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Chronic fatigue syndrome—a clinically empirical approach to its definition and study

Reeves WC, Wagner D, Nisenbaum R, Jones JF, Gurbaxani B, Solomon L, Papanicolaou DA, Unger ER, Vernon SD, Heim C
Chronic fatigue syndrome - a clinically empirical approach to its definition and study
BMC Medicine 3:19, 2005 The complete electronic version of this article is available at http://www.biomedcentral.com/1741-7015/3/19

Summary

Chronic fatigue syndrome ( CFS) was first formally defined in 1988 by CDC. An Australian case definition was published in 1990, and a third case definition (from the United Kingdom) was published in 1991. In 1994 an international collaborative group, which included authors of earlier case definitions, published the current CFS case definition. These international consensus criteria for the diagnosis of CFS have been pivotal to recognition of the disorder as a major public health problem and have encouraged the systematic investigation of risk factors, diagnostic markers, and management of CFS. The criteria have been used extensively by investigators around the world and have supported substantial advances in understanding the epidemiology and clinical aspects of CFS. However, reproducible biomarkers have not been found for CFS, and its pathophysiology remains undefined. This reflects, in part, the lack of standardized reproducible diagnostic criteria for CFS, and in 2003 an International CFS Study Group published recommendations concerning application of the case definition. The Group recommended the use of validated instruments to obtain standardized measures of the major symptom domains of the illness (functional impairment, fatigue, and the accompanying symptom complex). This article reports the first study implementing the International CFS Study Group’s recommendations. Two hundred twenty-seven people from the general population of Wichita were identified as having CFS, unexplained chronic fatigue that did not meet criteria for CFS (which we term ISF), or CFS or ISF accompanied by melancholic depression or as being non-fatigued controls. We measured functional impairment by means of the Medical Outcomes Survey Short Form-36 (SF-36); we used the Multidimensional fatigue Inventory ( MFI) to obtain quantifiable measures of fatigue; we used the CDC Symptom Inventory to document the occurrence, duration and severity of the symptom complex. The article reports specific criteria (SF-36, MFI, and Symptom Inventory scores) that can be used to diagnose CFS. Defining CFS in this clinically empirical manner will improve the precision of case ascertainment in research studies, it will provide a standard reproducible means of following the clinical course over time, and it will help to clarify the extent to which patients from different studies are similar (or dissimilar). This means of diagnosis can also be used in primary care settings and will give health care professionals a standard and reproducible method for diagnosing CFS.

Abstract

Background : The lack of standardized criteria for defining chronic fatigue syndrome ( CFS) has constrained research. The objective of this study was to apply the 1994 CFS criteria by standardized reproducible criteria.

Methods : This population-based case control study enrolled 227 adults identified from the population of Wichita with: (1) CFS (n=58); (2) non-fatigued controls matched to CFS on sex, race, age and body mass index (n=55); (3) persons with medically unexplained fatigue not CFS, which we term ISF (n=59); (4) CFS accompanied by melancholic depression (n=27); and (5) ISF plus melancholic depression (n=28). Participants were admitted to a hospital for two days and underwent medical history and physical examination, the Diagnostic Interview Schedule, and laboratory testing to identify medical and psychiatric conditions exclusionary for CFS. Illness classification at the time of the clinical study utilized two algorithms: (1) the same criteria as in the surveillance study; (2) a standardized clinically empirical algorithm based on quantitative assessment of the major domains of CFS (impairment, fatigue, and accompanying symptoms).

Results : One hundred and sixty-four participants had no exclusionary conditions at the time of this study. Clinically empirical classification identified 43 subjects as CFS, 57 as ISF, and 64 as not ill. There was minimal association between the empirical classification and classification by the surveillance criteria. Subjects empirically classified as CFS had significantly worse impairment (evaluated by the SF-36), more severe fatigue (documented by the multidimensional fatigue inventory), more frequent and severe accompanying symptoms than those with ISF, who in turn had significantly worse scores than the not ill; this was not true for classification by the surveillance algorithm.

Conclusions : The empirical definition includes all aspects of CFS specified in the 1994 case definition and identifies persons with CFS in a precise manner that can be readily reproduced by both investigators and clinicians.

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