Many veterans returning from the Gulf War and other wars have reported experiencing chronic fatigue (McCauley et al. 2002a). Unexplained chronic fatigue, experienced by both the general public and veterans, has been the subject of much discussion by clinicians and researchers alike (Buskila 2000; Straus 1991), but its etiology and course are still unclear. The prevalence of chronic fatigue in the general adult population appears to be less than 2% (Buskila 2000). CDC developed a case definition of chronic fatigue syndrome (CFS), first published in 1988 and revised in 1994 (Box 6-1). It is characterized by the presence of severe fatigue with related functional impairment and the occurrence of at least four of eight other defining symptoms over at least 6 months (Freeman et al. 2005; Fukuda et al. 1994). The most commonly reported symptoms are headache, postexertional malaise, impaired cognition, and muscle pain (Wills et al. 2003). McCauley et al. (2002a) found that 103 of 799 veterans deployed to the Gulf War in 1990-1991 fulfilled the case definition in 1998. The committee notes that fatigue, but not symptoms of fatigue sufficient to meet the CDC definition, is one of the most widely reported symptoms in surveys of Gulf War veterans (Cherry et al. 2001a; Engel et al. 2000; Gray et al. 1999; Ishoy et al. 1999; Kang et al. 2000b; Kelsall et al. 2004a; Simmons et al. 2004; Steele 2000; Unwin et al. 1999).

As in fibromyalgia and chronic pain (discussed later in this chapter), no laboratory tests or pathologic physical signs are widely accepted or provide a definitive diagnosis. The CDC criteria require that three elements be completed as part of a comprehensive evaluation. The first element, determining whether the symptom criteria for CFS are present, requires that a person be queried specifically about length and severity of fatigue and about eight ancillary symptoms. The second, determining whether other medical conditions are present, mandates a complete physical examination, a battery of specified laboratory tests, and a medical history. The third is an assessment of exclusionary conditions (such as lupus, mononucleosis, depression, and multiple sclerosis) (Fukuda et al. 1994; McEwen 2002).

BOX 6-1

Case Definition of Chronic Fatigue Syndrome

CDC criteria for CFS require the presence of both the following:

Clinically evaluated, unexplained persistent or relapsing chronic fatigue that is of new or definite onset (that is, not lifelong), is not the result of ongoing exertion, is not substantially alleviated by rest, and results in substantial reduction in previous levels of occupational, educational, social, or personal activities.

The concurrent occurrence of four or more of the following symptoms: substantial impairment in short-term memory or concentration; sore throat; tender lymph nodes; muscle pain; multi-joint pain without swelling or redness; headaches of a new type, pattern, or severity; unrefreshing sleep; and post-exertional malaise lasting more than 24 hours. These symptoms must have persisted or recurred during 6 or more consecutive months of illness and must not have predated the fatigue.

SOURCE: CDC (2007a).

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