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CFS Definitions

 "Criterion variance is likely to occur when explicit criteria do not exist for diagnostic categories.  For example the US case definition of CFS treats two central symptoms, post-exertional malaise and cognitive impairment, as optional rather than required criteria."
-Jason, Taylor, Song, Kennedy, Johnson-

"Do not for one minute believe that CFS is simply another name for Myalgic Encephalomyelitis (M.E.).  It is not.  Though CFS is based upon a typical M.E. epidemic, in my opinion it has always been a confused and distorted view of reality.
The invention of Chronic Fatigue Syndrome has to be one of the most curious cases of inventive American imperialism that one could imagine."
-Dr. Byron Hyde -

The first CFS definition (Holmes, CDC USA, 1988) was invented during an outbreak of what can only be described as distinct ME in Nevada at Lake Tahoe in the mid-1980s. (See note on Dr. Hyde's page.) Various sources will say that the the renaming of ME was either deliberate for political and insurance purposes, or just a bungle of bureaucracy, or perhaps both.  Either way, it ignited an ongoing controversy that has lasted to the present, bogging down research and delaying discovery of effective treatments while patients linger - debilitated, declining and dying fairly young (see Mortality) after years of chronic illness.  Two Australian CFS definitions appeared shortly after the US definition (Lloyd et al, 1988, 1990), and another came out of Great Britain (Oxford, 1991).  (See sidebar for links to summaries of these and other definitions.)

All of these definitions focused on fatigue, and did/do not exclude psychiatric illness as a cause of the fatigue.

The Centers for Disease Control revised the 1988 CFS definition in 1994 (Fukuda, 1994).  It is currently in use for research and clinical diagnosis in the US and most countries abroad.  That these definitions were prepared by government bureaucrats, rather than by physicians who had collectively seen, studied and treated thousands of patients with the illness, is testimony to their validity (or lack thereof). Dr. Nancy Klimas from the University of Miami School of Medicine and long-time researcher into immune abnormalities in ME and CFS, commented on the revised 1994 definition: "...the resulting guidelines are rife with ambiguity.  Symptoms are counted either as present or absent, without regard to severity or frequency."  (See below 4 research articles that study the flaws in this definition.)

A major complaint researchers and patients have with this definition is that it is broad and unspecific, and focuses on a single symptom--fatigue.  There are many diseases that can cause debilitating fatigue, including psychological illnesses, that may not be covered by the CDC's list of exclusionary diseases in this definition.  Thus, a patient diagnosed with CFS may have some other underlying condition that doctors failed to detect.  Dr. Byron Hyde makes this very clear in The Complexities of Diagnosis, while Dr. E.G. Dowsett states in A Rose By Any Other Name that the CDC definitions "elevated tonsillitis, glandular enlargement and fatigue to unreal importance while overlooking the characteristic encephalitic features of the genuine disease."

From the CDC website on chronic fatigue syndrome:

Chronic fatigue syndrome, or CFS, is a debilitating and complex disorder characterized by profound fatigue that is not improved by bed rest and that may be worsened by physical or mental activity. Persons with CFS most often function at a substantially lower level of activity than they were capable of before the onset of illness. In addition to these key defining characteristics, patients report various nonspecific symptoms, including weakness, muscle pain, impaired memory and/or mental concentration, insomnia, and post-exertional fatigue lasting more than 24 hours. In some cases, CFS can persist for years. The cause or causes of CFS have not been identified and no specific diagnostic tests are available. Moreover, since many illnesses have incapacitating fatigue as a symptom, care must be taken to exclude other known and often treatable conditions before a diagnosis of CFS is made.

Definition of CFS
A great deal of debate has surrounded the issue of how best to define CFS. In an effort to resolve these issues, an international panel of CFS research experts convened in 1994 to draft a definition of CFS that would be useful both to researchers studying the illness and to clinicians diagnosing it. In essence, in order to receive a diagnosis of chronic fatigue syndrome, a patient must satisfy two criteria:

  • Have severe chronic fatigue of six months or longer duration with other known medical conditions excluded by clinical diagnosis; and

  • Concurrently have 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.

The symptoms must have persisted or recurred during six or more consecutive months of illness and must not have predated the fatigue.

[Click here for the complete CDC [Fukuda, 1994] CFS Case Definition.]

Four studies from two separate research groups demonstrate the need to revise or replace this definition:

Chronic fatigue syndrome: The need for subtypes.  Jason, L.A., Corradi, K., Torres-Harding, S., Taylor, R.R., & King, C. (2005).  Neuropsychology Review, 15, 29-58. "The current U.S. case definition for CFS (Fukuda et al., 1994) is characterized by vaguely worded criteria that lack operations definition and guidelines to assist health care professional in their interpretation and application of the diagnostic too. (Jason et al., 1999d).  The Canadian case definition [includes] these critical symptoms and use of such types of case definitions might aid in the selection of more homogeneous samples. Based on the research reviewed in this section, we would encourage researchers to compare and contrast categories of patients meeting the Canadian Case definition and the Fukuda et al. (1994) criteria.  In addition, the provision of standardized measures for assessment and scoring guidelines should reduce clinicians’ difficulty with the criteria and their need to modify the criteria in clinical practice. In effect, the use of standardized measures should reduce criterion variance and improve diagnostic reliability (King and Jason, 2004)."
(Abstract and summary only)

Comparing the Fukuda et al. criteria and the Canadian case definition for chronic fatigue syndrome.  Jason, L.A., Torres-Harding, S.R., Jurgens, A., & Helgerson, J. (2004).  Journal of Chronic Fatigue Syndrome, 12, 37-52.  "...those individuals in this study meeting the Canadian criteria appear to have more symptoms, more physical functional impairment, and less psychopathology than those in the CF-psychiatric group.  In addition, the Canadian criteria identifies patients with more fatigue/weakness, neurological and neuropsychiatric symptoms than the Fukuda CFS criteria does."

The specificity of the CDC-1994 criteria for chronic fatigue syndrome: comparison of health status in three groups of patients who fulfil the criteria. (Abstract) Kennedy G, Abbot NC, Spence V, Underwood C, Belch JJF Institution: Vascular Diseases Research Unit, Department of Medicine, University of Dundee.  "Aim: The Centers for Disease Control (CDC)-1994 definition of chronic fatigue syndrome (CFS) is very broad, and there have been suggestions that it lacks specificity. Conclusions: Differences in simple, easily performed clinical outcome measurements can be observed between groups of patients, all of whom fulfill the CDC-1994 criteria for CFS. It is likely that their response to treatment may also vary. The specificity of the CFS case definition should be improved to define more homogeneous groups of patients for the purposes of treatment and research."

Politics, science, and the emergence of a new disease: The case of Chronic Fatigue Syndrome. (Abstract) Jason, L.A., Richman, J.A., Friedberg, F., Wagner, L., Taylor, R., & Jordan, K.M. (1997).  American Psychologist, 52, 973-983.  "Many physicians minimized the seriousness of this disorder and also interpreted the syndrome as being equivalent to a psychiatric disorder. These attitudes had negative consequences for the treatment of CFS."



Definitions Overview
ICC - Consensus Criteria
Canadian Consensus
Dr. Byron Hyde
Historic ME
Dr. A. Melvin Ramsay
Dr. E.G. Dowsett
Prof. Malcolm Hooper
ME/cfs Australia
Pediatric ME & cfs

Problems with the New CDC CFS Prevalence Estimates
Leonard Jason, Ph.D., DePaul University

Sign the Petition:
CDC CFS research should not involve the Reeves 2005 empirical definition


ME Research UK comments on the 1994 CDC CFS Definition:

So, should anything be done about the CDC-1994 case definition?  Some — predominantly mental health professions — are (probably) content to maintain the status quo, and view "CFS" as one of a number of different syndrome-lagoons which overlap to give a larger, vaster sea of "medically unexplained symptoms/illnesses" best treated with psychological if not frank psychiatric interventions.

Another wide-ranging group of researchers prefer a more radical option, such as the specific extraction of research-based subsets of patients (recommended by the authors of at least 6 scientific papers in recent months) or the shattering of the term "CFS" and the creation of other definitions based on specific symptom clusters or signs. For example, a recent systematic
clinical working case definition (evidence-based on data from over 2,500 patients, including diagnostic protocols and treatment protocols, has been published: this encourages a diagnosis based on characteristic patterns of symptom clusters, which reflect specific areas of pathogenesis.

In addition, efforts are underway to compare older definitions, such as that for myalgic encephalomyelitis, with CDC-1994 CFS to explore the usefulness of these.
Interestingly, the Kennedy et al. results showing a significant degree of muscle weakness and abnormalities at reflex testing in all three groups point to the fact that subgrouping patients on the basis of objective clinical signs may be practical and informative, as recommended in some of the older literature on the subject of myalgic encephalomyelitis.

(Read full text, article abstract and references here.)

See a summaries and comparisons of CFS and ME definitions
here and here.

"The diagnostic mess that is ME/CFS is illustrated by our own research in 2004 which found that distinct differences could be found between three groups of patients all of whom fulfilled criteria for the 1994 CDC Fukuda definition of CFS."
-Dr. Vance Spence-

A Response and Appreciation of the Gibson Inquiry Report
-Prof. Malcolm Hooper-
December 2006
"The Canadian Guidelines and Criteria also address the vexed question of differential diagnosis that is key to treatment, care and benefits.  A note of caution concerns the general comments about the work in the USA.  Some of this is high quality and ground breaking but there is also a powerful lobby that supports the biopsychosocial  / somatisation views so wholeheartedly and misguidedly embraced by the UK medical fraternity and insurance industries.  Drs. Strauss and Reeves in the States endorse this approach and advocate both CBT and GET.  The CDC toolkit cannot be recommended whilst the CDC (Fukuda) research criteria for ME/CFS are now known to be flawed, Kennedy, Spence et al 2004, Jason et al, 2005, and need to be replaced by more specific and focussed criteria such as the Canadian ones."

"CFS is little more than a collection of symptoms at the present time, and it remains highly likely that many patients' symptoms are actually caused by lymphomas, multiple sclerosis, or any of multiple other chronic diseases that may not be diagnosed in the initial evaluation."  Gary Holmes (author of the original "CFS" definition - Holmes, 1988) in Osler's Web.

Online Medical Dictionary


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