Introduction

Chronic fatigue syndrome, or CFS, is a debilitating and complex disorder characterized by profound fatigue that is not improved by bed rest and that may be worsened by physical or mental activity. Persons with CFS most often function at a substantially lower level of activity than they were capable of before the onset of illness. In addition to these key defining characteristics, patients report various nonspecific symptoms, including weakness, muscle pain, impaired memory and/or mental concentration, insomnia, and post-exertional fatigue lasting more than 24 hours. In some cases, CFS can persist for years. The cause or causes of CFS have not been identified and no specific diagnostic tests are available. Moreover, since many illnesses have incapacitating fatigue as a symptom, care must be taken to exclude other known and often treatable conditions before a diagnosis of CFS is made.

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Definition of CFS

A great deal of debate has surrounded the issue of how best to define CFS. In an effort to resolve these issues, an international panel of CFS research experts convened in 1994 to draft a definition of CFS that would be useful both to researchers studying the illness and to clinicians diagnosing it. In essence, in order to receive a diagnosis of chronic fatigue syndrome, a patient must satisfy two criteria:

1. Have severe chronic fatigue of six months or longer duration with other known medical conditions excluded by clinical diagnosis; and
2. Concurrently have four or more of the following symptoms: substantial impairment in short-term memory or concentration; sore throat; tender lymph nodes; muscle pain; multi-joint pain without swelling or redness; headaches of a new type, pattern or severity; unrefreshing sleep; and post-exertional malaise lasting more than 24 hours.

The symptoms must have persisted or recurred during six or more consecutive months of illness and must not have predated the fatigue.

For more detailed information regarding the definition of CFS, please go to our CFS Definition section.

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Similar Medical Conditions

A number of illnesses have been described that have a similar spectrum of symptoms to CFS. These include fibromyalgia syndrome, myalgic encephalomyelitis, neurasthenia, multiple chemical sensitivities, and chronic mononucleosis. Although these illnesses may present with a primary symptom other than fatigue, chronic fatigue is commonly associated with all of them.

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Other Conditions That May Cause Similar Symptoms

In addition, there are a large number of clinically defined, frequently treatable illnesses that can result in fatigue. Diagnosis of any of these conditions would exclude a definition of CFS unless the condition has been treated sufficiently and no longer explains the fatigue and other symptoms. These include hypothyroidism, sleep apnea and narcolepsy, major depressive disorders, chronic mononucleosis, bipolar affective disorders, schizophrenia, eating disorders, cancer, autoimmune disease, hormonal disorders*, subacute infections, obesity, alcohol or substance abuse, and reactions to prescribed medications.

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Other Commonly Observed Symptoms in CFS

In addition to the eight primary defining symptoms of CFS, a number of other symptoms have been reported by some CFS patients. The frequencies of occurrence of these symptoms vary from 20% to 50% among CFS patients. They include abdominal pain, alcohol intolerance, bloating, chest pain, chronic cough, diarrhea, dizziness, dry eyes or mouth, earaches, irregular heartbeat, jaw pain, morning stiffness, nausea, night sweats, psychological problems (depression, irritability, anxiety, panic attacks), shortness of breath, skin sensations, tingling sensations, and weight loss.

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Risk Factors for CFS

• People of every age, gender, ethnicity and socioeconomic group can have CFS.
• CFS affects women at four times the rate of men.
• Research indicates that CFS is most common in people in their 40s and 50s.
• Although CFS is much less common in children than in adults, children can develop the illness, particularly during the teen years.

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Defining CFS Symptoms

• CFS is marked by extreme fatigue that has lasted at least six months; is not the result of ongoing effort; is not substantially relieved by rest; and causes a substantial reduction in daily activities.
• In addition to fatigue, CFS includes eight characteristic symptoms:
  • postexertional malaise (relapse of symptoms after physical or mental exertion);
  • unrefreshing sleep;
  • substantial impairment in memory/concentration;
  • muscle pain;
  • pain in multiple joints;
  • headaches of a new type, pattern or severity;
  • sore throat; and
  • tender neck or armpit lymph nodes.
• Symptoms and their consequences can be severe. CFS can be as disabling as multiple sclerosis, lupus, rheumatoid arthritis, congestive heart failure and similar chronic conditions. Symptom severity varies from patient to patient and may vary over time for an individual patient.

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Diagnosis of CFS

• There are no physical signs that identify CFS
• There are no diagnostic laboratory tests for CFS.
• People who suffer the symptoms of CFS must be carefully evaluated by a physician because many treatable medical and psychiatric conditions are hard to distinguish from CFS. Common conditions that should be ruled out through a careful medical history and appropriate testing include mononucleosis, Lyme disease, thyroid conditions, diabetes, multiple sclerosis, various cancers, depression and bipolar disorder.
• Research conducted by the Centers for Disease Control and Prevention (CDC) indicates that less than 20% of CFS patients in this country have been diagnosed.

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Treatment of CFS

• Since there is no known cure for CFS, treatment is aimed at symptom relief and improved function. A combination of drug and nondrug therapies is usually recommended.
• No single therapy exists that helps all CFS patients.
• Lifestyle changes, including prevention of overexertion, reduced stress, dietary restrictions, gentle stretching and nutritional supplementation, are frequently recommended in addition to drug therapies used to treat sleep, pain and other specific symptoms.
• Carefully supervised physical therapy may also be part of treatment for CFS. However, symptoms can be exacerbated by overly ambitious physical activity. A very moderate approach to exercise and activity management is recommended to avoid overactivity and to prevent deconditioning.
• Although health care professionals may hesitate to give patients a diagnosis of CFS for various reasons, it’s important to receive an appropriate and accurate diagnosis to guide treatment and further evaluation.
• Delays in diagnosis and treatment are thought to be associated with poorer long-term outcomes. For example, CDC’s research has shown that those who have CFS for two years or less were more likely to improve. It’s not known if early intervention is responsible for this more favorable outcome; however, the longer a person is ill before diagnosis, the more complicated the course of the illness appears to be.

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Recovery from CFS

• CFS affects each individual differently. Some people with CFS remain homebound and others improve to the point that they can resume work and other activities, even though they continue to experience symptoms.
• Recovery rates for CFS are unclear. Improvement rates varied from 8% to 63% in a 2005 review of published studies, with a median of 40% of patients improving during follow-up. However, full recovery from CFS may be rare, with an average of only 5% to 10% sustaining total remission.

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Possible Causes of CFS

• Despite an intensive, nearly 20-year search, the cause of CFS remains unknown. Many different infectious agents and physiologic and psychological causes have been considered, and the search continues.
• Much of the ongoing research into a cause has centered on the roles of the immune, endocrine and nervous systems may play in CFS. More recently, interactions among these factors are under evaluation.
• Genetic and environmental factors may play a role in developing and/or prolonging the illness, although more research is needed to confirm this. CDC is applying cutting-edge genomic and proteomic tools to understand the origins and pathogenesis of CFS.
• CFS is not caused by depression, although the two illnesses often coexist, and many patients with CFS have no psychiatric disorder.

 

Infectious Agents

Due in part to its similarity to chronic mononucleosis, CFS was initially thought to be caused by a virus infection, most probably Epstein-Barr virus (EBV). It now seems clear that CFS cannot be caused exclusively by EBV or by any single recognized infectious disease agent. No firm association between infection with any known human pathogen and CFS has been established. CDC's four-city surveillance study found no association between CFS and infection by a wide variety of human pathogens, including EBV, human retroviruses, human herpesvirus 6, enteroviruses, rubella, Candida albicans, and more recently bornaviruses and Mycoplasma. Taken together, these studies suggest that among identified human pathogens, there appears to be no causal relationship for CFS. However, the possibility remains that CFS may have multiple causes leading to a common endpoint, in which case some viruses or other infectious agents might have a contributory role for a subset of CFS cases.

Immunology

It has been proposed that CFS may be caused by an immunologic dysfunction, for example inappropriate production of cytokines, such as interleukin-1, or altered capacity of certain immune functions. One thing is certain at this juncture: there are no immune disorders in CFS patients on the scale traditionally associated with disease. Some investigators have observed anti-self antibodies and immune complexes in many CFS patients, both of which are hallmarks of autoimmune disease. However, no associated tissue damage typical of autoimmune disease has been described in patients with CFS. The opportunistic infections or increased risk for cancer observed in persons with immunodeficiency diseases or in immunosuppressed individuals is also not observed in CFS. Several investigators have reported lower numbers of natural killer cells or decreased natural killer cell activity among CFS patients compared with healthy controls, but others have found no differences between patients and controls.

T-cell activation markers have also been reported to have differential expression in groups of CFS patients compared with controls, but again, not all investigators have consistently observed these differences. One intriguing hypothesis is that various triggering events, such as stress or a viral infection, may lead to the chronic expression of cytokines and then to CFS. Administration of some cytokines in therapeutic doses is known to cause fatigue, but no characteristic pattern of chronic cytokine secretion has ever been identified in CFS patients. In addition, some investigators have noted clinical improvement in patients with continued high levels of circulating cytokines; if a causal relationship exists between cytokines and CFS, it is likely to be complex. Finally, several studies have shown that CFS patients are more likely to have a history of allergies than are healthy controls. Allergy could be one predisposing factor for CFS, but it cannot be the only one, since not all CFS patients have it.

Hypothalamic-Pituitary Adrenal (HPA) Axis

Multiple laboratory studies have suggested that the central nervous system may have an important role in CFS. Physical or emotional stress, which is commonly reported as a pre-onset condition in CFS patients, activates the hypothalamic-pituitary-adrenal axis, or HPA axis, leading to increased release of cortisol and other hormones. Cortisol and corticotrophin-releasing hormone (CRH), which are also produced during the activation of the HPA axis, influence the immune system and many other body systems. They may also affect several aspects of behavior. Recent studies revealed that CFS patients often produce lower levels of cortisol than do healthy controls. Similar hormonal abnormalities have been observed by others in CFS patients and in persons with related disorders like fibromyalgia. Cortisol suppresses inflammation and cellular immune activation, and reduced levels might relax constraints on inflammatory processes and immune cell activation. As with the immunologic data, the altered cortisol levels noted in CFS cases fall within the accepted range of normal, and only the average between cases and controls allows the distinction to be made. Therefore, cortisol levels cannot be used as a diagnostic marker for an individual with CFS. A placebo-controlled trial, in which 70 CFS patients were randomized to receive either just enough hydrocortisone each day to restore their cortisol levels to normal or placebo pills for 12 weeks, concluded that low levels of cortisol itself are not directly responsible for symptoms of CFS, and that hormonal replacement is not an effective treatment. However, additional research into other aspects of neuroendocrine correlates of CFS is necessary to fully define this important, and largely unexplored, field.

Neurally Mediated Hypotension

Rowe and coworkers conducted studies to determine whether disturbances in the autonomic regulation of blood pressure and pulse (neurally mediated hypotension, or NMH) were common in CFS patients. The investigators were alerted to this possibility when they noticed an overlap between their patients with CFS and those who had NMH. NMH can be induced by using tilt table testing, which involves laying the patient horizontally on a table and then tilting the table upright to 70 degrees for 45 minutes while monitoring blood pressure and heart rate. Persons with NMH will develop lowered blood pressure under these conditions, as well as other characteristic symptoms, such as lightheadedness, visual dimming, or a slow response to verbal stimuli. Many CFS patients experience lightheadedness or worsened fatigue when they stand for prolonged periods or when in warm places, such as in a hot shower. These conditions are also known to trigger NMH. One study observed that 96% of adults with a clinical diagnosis of CFS developed hypotension during tilt table testing, compared with 29% of healthy controls. Tilt table testing also provoked characteristic CFS symptoms in the patients. A study (not placebo-controlled) was conducted to determine whether medications effective for the treatment of NMH would benefit CFS patients. A subset of CFS patients reported a striking improvement in symptoms, but not all patients improved. A placebo-controlled trial of NMH medications for CFS patients is now in progress.

Nutritional Deficiency

There is no published scientific evidence that CFS is caused by a nutritional deficiency. Many patients do report intolerances for certain substances that may be found in foods or over-the-counter medications, such as alcohol or the artificial sweetener aspartame. While evidence is currently lacking for nutritional defects in CFS patients, it should also be added that a balanced diet can be conducive to better health in general and would be expected to have beneficial effects in any chronic illness.