Definition
Chronic fatigue and chronic fatigue syndrome: shifting boundaries and attributions

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Abstract

The subjective symptom of “fatigue” is one of the most widespread in the general population and is a major source of healthcare utilization. Prolonged fatigue is often associated with neuropsychological and musculoskeletal symptoms that form the basis of several syndromal diagnoses including chronic fatigue syndrome, fibromyalgia, and neurasthenia, and is clearly not simply the result of a lack of force generation from the muscle. Current epidemiologic research in this area relies predominantly on self-report data to document the prevalence and associations of chronic fatigue. Of necessity, this subjective data source gives rise to uncertain diagnostic boundaries and consequent divergent epidemiologic, clinical, and pathophysiologic research findings. This review will highlight the impact of the case definition and ascertainment methods on the varying prevalence estimates of chronic fatigue syndrome and patterns of reported psychological comorbidty. It will also evaluate the evidence for a true postinfective fatigue syndrome.

Section snippets

Prevalence of chronic fatigue and chronic fatigue syndrome

When utilizing self-report surveys, the measurement of fatigue in the community hinges closely on the interpretation of particular words and their connotations in the questionnaires completed by respondents.3 For example, after excluding subjects with symptoms attributable to medication or recognized medical disorder, the Epidemiologic Catchment Area (ECA) study demonstrated a 14% community prevalence of “feeling tired out,” compared with 2.2% for “feeling weak.”1 In this context, the specific

Chronic fatigue syndrome and other fatigue-related syndromes

A natural consequence of these difficult diagnostic boundaries is overlap with other similar syndromal disorders, notably those that share fatigue as a major symptom. The list of such conditions is long, but notably includes fibromyalgia, irritable bowel syndrome, neurasthenia, multiple chemical sensitivity syndrome, sick building syndrome, as well as depressive and anxiety disorders.

The overlap between chronic fatigue syndrome and fibromyalgia, for example, has been specifically examined.

Chronic fatigue syndrome and psychological comorbidity

The relation of the chronic fatigue syndrome to the syndrome of major depression is also paramount. Neuropsychologic complaints such as concentration difficulties, memory impairment, sleep disruption, and mood disturbance are almost universal in patients with chronic fatigue syndrome, and concurrent psychiatric diagnoses (predominantly depression or anxiety) can be made in a substantial proportion of cases.26, 27, 28 This high degree of comorbidity with depression is, in part, an artefact of

The validity of a postinfective fatigue syndrome

The potential role of infectious agents in producing chronic fatigue has been a strongly favored hypothesis. This notion arose naturally from the historical observations linking specific infections such as brucellosis to a subsequent fatigue state. Further support for this possibility comes from the anecdotal histories that patients with chronic fatigue syndrome give and the attributions made to the prior events by physicians. These recollections typically describe a “flu-like” illness

Conclusions

Interpretation and comparison of the results of epidemiologic studies evaluating chronic fatigue and chronic fatigue syndrome should be undertaken only after careful consideration of: (1) the survey instrument (i.e., the questionnaire) and methodology (e.g., self-report alone versus physician assessment); (2) the setting from which cases are identified (community surveys versus primary care, or tertiary referral practice); and (3) the case definition utilized. Even after these key factors have

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