Defining CFS: The Debate Goes On
In 2005, the Centers for Disease Control and Prevention (CDC) CFS research group published a paper describing an empirical approach to defining CFS. (The full text can be accessed at
http://www.biomedcentral.com/1741-7015/3/19.) This paper proposed that administering three questionnaires would provide standardized, reproducible criteria for defining CFS. The three questionnaires included the Short Form 36 (SF36), an instrument that assesses disability; the multidimensional fatigue inventory (MFI) for patients to report mental and physical fatigue levels; and the CDC symptom inventory, a checklist of 19 symptoms and symptom frequency experienced by patients.
Self-report responses to these three instruments from subjects participating in the two-day in-hospital Wichita Clinical study were analyzed and it was concluded that “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.” Up until a recent publication by Leonard A. Jason and colleagues, there has been no application or reproduction of this empirical approach. In a paper published in the Journal of Disability Policy Studies this month, Dr. Jason documents serious flaws in the empiric CFS case definition for CFS and describes why it should not be used for further research on CFS.
Dr. Jason and his team recruited 27 subjects with CFS and 37 subjects with major depressive disorder (MDD) to participate in this study. All participants completed the three questionnaires described above. The data were then analyzed using the scoring criteria established by the CDC in the 2005 article. All 27 subjects diagnosed with CFS were classified as CFS using the empiric definition; however,
38% of those subjects who had a diagnosis of MDD being misclassified as having CFS. This resulted in 52% more subjects being classified as CFS by the empiric criteria compared to traditional means of determining the diagnosis.
The authors of this study determined that the empiric approach to defining CFS was overly inclusive because of the way the instruments are scored, capturing people who have only emotional and mental unwellness, without the necessary physical disability that is prominent in CFS.
This empiric CFS definition was used by CDC to estimate CFS prevalence in a community-based study of Georgia. Application of this criteria resulted in a quadrupling of the previous CDC CFS prevalence estimate, from one million Americans to four million Americans.
This revision generated a great deal of concern from members of the medical and scientific community that these prevalence estimates were inaccurate and identified people with primary psychiatric disorders, rather than CFS. Many of the formal and informal comments submitted to CDC after its request for input on a draft strategic plan echoed these concerns. This new study by Jason and colleagues validates the many issues raised.
It does not appear that the CDC CFS empiric case definition has been or will be adopted by others studying CFS and this paper should give CDC sufficient reason to reexamine its own use of this empiric case definition. A brief survey of CDC’s own web site (
www.cdc.gov/cfs) finds inconsistent prevalence estimates, suggesting that CDC may be wavering on scientific support for the higher estimates it published in June 2007.
As stated in the conclusion of Jason’s paper, “…
the erroneous inclusion of people with primary psychiatric conditions in CFS samples will have detrimental consequences for the interpretation of epidemiologic, etiologic, and treatment efficacy findings for people with CFS.” With so much left to discover about the origins, treatment and prevention of CFS, conflict over the definition of the condition stalls progress.
Jason LA, Najar N, Porter N, Reh C. Evaluating the Centers for Disease Control’s empirical chronic fatigue syndrome case Definition. Journal of Disability Policy Studies, volume 20, pages 93-100, September 2009.
Note: Suzanne D. Vernon, one of 10 authors listed on the 2005 paper, is no longer employed by CDC. Like many other scientists and advocates, she has expressed concerns about the CDC’s continued application of the empiric criteria which have shown not to serve the original intended purpose of providing standardized, reproducible criteria for CFS.
