The Five Competing Definitions of Chronic Fatigue Syndrome

It's Enough to Make You Pull Your Hair Out!

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When you're learning about chronic fatigue syndrome (ME/CFS), you're bound to come across references to things like Fukuda, Oxford criteria and the empirical definition. If you don't know what those things mean, or their context, it can be really confusing.

You've probably seen that there's a lot of controversy surrounding those things. That's a complex matter that goes back decades. Entire books have been written about it.

However, just understanding a few key points can help you decipher the things you read and help you put information in context.

The Five Competing Definitions

The medical community has had such a difficult time understanding ME/CFS that five different definitions are currently in play. Different researchers use different definitions, different doctors use different diagnostic criteria based on those definitions, and crossing a nation's border can sometimes mean encountering a different definition and set of criteria than what you're used to.

The physiological camp: Researchers in this group consider ME/CFS a physiological illness involving complex biological abnormalities. They research topics such as infection, environmental toxins, other factors that cause physiological stress, or a combination thereof.

When they select study participants, they may use one of these three definitions:

  1. Fukuda
    In 1994, the CDC adopted criteria put forth by the International Chronic Fatigue Syndrome Study Group. The paper was authored by Keiji Fukuda. His name has become the standard way that many people refer to these criteria.
  1. Canadian Criteria
    Put forth in 2010, these criteria are regarded as a more stringent and specific definition than Fukuda. They require more physical symptoms (including post-exertional malaise) and exclude people with symptoms of mental illness;
  2. International Consensus Criteria
    This definition uses the name myalgic encephalomyelitis (ME), replaces "fatigue" with "post-exertional neuroimmune exhaustion" and requires several physiological symptoms beyond what Fukuda does.

    A 2015 Institute of Medicine report offered new diagnostic criteria for ME/CFS and suggested a name change to systemic exertion intolerance disease (SEID.) It remains to be seen what impact this will have on research. However, the words "systemic" and "disease" make clear the report's contention that this is a physiological illness.

    The psychological/behavioral camp: researchers in this group emphasize the treatment of mental, emotional, and social aspects of ME/CFS. Its critics often refer to this as a biopsychosocial approach.

    When these researchers select study participants, they generally choose from one of these three definitions: stop

    1. Fukuda (see #1 above)
    2. Oxford Criteria
      These 1991 criteria include chronic fatigue of unknown origin plus post-infection fatigue syndrome.
    3. CDC empirical definition
      In 2005, the then-head of the CDC's chronic fatigue syndrome research revised Fukuda.

    So What Does This Mean for Research?

    With five definitions in active use, we face some real problems when it comes to learning about this condition and how to treat it.

    It's fairly common for one medical study to contradict another; however, when it comes to ME/CFS, there's bound to be even more conflicting results. It becomes harder to look at multiple studies and come up with valid conclusions.

    ME/CFS is complicated no matter what definition you use. Research into it is dramatically underfunded when you compare it to other illnesses affecting similar numbers of people. All the different definitions serve to slow down progress and keep the waters muddy.

    So What Does This Mean for People with ME/CFS?

    For the people living with this illness, it could mean waiting years longer for effective treatments. (After all, we still don't have a single FDA-approved drug for ME/CFS.)

    It can also mean that your doctor is less able to help you because he or she can't point to a body of research with clear conclusions. The confusion of likely contributes to the lingering doubts some doctors have as to whether am ME/CFS is even a "real" condition.

    Currently, there's a lot of heated debate about treatment called cognitive behavioral therapy (CBT). The two camps disagree on its usefulness in ME/CFS, with the second camp viewing CBT as a first-line treatment. It doesn't take long to find patients online who say they've been denied other treatments based on this belief, even when CBT didn't help them.

    What Does the Future Hold?

    It appears as though the folks doing physiological research are using the name myalgic encephalomyelitis more often, either along with chronic fatigue syndrome or instead of it. If this trend continues, I suspect that we'll eventually end up with two different illnesses with different names. With SEID emerging, however, researchers certainly have some things to consider.

    In the meantime, it'll continue to be an uphill battle for researchers, doctors, and patients alike to make heads or tails of this condition. The good news is that we are, slowly, making progress in spite of it all.


    Carruthers BM, et al. Journal of internal medicine. 2011 Oct;270(4):327-38. Myalgic encephalomyelitis: International Consensus Criteria.

    Carruthers BM, et al. Journal of chronic fatigue syndrome. 2003 11 (1): 7-36. Myalgic encehpalomyelitis/chronic fatigue syndrome: clinical working case definition, diagnostic and treatment protocols.

    Carruthers, Bruce M. and Marjorie I. van de Sande. All rights reserved. "Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: A Clinical Case Definition and Guidelines for Medical Practitioners"

    Centers for Disease Control and Prevention. "Diagnosing CFS" Accessed December 2012.

    Fukuda K, et al. Annals of internal medicine. 1994 Dec 15;121(12):953-9. The chronic fatigue syndrome: a comprehensive approach to its definition and study. International Chronic Fatigue Syndrome Study Group.

    Reeves WC, et al. BMC medicine. 2005 Dec 15;3:19. Chronic fatigue syndrome-a clinically empirical approach to its definition and study.

    Sharpe MC, et al. Journal of the Royal Society of Medicine. 1991 Feb;84(2):118-21. A report--chronic fatigue syndrome: guidelines for research.

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