BOX 4-1

CDC Case Definition of Chronic Fatigue Syndrome

A diagnosis of chronic fatigue syndrome requires the presence of both the following:

  • Clinically evaluated, unexplained, persistent or relapsing chronic fatigue that is of new or definite onset (that is, has not been lifelong), is not the result of ongoing exertion, is not substantially alleviated by rest, and results in substantial reduction in levels of occupational, educational, social, or personal activities. Clinical evaluation includes medical history, physical examination, laboratory studies, and psychiatric assessment.

  • Concurrent occurrence of four or more of the following, which must have persisted or recurred during 6 or more consecutive months of illness and must not have predated the fatigue: self-reported impairment of short-term memory or concentration severe enough to cause substantial reduction in levels of occupational, educational, social, or personal activities; sore throat; tender cervical or axillary lymph nodes; muscle pain; multijoint pain without joint swelling or redness; headaches of a new type, pattern, or severity; unrefreshing sleep; and postexertional malaise lasting more than 24 hours.

SOURCE: Fukuda et al. (1994).

large, population-based design, stratified sampling method, analysis of participation bias, comprehensive examination, and use of computer-based algorithms by researchers who were blinded to deployment status. Study limitations include demographic differences between the deployed and nondeployed cohorts and the relatively low rate of participation in the study.

Secondary Studies

An earlier questionnaire study, conducted during phase I of the VA study, surveyed 11,441 deployed and 9476 nondeployed veterans (Kang et al., 2003). Several items in the 48-item symptom questionnaire served as the basis for meeting the case definition for CFS. After exclusion of veterans who self-reported medical conditions that could explain their fatigue, 4.9% of deployed and 1.2% of nondeployed veterans (OR 4.2, 95% CI 3.3-5.5) met the case definition. The investigators found that CFS was not related to the severity of combat stressors. The latter was assessed according to responses to questions on wearing chemical protective gear or hearing chemical alarms, being involved in direct combat duty, or witnessing any deaths. The study was limited by its reliance on solely self-reported symptoms without a physical or laboratory examination and on self-reported physician-diagnosed conditions. Those shortcomings resulted in a higher rate of CFS-like illness than was observed when the same cohorts were sampled and underwent more rigorous medical evaluations as in Eisen et al. (2005).

Proctor and colleagues (2001b) conducted in-person interviews of 180 Army veterans selected from the larger Fort Devens cohort to determine the prevalence of CFS. The deployed veterans were compared with 46 members of an air ambulance company deployed to Germany during the Gulf War. The prevalence was determined according to the symptom criteria specified by the CDC case definition (Fukuda et al., 1994). With that approach, the rate was higher in the Gulf War deployed than the Germany deployed group (7.5% vs 0%, p = 0.02). When additional information from self-reported medical or psychiatric conditions (such as substance abuse and bipolar disorder) and clinical psychiatric interviews was considered, the prevalence in Gulf War veterans decreased to 2%, which was no longer significant. The study demonstrated the importance of performing psychiatric assessments, but it was limited by the relatively small sample and the lack of medical or laboratory evaluations.

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