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Defining an Illness: A Look at the Text and Philosophies of the 1994 Revised Case Definition for Chronic Fatigue Syndrome

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By Craig Maupin at

[Editor’s note: This is part three of the series “A Shaky Foundation”]

Early in the text of the 1994 CDC revised case definition, it becomes apparent the authors hoped to broaden what can be researched under the name of Chronic Fatigue Syndrome (CFS). The authors call for an integrated approach to the evaluation, classification, and study of persons with this condition and other fatiguing illnesses. Then, throughout the text of the case definition, they seek to lay a framework and some justification to get these “fatiguing illnesses” into the CFS research funding structure.

The authors of the case definition often refer to CFS as a fatiguing illness or as one of many fatiguing illnesses. There is more than one emerging illness for which the symptoms chronic fatigue may play a role. Therefore, many have assumed that many CFS researchers have branched out into funding research for unrelated fatiguing illnesses. The case definition seems to support this view.

Many estimates of the prevalence of CFS before 1994, when the revised CDC case definition was penned, seem to portray CFS as rare. At that time 250,000 was the ballpark figure for sufferers of CFS in the U.S. Now, just 10 years after the introduction of the 1994 CDC case definition, the estimates of CFS are suddenly pushing over 1 million. Did the illness change this drastically in 10 years? Did the illness spread? Probably not. It is logical to assume the broadening that was accomplished by the authors of the 1994 case definition may have actually played a larger role in the revised epidemiological numbers.

How CFS was Broadened: Downplaying the Hallmark Symptoms of CFS

The first way the authors of the case definition broadened the illness was to modify the way the hallmark symptom of CFS, fatigue, was defined. The 1988 Working Case Definition defined the hallmark fatigue of CFS more clearly. Terms such as “sudden onset,” and “debilitating” are descriptive, and the fatigue was also required to limit a person to 50% of their pre-illness capacity. Symptoms that were more variable among patients, such as muscle pain and neurological symptoms, were defined as minor symptoms.

Activity/exertion response – In CFS, the hallmark type of fatigue experienced is very distinct. First, it is closely related to exertion response. People with CFS typically have an exacerbation of symptoms 24-72 hours after exertion. CFS sufferers typically describe paying a price for the activities they wish to participate in. Unlike the typical fatigue experienced by healthy people, sleep or rest cannot alleviate it. Those with CFIDS also describe this fatigue as flu-like. This very distinct type of fatigue is the most telling symptom of CFS.

However, according to the 1994 CDC CFS case definition, a diagnosis of CFS can be made in patients without this hallmark symptom should a researcher choose to do so. Researchers may simply choose from a set of symptoms which fits their whims and interests. This approach to defining CFS for research purposes greatly broadened the illness, allowing researchers unlimited freedom to research a broad range of interests, under the new chronic fatigue syndrome label. One researcher may choose to select patients with myalgia as their main symptom, another might choose fatigue, and yet another might choose sleep disorder. It simply doesn’t matter.

Mixing in other distinct fatiguing illnesses with CFS liberally…

The second tool used to broaden the illness was to encourage researchers to include other fatiguing illnesses in their research samples. Repeatedly, the authors of the 1994 case definition called for an integrated approach to both the research and diagnosis of CFS. By the end of the revised definition, the authors had urged researchers to mix fibromyalgia, MCS (multiple chemical sensitivities), depression, and anxiety disorders freely into their patient samples.

Conversely, the earlier 1988 case definition did not urge researchers to include other fatiguing conditions in their research samples. The 1994 CDC case definition broke from this idea, encouraging researchers to practice integration. Today, much fibromyalgia research and stress disorder research is funded under a broad CFS umbrella, instead of building a distinct research structure for each illness. For some of the participants in drafting of the case definition, as well as critics of the earlier case definition, this may have been the end goal.

The authors could have decided to require CFS researchers to quantify their research samples for the presence of each of the above illnesses. While this would have still led to conflicting studies and a lot of confusion, it would have at least given researchers a way to interpret why their results may differ from their colleagues. But instead, they decided to allow researchers to mix these fatiguing illnesses without these standards. Mixing distinct illnesses in research samples is neither reliable nor justifiable under any circumstances, and it has made it impossible to effectively analyze or interpret CFS research.

Failing to Meaningfully Subgroup or Classify Patients

Contradictions in the 1994 case definition abound. In an earlier passage, the authors cite sloppiness in research standards as an unresolved dilemma. Subsequently, the authors promise that their new case definition would implement a strategy for subdividing the chronic fatigue syndrome and other unexplained cases of chronic fatigue into subgroups. This sounds like a courageous step in a positive direction. However, later the authors reveal that the only subgroup they intend to differentiate from CFS is idiopathic chronic fatigue/general unexplained fatigue.

Is idiopathic thirst a subgroup of diabetes? Is idiopathic pain a subgroup of arthritis? Of course not! Just as with these illnesses, it would appear that making idiopathic fatigue a subgroup of CFS would be unnecessary. Unexplained chronic fatigue is not a subgroup of CFS. True subgroups are used to classify different groups of patients by distinct symptoms. Contrary to their claims, the authors of the case definition chose not to meaningfully subgroup patients.

The harsh reality is that the text of the case definition veers in a direction vastly counter to true subgrouping and classification. Instead, the new case definition urged researchers to integrate and combine a vast number of fatiguing illnesses into their research samples and lower clinical distinctions. The complexities of the chronic fatigue syndrome make a comprehensive and integrated approach to the study of the chronic fatigue syndrome and similar illnesses desirable. The authors go on to encourage physicians and researchers to integrate into CFS research samples. Any condition defined primarily by symptoms that cannot be confirmed by diagnostic laboratory tests, including fibromyalgia, anxiety disorders, somatoform disorders, nonpsychotic or nonmelancholic depression, neurasthenia, and multiple chemical sensitivity disorder.

It doesn’t take an advanced scientific pedigree to realize that what the authors were crafting was a recipe for confusion and conflicting results. It also doesn’t take a rocket scientist to come to the conclusion that this is not subgrouping. Failure to classify patients by distinct symptoms has led to a severe loss of respect for the CFS research community.

Adding psychiatric patients to the CFS community – Using the Case Definition to Steer Patients with Pre-existing psychiatric disorders into CFS.

Throughout the revised case definition, the authors not only urge a breaking down of the distinctions between CFS and fibromyalgia, MCS, and other fatigue-producing diseases, but they urge researchers to break down distinction between CFS and psychiatric disorders as well. Remarkably, they assert that mixing research samples of psychiatric disorders into CFS research samples would be certain to lead to a “clarification” of the illness. They state that the exclusion of persons with these conditions would substantially hinder efforts to clarify the role that psychiatric disorders have in fatiguing illnesses.

But in respect to CFS and real world scientific methods, this assertion raises more questions than answers. At the very least, it could be stated that the authors gave very little concrete support for their claims.

This passage is strongly representative of the approach and philosophy of Michael Sharpe, a psychiatrist who played a strong role in the drafting of the CDC’s revised case definition. Sharpe has been a strong proponent of a psychiatric and behavioral model for CFS. Other participants, such as Stephen Strauss, have expressed admiration for this behavioral model for CFS, as well as his integrative loose approach to defining CFS.

In 1991, Sharpe helped author the broadest of definitions for CFS, the Oxford Criteria. The Oxford Criteria, used by a politically vocal minority of CFS researchers, simply requires prolonged fatigue for a CFS diagnosis. Studies have shown that the Oxford Criteria catches a broad variety of psychiatric illnesses, and it is very popular with many researchers who favor a behavioral or psychiatric view of any emerging or poorly understood illness.

The creation and use of looser, less rigorous standards by proponents of a behavioral model for CFS, has raised legitimate allegations that case definitions for CFS are often more a political and funding exercise, rather than scientifically solid. Did some of the participants in the drafting of the case definition see the definition as more of a means to personal ambition than for true scientific inquiry? The redrawing of case definitions for CFS to broader, looser standards is a common practice among those who champion a psychiatric model for CFS. Speculation has run rampant that this may have been a leading motivation for several of the participants of the 1994 revised case definition as well.

One CFS researcher critical to the 1994 case definition explains, inappropriate use of the case definition leads to the inclusion of individuals who only have a psychiatric condition, and will present difficulties in interpreting the results of epidemiological and treatment studies.

The Poor Results Should Have been Predictable…

In the years to follow the creation of the revised CFS case definition, the conflicting results of the CDC s freewheeling approach should have been anticipated. There also should have been more criticism of the definition’s assumptions from the scientific community at large. But the truth is that the CFS research community is generally insulated from the at-large scientific community, and it is also very politically driven.

Due to these reasons, CFS research as a whole has had great difficulty in attracting talented researchers. A strong case could be made that more exact standards and scientifically rigorous methods could have a direct impact in attracting more qualified, meticulous researchers to CFS research. But in order for new more rigorous standards to become a part of the CFS research community, a new set of researchers willing to challenge the currently shaky ideological foundation espoused by many current CFS researchers will need to step forward.

While some researchers have had the courage to speak out, most published CFS researchers ignore voluntary standards, and seem to show little enthusiasm for anything but a shaky, clever defense of the current system. Therefore, it would be hard to assume they would be in favor of implementing any kind of research standards that would make CFS research interpretable and reliable. A new breed of researchers will need to take the reins before true reform of CFS research is achievable.

© CFIDS Report. Reprinted with permission.

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