have well-defined diagnostic criteria, such as IBS, CFS, and fibromyalgia. However, because of the shared symptoms, effective therapies for those defined syndromes may be beneficial to patients who have CMI. Chapter 5 of this report explores the evidence that supports therapies for the other syndromes and discusses the possible application of the therapies for managing CMI.

As discussed in Chapter 7, the Department of Veterans Affairs (VA) provides disability compensation for CMI associated with Gulf War service without regard to cause (38 CFR Sec. 3.317).

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