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Symptoms and Signs of Chronic Fatigue Syndrome

Doctor's Notes on Chronic Fatigue Syndrome (CFS)

Chronic fatigue syndrome (CFS) is a condition characterized by pronounced fatigue for at least six months in the absence of known medical causes along with other characteristic symptoms. The Institute of Medicine (IOM) recommends the name systemic exertion intolerance disease (SEID) for this disease.  The cause of CFS is poorly understood. Some researchers believe that the condition is an endpoint for many different disease processes such as viral infections, toxin exposure, and stress

Associated symptoms and signs in addition to fatigue include poor concentration, memory problems, sore throat, muscle pain, tender lymph nodes, malaise, headache, and poor sleep quality. Other symptoms can include mild fever, earache, diarrhea, dizziness, depression, mood changes, chills, vision disturbances, and food sensitivities.

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Medically Reviewed on 3/11/2019

Chronic Fatigue Syndrome (CFS) Symptoms

Diagnosing CFS requires ruling out other causes of chronic persistent fatigue, including a stressful lifestyle, cancer, or other illness such as adrenal or thyroid disorders, HIV, or AIDS. Since there are no laboratory tests that specifically make the diagnosis of CFS, the diagnosis is based on symptoms. People with CFS experience the following symptoms:

  • Fatigue: People with CFS have long-term fatigue (lasting longer than 6 months to a year) that cannot be explained by other diseases. People with CFS may have had a previous infection. They are tired and "run down" during the infection, and the fatigue continues after the person has recovered from the illness.
  • Cognitive difficulties: A typical complaint of people with CFS is that they have problems with short-term memory but not long-term memory. People with CFS may have problems finding or saying a particular word during normal speech (called dysnomia or verbal dyslexia).
  • Postexertional fatigue: Postexertional fatigue may also be a problem for people with CFS. They are excessively tired after doing normal activities that were not difficult in the past.
  • Fatigue after sleep: People with CFS also complain of fatigue even after long periods of rest or sleep. They do not feel refreshed after sleeping.
  • Depression: People with CFS may become depressed because of difficulties performing at work or home, but depression does not cause CFS.
  • Other symptoms that may be seen include headaches, muscle aches, sore throat, and even mild fever.

Chronic Fatigue Syndrome (CFS) Causes

The cause of CFS is unknown, but the condition may be related to infection with effects on the immune system. Several viruses have been studied as possible causes of CFS, but no cause-and-effect relationship has been discovered. Some evidence indicates that the bacterium Chlamydia pneumoniae (which causes pneumonia and other illnesses) may be a cause of CFS in some cases. People with chronic fatigue syndrome related to C. pneumoniae are most likely to respond to antibiotics that kill C. pneumoniae, and their CFS symptoms may improve with antibiotic medications such as doxycycline. However, this association is still being debated. Various unrelated infections appear to lead to long-term fatigue in some people. If the fatigue is accompanied by problems with short-term memory or concentration, CFS is possible.

  • One of the associated infections is the Epstein-Barr virus, or EBV. EBV causes mononucleosis, also called "mono" or the "kissing disease." Although associated in some cases, EBV does not cause CFS, and CFS is not the same thing as long-term EBV infection or long-term mononucleosis.
  • Other unrelated infectious diseases that appear to lead to fatigue include pneumonia, diarrhea, and bronchitis.
  • Candida albicans infections (or yeast infections) do not cause CFS.

Other conditions that cause symptoms similar to those of CFS must be ruled out. These include the following:

Chronic Fatigue Syndrome (CFS) Symptoms and Diagnosis Slideshow

Chronic Fatigue Syndrome (CFS) Symptoms and Diagnosis Slideshow

Chronic fatigue syndrome (CFS, also called chronic fatigue immune dysfunction syndrome, or CFIDS) is a chronic disorder characterized by several debilitating conditions including severe fatigue. Other symptoms include weakness, impaired memory or concentration, insomnia, muscle pain, and fatigue following exertion that lasts more than 24 hours. The causes of CFS are unknown, and there is no specific test to diagnose the condition. It is diagnosed through exclusion, that is, ruling out other illnesses with similar symptoms.


Kasper, D.L., et al., eds. Harrison's Principles of Internal Medicine, 19th Ed. United States: McGraw-Hill Education, 2015.