Chronic Fatigue Syndrome

Medically reviewed by Carina Fung, PharmD, BCPPS

What is chronic fatigue syndrome?

Chronic fatigue syndrome1 (CFS) is a complex disorder characterized by severe fatigue (exhaustion). In particular, this fatigue:

  • Cannot be attributed to or explained by any underlying health condition
  • Does not resolve with rest (and may worsen with physical or mental activity)
  • Significantly reduces a patient’s ability to be active

As its name states, CFS is chronic (or long-term), usually lasting for more than six months2. The most common symptoms characteristic of CFS are muscle and joint pain, tenderness in the lymph nodes, sore throat, and cognitive difficulties.

People with chronic fatigue syndrome appear to be hypersensitive to even small amounts of exertion and activity. Because the effects of CFS can be so debilitating, many people with the condition are unable to perform their day-to-day activities as usual. When severe, CFS can leave one confined to bed for long periods of time. While people with CFS may not appear ill, the disorder is often disabling.

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How common is chronic fatigue syndrome?

It is estimated that about 90% of people with chronic fatigue syndrome3 have not been diagnosed with the disorder. There are a variety of reasons4 for this:

  • There is no one test used to diagnose CFS, and its signs and symptoms can mimic those of other diseases.
  • CFS is often misunderstood. A patient’s experiences may not be taken as seriously as they should by some healthcare providers.
  • Most medical schools in the United States don’t include CFS in their physician training.

Because so many people with CFS don’t know they have it, it can be difficult to determine the actual prevalence of the disease. According to the CDC, however, one report estimates that some 836,000 to 2.5 million Americans3 live with chronic fatigue syndrome.

While the disorder can affect anyone at any age, CFS is most common in people between the ages of 40 and 603 and is more common in women than in men.

Chronic fatigue syndrome causes

Scientists have not yet discovered the exact cause5 of chronic fatigue syndrome. Some experts believe that people with CFS may be born with a higher genetic predisposition for the disorder, which is then triggered by various environmental factors.

Potential triggers6 of chronic fatigue syndrome include:

  • Viral infections: Some people develop CFS after having a viral infection. While no conclusive evidence connecting the two has been found, some viruses that have been posited as potential contributors to the development of CFS include Epstein-Barr virus, and human herpesvirus 6.
  • Changes in the immune system: It seems possible that CFS is caused by a change in the immune system and the ways it responds to stress or infection. CFS has some of the same features as autoimmune disorders (diseases in which the immune system mistakenly attacks its own healthy tissues, such as rheumatoid arthritis and type 1 diabetes).

It’s uncertain, however, whether the slight immune impairment seen in people with CFS is enough to cause the disease.

  • Stress and hormonal imbalance: Many patients with CFS report experiencing physical or emotional stress7 before falling ill. Both forms of stress affect the hypothalamic-pituitary-adrenal axis (HPA axis), a complex network of glands that control the body’s reaction to stress and regulate many processes, including the immune response.

These glands release a number of hormones, including cortisol (the “stress hormone,” which helps to decrease inflammation and suppress immune activity). Some patients with CFS have been found to have lower levels of cortisol, which may contribute to the increased inflammation and hyperactive immune system seen in chronic fatigue syndrome.

  • Genetics: While the particular genes responsible for CFS have not yet been identified, certain studies have suggested that inherited factors (in conjunction with environmental factors) may play a role in the development of CFS.

Risk factors for chronic fatigue syndrome

Certain factors8 may increase your risk of developing chronic fatigue syndrome, including:

  • Age: While CFS can affect anyone at any age, it most commonly affects people between the ages of 40 and 60.
  • Biological sex: Women are diagnosed with CFS much more frequently than men. It has not yet been determined, however, whether this is due to biological factors or the fact that women are more likely to share their symptoms with their healthcare providers.
  • Stress: Poor stress management may contribute to the development of CFS.

Chronic fatigue syndrome symptoms

As its name suggests, chronic fatigue syndrome causes severe, constant exhaustion and fatigue. This fatigue is disabling to the point that people with CFS are unable to function as they did before developing the disease.

In people with CFS, everyday tasks like bathing, cooking, or doing laundry are so taxing that they cause periods of exhaustion (called post-exertional malaise [PEM]). This can make responsibilities and commitments like work, school, and socialization incredibly difficult to complete. Some people with CFS (at least one in four9) have such severe symptoms that they are bedridden or housebound or long periods of time.

The symptoms9 of CFS are generally broken up into primary symptoms (those that are required for diagnosis and present in all patients with CFS) and other symptoms that only some patients with CFS will experience.

Primary symptoms of CFS

The primary (or “core”) symptoms10 of chronic fatigue syndrome include:

Significantly reduced ability to complete activities that were normal prior to the disease: This occurs alongside fatigue and must last for at least six months.

While everyone feels exhausted from time to time, CFS feels different. The fatigue seen in CFS:

  • Is often severe
  • Is not caused by high levels of exertion or difficult activities
  • Was not present before developing the disease
  • Does not improve with rest or sleep

Post-exertional malaise (PEM): This period of worsened symptoms following normal levels of physical or mental exertion is often described as a “crash,” “collapse,” or “relapse.” PEM is caused by normal activities, such as grocery shopping or taking a shower, and can leave someone with CFS housebound or unable to do anything for days on end.

During PEM, the symptoms of CFS may worsen or appear, including:

  • Cognitive difficulties
  • Sleep disturbances
  • Sore throat
  • Dizziness
  • Headaches
  • Severe exhaustion

Sleep disturbances: People with CFS may find that even a full night’s sleep doesn’t help improve their exhaustion or fatigue. Some may also have difficulty falling or staying asleep.

In addition to the three primary symptoms, at least one of the two following symptoms must be present in order for an individual to be diagnosed with CFS:

  • Orthostatic intolerance11: Lightheadedness, dizziness, weakness, or feeling faint that appear or are worsened while standing or sitting up. This may also be accompanied by vision changes, such as blurriness or seeing white or black spots.
  • Memory or cognition problems: Many people with CFS describe experiencing “brain fog” that prevents them from thinking clearly. This can include difficulties with memory, quick thinking, and paying attention to details.

Other common symptoms of CFS

Some people with chronic fatigue syndrome may experience the following in addition to their primary symptoms:

  • Pain: While it’s very common for people with CFS to experience pain, the type, location, and severity of this pain can differ from person to person.

    The most common types of pain in people with CFS are joint pain (without swelling or redness), muscle aches and pain, and new or worsening headaches. Some people with CFS may also have tender lymph nodes in the armpits or neck.

  • Digestive issues, such as irritable bowel syndrome (IBS)

  • Frequent sore throat

  • Chills and night sweats

  • Allergy or sensitivity to certain foods, smells, chemicals, light (photosensitivity), or noise (phonosensitivity)

  • Muscle weakness

  • Shortness of breath

  • Irregular heartbeat (arrhythmia)

The signs and symptoms of chronic fatigue syndrome can be unpredictable. They may come and go and vary from mild to severe. If you experience any of the signs or symptoms of CFS, talk to your healthcare provider. They will be able to provide the correct diagnosis and treatment.

Complications from chronic fatigue syndrome

Especially when untreated, CFS can lead to a number of complications12, including:

  • Mental health disorders: Living with a chronic, disabling illness can make everyday life difficult. Many patients with CFS develop depression, while some also develop stress and/or anxiety.
  • Absence from work or school: The extreme exhaustion and fatigue experienced in CFS can make it impossible to regularly attend classes or work.
  • Social isolation: As with work or school, social activities may be difficult to attend during periods of severe fatigue.
  • Reduction in quality of life: The challenges of living with CFS can cause a substantial decline in the quality of one’s day-to-day life.

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