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Flaws in the 1994 Case Definition

The 1994 CDC definition, unfortunately, has proven to be partially flawed. First, the Criteria was originally intended as a research definition and for that reason excluded CFS cases that might have certain dual diagnoses, for instance CFS and obesity and CFS and bi-polar disorder.

The CFS definition, however, had come into wide use clinically—that is to diagnose patients in normal medical settings. Hence, a number of research exclusions would prevent patients, with additional diagnoses, from properly receiving a CFS diagnosis. To its credit the CDC has currently recognized this problem.

The CDC definition refers to a "mental status examination". In the past, many physicians have been unclear as to how, and by whom, such an examination should be performed. The CDC now suggests this exam can be performed by the patient's examining physician.

The 1994 Criteria, itself, does not with acceptable accuracy, clinically identify and distinguish the actual illness. (This has been shown in convincing research studies. See some references mentioned in the Canadian Guidelines booklet). For this reason, research results that use the 1994 definition may also be flawed, as some subjects who do not have the illness are invariably included.

The 1994 definition puts too much emphasis on the existence of a major symptom—fatigue—while not taking into sufficient account other major symptom complexes or the peculiar characteristics of the fatigue (which include post-exertional malaise mimicking that found in mitochondrial disease occurring the day after minor exertion).

The definition clouds the now research-validated difference between psychiatric illnesses and the multi-systemic, physiological, and coherent disease entity which is ME/CFS—an illness with common immune, endocrine, cardiovascular, and neurological dysfunction.

More and more research is also identifying the involvement of viruses and other potential microbes, as well as involvement of the RNase-L system in cells. The 1994 definition is diagnostically not sufficiently rigorous as it permits the misdiagnosis of individuals with psychiatric illness as having ME/CFS, and conversely, permits individuals who actually have ME/CFS to be misdiagnosed as having psychiatric illness.

Moreover, the name itself, Chronic Fatigue Syndrome, is inaccurate and not only distorts the medical nature of the illness but also badly serves a real understanding of the illness by patients, physicians and the general public. Many of the U.S. and international researchers most knowledgeable about the illness clearly recognize the deficiencies of the case definition and the 1994 diagnostic criteria.

In an attempt to overcome the harm created by the name Chronic Fatigue Syndrome, patients in the United States, beginning in the early 1990s, have termed the illness Chronic Fatigue Immune Dysfunction Syndrome (CFIDS), since immune abnormalities in patients have been demonstrated by many definitive research studies. In 2012, the patient community in the United States has been advocating to the federal agencies the use of the name Myalgic Encephalomyelitis.

For a more detailed analysis of the flaws in the 1994 CDC Definition, see Critique of the CDC Case Definitions and  Detailed explanation of the 1994 CFS Definition .