Woman with head down" Progress in the understanding of CFS/ME, its nature and management, has increased wonderfully over the past 10 years as more and more countries, researchers, and clinicians have become involved. There is much reason for hope."


— Alan Gurwitt, M.D.

Retired clinician

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What Is ME/CFS?

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is also known as the Chronic Fatigue Immune Dysfunction Syndrome (CFIDS). In February, 2015 the Institute of Medicine of the National Academy of Sciences released a report on the illness suggesting that the name be changed to Systemic Exertional Intolerance Disease (SEID). So far U.S. federal government agencies are still referring to the illness as ME/CFS or just Chronic Fatigue Syndrome (CFS), not SEID.

ME/CFS is a complex, serious, and debilitating illness which affects multiple systems of the body. People with ME/CFS experience profound exhaustion, post-exertional malaise, sleep disorder, autonomic dysfunction, neurological and flu-like symptoms, and cognitive problems such as difficulty thinking, processing, and remembering.

In 2014, in an updated version of a primer for clinicians (ME/CFS: A Primer for Clinical Practitioners —written by an international committee of physicians specializing in treating patients with the illness), the authors explain:

     "The key feature of the syndrome, post-exertional malaise, is a worsening of symptoms following minimal physical or mental activity which can persist for hours, days or even weeks and is not relieved by rest. The pathological loss of energy of ME/CFS is very different from the fatigue felt by healthy people following strenuous exercise or who are living under stress.

      "Chronic fatigue syndrome (CFS) is an inappropriate name for this serious illness. Fatigue is universal in healthy people who have undergone too much activity or who have had insufficient rest. Chronic fatigue is also a frequent symptom in numerous other illnesses. The name ignores other abnormalities found in the illness and trivializes the severity of the symptoms."

Duration and course of the illness

ME/CFS may last many months or years. Symptoms may vary in severity and may wax and wane. A 25-year follow-up of his patients by Dr. David Bell found that some of his patients recovered, but some of those who didn't became increasingly incapacitated. The 10+ Long-term CFS Study found that the predominant symptoms became more neurological in patients ill more than fifteen years. More recent studies have found similar results.

Research has shown that there is no "typical" course of the illness. Both of the studies above found this. However, a 2014 New York multi-site study of ME/CFS patients ill more than five years found that temporary remissions, sometimes lengthy, were common.

While there is no known cure, many of the symptoms can be treated. Some patients show improvement over time, while others may show little improvement or a worsening of symptoms. The best strategy is for a patient to accept the fact of the illness and to develop coping skills that will make the situation as tolerable as possible. It is also important not to entirely give up on life, while waiting for the illness to resolve. It might not. See the section Living with ME/CFS for coping suggestions and the section on Treatment.

Who gets ME/CFS?

ME/CFS affects men, women, and children of all ages, ethnic and socioeconomic groups.  A very carefully conducted government-funded study (Jason et al.; Archives of Internal Medicine, Oct 11, 1999) estimated that there are about 1 million cases of ME/CFS in the US, with a majority of them being women.

This study found a prevalence among adolescents and children to be about half that of adults. The study also found the prevalence in women (522 per 100,000) is vastly higher than that for HIV in women (125 per 100,000), lung cancer in women (63 per 100,000) and breast cancer in women (43 per 100,000).

The study suggested that a high percentage of cases remain undiagnosed as a result of some patients' lower economic and medically uninsured status.

A 2008 study by the Centers for Disease Control & Prevention (CDC) now estimates the prevalence to be almost two million cases in the US, with 80% of them undiagnosed. However that study used a revised version of the 1994 CDC case definition, and probably over-estimates the prevalence.