Rare Infectious Disease News

Disease Profile

Myalgic encephalomyelitis/chronic fatigue syndrome

Prevalence estimates on Rare Medical Network websites are calculated based on data available from numerous sources, including US and European government statistics, the NIH, Orphanet, and published epidemiologic studies. Rare disease population data is recognized to be highly variable, and based on a wide variety of source data and methodologies, so the prevalence data on this site should be assumed to be estimated and cannot be considered to be absolutely correct.


US Estimated

Europe Estimated

Age of onset





Autosomal dominant A pathogenic variant in only one gene copy in each cell is sufficient to cause an autosomal dominant disease.


Autosomal recessive Pathogenic variants in both copies of each gene of the chromosome are needed to cause an autosomal recessive disease and observe the mutant phenotype.


dominant X-linked dominant inheritance, sometimes referred to as X-linked dominance, is a mode of genetic inheritance by which a dominant gene is carried on the X chromosome.


recessive Pathogenic variants in both copies of a gene on the X chromosome cause an X-linked recessive disorder.


Mitochondrial or multigenic Mitochondrial genetic disorders can be caused by changes (mutations) in either the mitochondrial DNA or nuclear DNA that lead to dysfunction of the mitochondria and inadequate production of energy.


Multigenic or multifactor Inheritance involving many factors, of which at least one is genetic but none is of overwhelming importance, as in the causation of a disease by multiple genetic and environmental factors.


Not applicable


Other names (AKA)

Systemic exertion intolerance disease; ME/CFS; Chronic fatigue syndrome/ myalgic encephalomyelitis


Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is an umbrella term that includes both myalgic encephalomyelitis (ME) and chronic fatigue syndrome (CFS). It is a serious, chronic and complex disease that affects many systems of the body and can profoundly impact daily activities. The main symptom is disabling fatigue that does not improve with rest and lasts at least 6 months.[1][2] Fatigue may get worse after activity, which is known as post-exertional malaise. Other signs and symptoms may include muscle pain, joint pain, concentration and memory problems, headaches, sleep problems, fever, sore throat, and/or tender lymph nodes.[3][1] ME/CFS generally occurs in young adults (20 to 40 years of age) and is twice as common in women.[1][4][2][5] 

The exact cause is not known, but symptoms may be triggered by an infection.[4][1] Diagnosis can be difficult as there are no specific laboratory tests and the symptoms are common to a number of different illnesses. There is no cure or effective treatment for this condition but there are several clinical trials.[3][6][5] 

While the term ME/CFS is widely used, there is still a debate in the medical literature about the relationship between myalgic encephalomyelitis and chronic fatigue syndrome and there is no universally accepted definition.[7] The term “systemic exertion intolerance disease” has been proposed as new term for both diseases.[6]


The cause of myalgic encephalomyelitis/chronic fatigue syndrome is not known. Some researchers have proposed that this condition is caused by viral infections or by immunological, hormonal or psychiatric problems. However, none of these possible explanations are proven.[4][1] Some researchers believe that there may be a genetic predisposition for this condition and stress-related events act as triggers.[4][6]


The Committee on the Diagnostic Criteria for Myalgic Encephalomyelitis/Chronic Fatigue Syndrome, The Board of Select Populations, and the Institute of Medicine proposed diagnostic criteria which requires that the patient have the following three symptoms:[4]

  1. Chronic fatigue that interferes with daily activities and work, which is often profound, is of new or definite onset (not lifelong), is not the result of excessive exertion or other medical conditions, and is not greatly alleviated by rest.
  2.  Post-exertional malaise
  3.  Unrefreshing sleep. 

At least one of the two following symptoms is also required:

  • Cognitive impairment (impairment of short-term memory or concentration).
  • Orthostatic intolerance (Onset of symptoms when standing upright that are improved by lying back down).

Other symptoms include post exertion illness lasting more than 24 hours, muscle pain, pain in the joints, headaches, tender lymph nodes, and sore throat.

These symptoms should have persisted or recurred during 6 or more consecutive months of illness and they cannot have first appeared before the fatigue.

The diagnosis can only be made after 6 months because many other causes of similar fatigue do not last beyond 6 months. The patients should be asked questions about the frequency and severity of their symptoms. Questionnaires or clinical observations that may help the diagnosis should also be used, such as the Wood Mental Fatigue Inventory.

While there are no laboratory tests that can diagnose ME/CFS directly, the following tests, together with the symptoms, support the diagnosis (these tests are not routinely required, nor do negative results rule out the diagnosis):[6]

Sleep studies do not seem to help to the diagnosis of this disorder. Neurological or psychological testing is not required for diagnosis.

Other symptoms and testing that may support the diagnosis may include:[6] 

  • History of past infection from which patient never fully recovered with or without blood exams that show the presence of virus-specific immunoglobulin M (IgM), near the onset of illness.
  • History of having repeated infections with or without exams showing an abnormal immune function, such as decreased function of natural killer cells in those with severe disease.

Many patients have other disorders as well, some of which—including fibromyalgia, irritable bowel syndrome, metabolic syndrome, sleep disorders, and depression—may have symptoms that overlap with those of CFS. The diagnosis and treatment of these conditions is necessary when caring for patients.[6][4]


Treatment is mostly supportive and is focused on the specific symptoms present in each affected person.[8][4] Treating the symptoms might provide relief for some patients with ME/CFS but not others.

Medications, special diets, vitamin supplements, behavioral therapies, and exercise therapies have been evaluated as treatments for ME/CFS, but none have been proven effective and none is specifically recommended. No drugs have been FDA-approved for ME/CFS treatment.[8][9][10] Several clinical trials aiming to find effective treatments are currently ongoing.

Other disorders that may be present, such as sleep disorders, and depression should be treated when caring for patients.[6][4]

Management Guidelines

  • The National Guideline Clearinghouse (NGC) is a public resource for evidence-based clinical practice guidelines. The NGC was originally created by the Agency for Healthcare Research and Quality (AHRQ) in partnership with the American Medical Association and the American Association of Health Plans.


    Support and advocacy groups can help you connect with other patients and families, and they can provide valuable services. Many develop patient-centered information and are the driving force behind research for better treatments and possible cures. They can direct you to research, resources, and services. Many organizations also have experts who serve as medical advisors or provide lists of doctors/clinics. Visit the group’s website or contact them to learn about the services they offer. Inclusion on this list is not an endorsement by GARD.

    Organizations Supporting this Disease

      Learn more

      These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.

      Where to Start

      • The Mayo Foundation for Medical Education and Research also provides information about chronic fatigue syndrome. Click on the link above to view this information page.
      • You can obtain information on this topic from the Centers for Disease Control and Prevention (CDC). The CDC is recognized as the lead federal agency for developing and applying disease prevention and control, environmental health, and health promotion and education activities designed to improve the health of the people of the United States.
      • The Lab Tests Online Web site provides additional information on Myalgic encephalomyelitis/chronic fatigue syndrome.
      • MedlinePlus was designed by the National Library of Medicine to help you research your health questions, and it provides more information about this topic.
      • The Merck Manuals Online Medical Library provides information on this condition for patients and caregivers.
      • The National Organization for Rare Disorders (NORD) has a report for patients and families about this condition. NORD is a patient advocacy organization for individuals with rare diseases and the organizations that serve them.

        In-Depth Information

        • Medscape Reference provides information on this topic. You may need to register to view the medical textbook, but registration is free.
        • MeSH® (Medical Subject Headings) is a terminology tool used by the National Library of Medicine. Click on the link to view information on this topic.
        • Orphanet is a European reference portal for information on rare diseases and orphan drugs. Access to this database is free of charge.
        • PubMed is a searchable database of medical literature and lists journal articles that discuss Myalgic encephalomyelitis/chronic fatigue syndrome. Click on the link to view a sample search on this topic.


          1. Hatron PY. Chronic Fatigue Syndrome. Orphanet. April 2009; https://www.orpha.net/consor/cgi-bin/OC_Exp.php?lng=EN&Expert=1983.
          2. Myalgic encephalomyelitis/chronic fatigue syndrome. Centers for Disease Control and Prevention (CDC). January 17, 2020; https://www.cdc.gov/me-cfs/index.html.
          3. Chronic fatigue syndrome. MedlinePlus. May 19, 2015; https://www.nlm.nih.gov/medlineplus/chronicfatiguesyndrome.html.
          4. Gluckman SJ, Aronson MD & Park L. Clinical features and diagnosis of chronic fatigue syndrome (systemic exertion intolerance disease). UpToDate. October 11, 2018; https://www.uptodate.com/contents/clinical-features-and-diagnosis-of-chronic-fatigue-syndrome-systemic-exertion-intolerance-disease.
          5. About ME/CFS. National Institute of Health. February 6, 2017; https://www.nih.gov/mecfs/about-mecfs.
          6. Committee on the Diagnostic Criteria for Myalgic Encephalomyelitis/Chronic Fatigue Syndrome; Board on the Health of Select Populations; Institute of Medicine. Source Washington (DC): National Academies Press (US). Beyond Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Redefining an Illness. The National Academies Collection: Reports funded by National Institutes of Health. February, 2015; https://www.ncbi.nlm.nih.gov/pubmed/25695122.
          7. Twisk FN. Replacing Myalgic Encephalomyelitis and Chronic Fatigue Syndrome with Systemic Exercise Intolerance Disease Is Not the Way forward. Diagnostics (Basel). February 5, 2016; 6(1):
          8. Roberts JR. Chronic Fatigue Syndrome. Medscape Reference. August 29, 2018; https://emedicine.medscape.com/article/235980-overview.
          9. Margaret-Mary G. Wilson. Chronic Fatigue Syndrome. Merck Manuals. December 2008; https://www.merckmanuals.com/home/print/special_subjects/disorders_of_unknown_cause/chronic_fatigue_syndrome.html. Accessed 8/4/2015.
          10. Diagnosis and Treatment of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome. Agency for Healthcare Research and Quality. December 2014, Addendum July 2016; https://effectivehealthcare.ahrq.gov/ehc/products/586/2004/chronic-fatigue-report-160728.pdf.

          Rare Infectious Disease News