By Suzanne D. Vernon, PhD, SMCI Scientific Director
The Institute of Medicine (IOM) convened a committee with expertise and experience in ME/CFS as well as other relevant medical and research domain experts. The committee was specifically charged with: 1) conducting a study to identify the evidence for various clinical diagnostic criteria for ME/CFS using a process with input from stakeholders, including practicing clinicians and patients; and 2) developing evidence-based clinical diagnostic criteria for ME/CFS for use by clinicians, using a consensus-building methodology. The result was the recommendation of new, evidence-based diagnostic criteria to diagnose ME/CFS. The new diagnostic criteria include the following three cardinal symptoms of ME/CFS, which the IOM proposed be renamed Systemic Exertion Intolerance Disease (SEID):
- A substantial reduction in activity
More specifically: A substantial reduction or impairment in the ability to engage in pre-illness levels of occupational, educational, social or personal activities that persists for more than six months and is accompanied by fatigue, which is often profound, is of new or definite onset—not lifelong—is not the result of ongoing excessive exertion, and is not substantially alleviated by rest;
- Post exertional malaise; and
- Unrefreshing sleep
AND one of these two:
- Cognitive impairment OR
- Orthostatic intolerance
Let’s start with the first recommended diagnostic criteria: “functional impairment that persists for more than six months along with fatigue.” Any attempt to study fatigue requires definition, measurement and interpretation. Yet for more than a century fatigue has defied definition and hence, effective measurement and interpretation. This is likely because fatigue is a subjective feeling or personal state. In fact, the International Classification of Diseases (ICD) classifies fatigue as a general, self-described symptom.
Fatigue is likely to be identified as a problematic symptom only when the individual is unable to obtain complete recovery through the normal processes of rest and sleep. In a 1940 address to the Omaha Midwest Clinical Society, which was published in the journal Psychosomatic Medicine, Wendell Muncie, M.D., of Johns Hopkins University explained that chronic fatigue was singly or in combination related to post-infectious states and endocrine-metabolic states.
Attempts at physiologic measures of fatigue have been inconclusive, and no specific measures have as yet been identified. Perhaps the only variable unique to fatigue is time. As C. Cameron wrote in a 1973 volume of Ergonomics: “Severity of fatigue is most effectively measured by the time required for the body to recover to homeostasis between exposures to the circumstances suspected of producing fatigue.”
This description puts severe fatigue in a context of time and homeostasis, or the ability of our body to monitor and regulate function. The IOM recommended that fatigue should be diagnosed using both time and impact on function:
“Conclusion: There is sufficient evidence that fatigue in ME/CFS is profound, not the result of ongoing excessive exertion and not substantially alleviated by rest. This fatigue results in substantial reduction or impairment in the ability to engage in pre-illness levels of occupational, educational, social or personal activities and persists for more than six months.”
To illustrate the impact of fatigue on function in ME/CFS, the IOM committee compared vitality across a number of diseases. Vitality is one of the scales on the SF36, a standardized assessment instrument that assesses energy and fatigue by asking for responses to four questions: 1. “How much of the time during the past four weeks did you have a lot of energy?;” 2. “… have you felt full of life?;” “… did you feel worn out?;” and 4. “… did you feel tired?” The committee’s comparison clearly illustrated the profound effects of ME/CFS on vitality; the table below shows some of the vitality scores for healthy people, a few diseases and ME/CFS/SEID.
|Congestive heart failure||
|Chronic hepatitis C patients||
Other research using the SF36 has shown that physical activity and social functioning are also impacted in ME/CFS. While the IOM noted the extensive use of the SF36 in research, it did not recommend it as a tool for doctors to use because it is complicated to score. However it seems reasonable that an app could be developed for use in a doctor’s office; in fact, a SF36 app already exists in the iTunes App Store, though it is not in English.
The stark differences in vitality scores between ME/CFS and a number of other diseases that are readily diagnosed and taken seriously indicates the importance of fatigue as one of the four criteria to diagnosis ME/CFS.
We will address the remaining criteria in subsequent blog posts, providing additional context and implications around them. The final post in this series will discuss how the scientific community can use these clinical diagnostic criteria to advance ME/CFS research.
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