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

Article Index

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.

How is ME/CFS diagnosed?

ME/CFS often resembles other illnesses, including Lyme disease, multiple sclerosis, mononucleosis, primary depression, mitochondrial disease and lupus.

In medicine, a "syndrome" is a set of signs and symptoms that occur together in a medical condition. For instance, AIDS is Acquired Immunodeficiency Syndrome, and until infection by the HIV virus was discovered to be the cause, diagnosis of AIDS was made solely by a collection of signs and symptoms. (In medicine, a "sign" is something that can be objectively measured by a physician and a "symptom" is something subjective experienced by a patient, such as severity of pain.)

In the 1980s, a number of U.S. physicians noticed what seemed to be an emerging syndrome. The Centers for Disease Control and Prevention (CDC) were called in to investigate an outbreak in the Lake Tahoe, Nevada area. Later the CDC convened a committee to come up with a research definition of the syndrome using signs and symptoms. This is now known as the 1988 CDC definition and the illness was named the Chronic Fatigue Syndrome (CFS).

In 1994, the CDC came up with a new research case definition, which loosened the requirements for diagnosis with ME/CFS. This is known as the 1994 CDC definition. Both definitions were intended to be used by researchers, to make sure their research subjects all had the same illness.

Unfortunately, it has been shown that the 1994 requirements were loosened too much compared to the 1988 definition, and people with other illnesses (including depression) were being mistakenly diagnosed as having ME/CFS. This has created major problems for the ME/CFS research results of the last 20 years, since in studies some of the subjects didn't have ME/CFS, but were mixed in with those who did. (See " Critique of the 1994 CDC definition " and the discussion "Are the illnesses described by the 1988 and 1994 CDC definitions the same?") 

Later a Canadian, Dr. Carruthers, led an international team of clinicians to come up with a definition of ME/CFS to be used by physicians who regularly see patients. This was published in 2003 under the auspices of the Canadian Ministry of Health.

This 2003 Canadian definition is what the physician authors of the Primer suggest be used for diagnosing ME/CFS. Unfortunately, the definition is complex. We will give a summary below. For more detail, see the article 2003 Canadian definition and pp. 43-44 of the ME/CFS: A Primer for Clinical Practitioners. All quotations below are from the original medical paper.1


2003 Canadian case definition of ME/CFS

The definition first requires that other illnesses which could explain a patient's symptoms be ruled out. 

To have ME/CFS, a patient must meet all four of these criteria:

  • "the criteria for fatigue, post-exertional malaise and/or fatigue, sleep dysfunction, and pain" explained below
  • "have two or more neurological/cognitive manifestations"
  • "one or more symptoms from the categories of autonomic, neuroendocrine and immune manifestations"
  • "the illness persists for at least six months usually having a distinct onset, although it may be gradual." A "preliminary diagnosis may be  possible earlier."

Thus, to be diagnosed the person must qualify under each and all of the following symptom categories:

  • "Fatigue: The patient must have a significant degree of new onset, unexplained, persistent, or recurrent physical and mental fatigue that reduces activity level. Three months is appropriate for children."
  • "Post-exertional malaise...There is an inappropriate loss of physical and mental stamina, rapid muscular and cognitive fatigability, post-exertional malaise...and/or pain and a tendency of other associated symptoms within the patient's cluster of symptoms to worsen. There is a pathologically slow recovery period—usually 24 hours or longer."
  • Sleep dysfunction: There is non-restorative sleep or decline in sleep quantity or dysregulation of normal sleep rhythms.
  • Pain. "There is a significant degree of myalgia." The word means muscle pain, and is often the type of deep muscle pain experienced during the flu. "Pain can be experienced in the muscles/joints, and is often widespread and migratory in nature." There are often headaches of a "new type, pattern or severity."
  • "Neurological/Cognitive Manifestations"—To qualify in this category two or more of the listed symptoms must be present. Please see the specific list of symptoms in the actual document. They are grouped into:

    a) cognitive deficits including problems with memory, information processing, difficulties with thinking, and perceptual disturbances

    b) more classical neurological symptoms, including difficulty walking and muscle weakness; sensory hypersensitivity, including lower threshold for emotional overload.

  • "Autonomic, Neuroendocrine and Immune Manifestations"—To qualify under this category the patient must have at least one symptom from two of the following three subcategories. Often a patient will have multiple symptoms:

    a) "Autonomic Manifestations: orthostatic intolerance, neurally-mediated hypotension; postural orthostatic tachycardia; light-headedness; extreme pallor; nausea and irritable bowel syndrome; urinary frequency and bladder dysfunction; difficulty breathing upon exertion; palpitations with or without cardiac arrhythmias."

    b) "Neuroendocrine Manifestations: loss of thermostatic stability—subnormal body temperature...sweating episodes, recurrent feelings of feverishness and cold extremities; intolerance of heat and cold, marked weight change—anorexia or abnormal appetite; loss of adaptability and worsening symptoms with stress."

    c) "Immune Manifestations: tender lymph nodes, recurrent sore throats, recurrent flu-like symptoms, general malaise, new sensitivities to food, medications and or chemicals."



1. Carruthers et al. "Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Clinical Working Definition, Diagnostic and Treatment Protocols," Journal of Chronic Fatigue Syndrome 11, No. 1 (2003): 18-126.

Other Important ME/CFS Symptoms

Onset of the illness is often sudden (a few days to a few weeks.) Common symptoms (where patients were diagnosed with the 1988 or 1994 CDC case definitions) with their incidences are on the following list compiled from information provided by famous ME/CFS clinicians.

Most Common Symptoms of ME/CFS

  • Exhaustion, made worse by physical exercise (100%)
  • Low-grade fever in early stages (60-95%)
  • Recurrent flu-like illness (75%)
  • Frequent pharyngitis (sore throats) (50-75%)
  • Joint and muscle pain (65%)
  • Severe muscle weakness (40-70%)
  • Stiffness (50-60%)
  • Post-exertional fatigue & flu-like symptoms (50-60%)
  • Multiple sensitivities to medicines, foods, and chemicals (40-60%)
  • Severe nasal & other allergies (often with worsening of previous mild allergies) (40-60%)
  • Frequently recurring, difficult to treat respiratory infections (40-60%)
  • Dyspnea (labored breathing or hunger for air) on exertion
  • Painful lymph nodes (especially on neck and under arms) (30-40%)

Neurological Symptoms

  • Sleep disorders & unrefreshing sleep (50-90%)
  • Headaches (35-85%)
  • Visual blurring (50-60%)
  • Intolerance of bright lights
  • Parasthesias (numbness or tingling feelings) (30-50%)
  • Dizziness/ Lightheadedness (30-50%)
  • Ringing in the ears
  • Impaired cognition (50-85%)
    • Attentional difficulties
    • Calculation difficulties
    • Memory disturbance
    • Spatial disorientation
    • Saying the wrong word

    Other Symptoms

  • Worsening of premenstrual symptoms (70% of women)
  • Nocturia (excessive urination during the night) (50-60%)
  • Tachycardia (abnormal rapid heart action) (40-50%)
  • Chest pain (25-40%)
  • Cough (30-40%)
  • Weight gain (50-70%)
  • Nausea, especially in earlier stages (50-60%)
  • Diarrhea, intestinal gas or irritable bowel (50%)
  • Intolerance of alcohol
  • Night sweats (30-50%)
  • Dry eyes (30-40%)
  • Dry mouth (30-40%)
  • Rash (30-40%)
  • Frequent canker sores (30-40%)
  • Herpes simplex or shingles (20%)
  • Symptoms worsened by extremes in temperature


(Statistics compiled from data by: Paul Cheney MD, Anthony Komaroff MD, Charles Lapp MD, Daniel Peterson MD)

What Causes ME/CFS?

The cause of ME/CFS is not yet known, but current research shows strong evidence of immune, neuroendocrine, and circulatory system dysfunction. Research indicates that some parts of the immune system may be in an overactive state, while other parts of the system may be in an underactive state. There is convincing evidence that viruses or persistent viral fragments are associated with ME/CFS in many cases.

The authors of ME/CFS: A Primer for Clinical Practitioners (p. 43) have this to say about causality:

       "ME/CFS usually occurs as sporadic (isolated) cases, but clusters of cases have occurred worldwide. Some outbreaks have affected large
numbers of individuals in a particular community, hospital, or school. In sporadic cases, 20% of patients have another family member with the illness. These facts suggest that both genetic and environmental factors may contribute to the illness.

"ME/CFS frequently starts with acute, 'flu-like' symptoms and immune system changes found in ME/CFS are similar to immune system changes
found in some viral infections. A number of infectious agents have been found more frequently in patients with ME/CFS than in the general population,
but no infectious agent has been proven to be the cause.

"To avoid any possible contamination of the blood supply, patients with ME/CFS should refrain from donating blood.

"Occasionally, ME/CFS has been triggered by environmental toxins, the receipt of an immunizing injection, or surviving a
major trauma.

"Although depression and anxiety may occur secondary to the illness, research studies have shown that ME/CFS and major depressive disorder
can be distinguished by behavioral, immunological and hormonal testing.

"The Centers for Disease Control and Prevention (CDC) recognizes CFS as an organic syndrome, not a psychiatric disorder." 

How is ME/CFS treated?

Since there is no known cause or cure, treatment is targeted to relieve specific symptoms, such as pain and sleep disorder. Experienced ME/CFS clinicians are treating patients with both conventional and alternative approaches. Experimental treatments are being evaluated in clinical trials. Patients need to assess their treatment options carefully for safety and effectiveness. (See our detailed Treatment section.)

Because some patients can show lower tolerance or hypersensitivity to medications, treatment should be started at low doses with gradual increases as appropriate. Since anesthesia can also trigger hypersensitive reactions, caution must be exercised when an ME/CFS patient undergoes a procedure using anesthesia. (See the suggestions of Dr. Charles Lapp concerning the use of anesthesia.)

Important lifestyle changes include: increased rest, decreased and carefully paced activity ("living in your energy envelope"), exercise only as tolerated, stress control, balanced nutrition, improved sleep, and identifying effective coping strategies.

Patient and family support groups, as well as counseling, can be very helpful. It is vital to find a physician who understands ME/CFS, and is willing to develop an individualized treatment program.

What about kids?

Children develop ME/CFS, but they are often misdiagnosed. An accurate pediatric definition of ME/CFS has only been in existence since 2006.

Children tend to experience symptoms of short-term memory and concentration problems, dizziness, light-headedness, abdominal pain, rash, fever, and chills. They frequently experience profound fatigue as well, although they may have difficulty expressing their complaints or judging the severity of their condition.

Thus, some people may incorrectly perceive that the child is developing progressive learning and social difficulties rather than a physical illness. (Please see our Pediatric ME/CFS section for more information.)

More resources

Clinical Guides to Diagnosis and Treatment

Complementary & Mainstream Treatment Approaches

Conventional Medicine Treatment for ME/CFS

Critique of the 1994 CDC case definition

Dr. Anthony Komaroff, An Overview of Research on CFS, summary of lecture April 24, 2010

History of ME/CFS/CFIDS

Leading doctors explain ME/CFS in videos and text

ME/CFS: A Primer for Clinical Practitioners

ME/CFS Self-Care: The Basics

On the Morbid Fascination with Psychiatric Morbidity

The ME/CFS Initiation–A Primer for New Patients

The Physical Basis of CFS