Chronic fatigue syndrome
Description
An in-depth report on the causes, diagnosis, and treatment of chronic fatigue syndrome.
Risk Factors
In studies of large patient groups, 15 - 27% of people complain of long-term fatigue, but the majority can be explained by other medical or psychological problems. According to surveys, chronic fatigue syndrome (CFS) itself affects over four in every 1,000 Americans. It occurs in both sexes and at all ages and in all racial and ethnic groups. The CDC estimates 1 million people in the U.S. have the disease, but only 20% of people with CFS may be properly diagnosed. Nevertheless, the true prevalence of CFS is very difficult to determine, since an accurate diagnosis is difficult to obtain.
Age and Gender
Chronic fatigue is most often experienced by individuals 40 - 50 years old. Studies have found that four times the number of women than men have CFS, although women do not appear to have more severe symptoms than men with the disorder. Children and adolescents are not immune to its effects. Most studies indicate that girls are more likely to develop CFS than boys, although one study found the incidence of the syndrome to be equal.
Culture and Social Levels
Some studies report that CFS rates are highest in minority groups (African and Hispanic Americans), and people with lower levels of education and occupational status. Other studies found higher rates of CFS in Caucasian women than in women from other ethnic groups. However, this may reflect the greater socioeconomic ability of Caucasian women to seek treatment.
Depression and Psychological Factors
The link between psychological disorders and chronic fatigue syndrome is problematic because so many of the symptoms overlap. The rates of depression are very high in CFS patients. In one study, 27.4% of patients diagnosed with CFS alone also had a history of depression. (Depression rates were significantly higher in CFS patients who had other conditions, notably fibromyalgia and multiple chemical sensitivity.)
Studies also report that most children and adolescents with CFS suffer psychiatric disorders. Some evidence suggests that psychological factors during childhood may increase susceptibility for later CFS, although these factors are not consistent. For example, in a small 2003 survey, CFS patients tended to have mothers who were overprotective and depressed. In another small study, five out of 13 patients reported sexual or physical abuse during childhood. The bottom line is that studies have not found any consistent association between emotional or personality disorders and CFS to explain any causal role. Some may however, serve as a risk factor for CFS.
Depression, in any case, is very common in the general population. It affects up to one-fifth of all Americans at some point in their lives, and most depressed people feel fatigued.
Stress
There is some evidence that stress may be a trigger for CFS in people genetically at-risk for the disease. A long-term study of twins in Sweden, reported in 2006, found that higher emotional instability and self-reported stress were associated with higher risk of developing a CFS-type illness.
Conditions That Commonly Occur in CFS Patients
A number of conditions overlap or co-exist with chronic fatigue syndrome and have similar symptoms. In fact, in one study of patients with CFS only 38% of patients had a sole diagnosis. The others also had fibromyalgia, multiple chemical sensitivity, or both. It is not clear if these conditions or others are risk factors for CFS, are direct causes, have common causes, or have no relationship at all with CFS.
Fibromyalgia.
Fibromyalgia causes prolonged fatigue and widespread muscle aches and is the disease most often confused with CFS. They also commonly appear together. In one study, for example, 37% of patients who met the criteria for CFS also had a co-diagnosis of fibromyalgia. In fact, many experts believe fibromyalgia is simply another variant of chronic fatigue syndrome or different manifestations of the same disease, with CFS patients experiencing severe fatigue while fibromyalgia patients experience more pain. There is a hypothesis that the connection may be found in central sensitization, which is known to cause fibromyalgia and may also cause CFS.
A characteristic feature of fibromyalgia is the existence of at least 11 distinct sites of deep muscle tenderness that hurt when touched firmly. The sites often include the following:
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The side of the neck
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The top of the shoulder blade
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The outside of the upper buttock and hip joint
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The inside of the knee
Some patients with CFS exhibit similar tender pressure points. Recurrent sore throat, headache, low fever, and depression are also common symptoms of fibromyalgia. Like CFS, fibromyalgia is chronic and not curable.
Multiple Chemical Sensitivity.
Multiple chemical sensitivity (MCS) is a term now used to describe a condition in which certain chemicals can cause symptoms similar to CFS in some people. It has also been observed in people with CFS. Experts have come up with criteria to help recognize people with MCS.
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The symptoms are reproducible with repeated exposure to a chemical. (These are often common chemicals found in popular products, such as perfumes, fabric softeners, and air fresheners.)
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The condition is chronic.
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Symptoms can be produced by exposure to the chemical at levels lower than previously or commonly tolerated.
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The symptoms improve when the chemical is removed.
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Symptoms can be triggered by multiple substances that are chemically unrelated.
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Symptoms involve multiple organ systems.
Still, as with CFS and fibromyalgia, some experts are uncertain whether MCS is an actual medical condition or is psychologically based. In one study, for example, CFS patients who believed their problem was chemically triggered were exposed to either an active chemical or a placebo (an inactive substance). Both groups reported symptoms, including those exposed only to the placebo. It should be noted that everyone is exposed to many chemicals on a daily basis, and it is very difficult to determine if chemicals are responsible for specific symptoms.
Eating Disorders.
Eating disorders, notably bulimia and anorexia, have been observed in patients with CFS. In one small study, CFS occurred after the development of the eating disorder. It is not clear if there was a causal relationship. The conditions often have over-lapping risk factors, although whether there is a causal relationship is unclear.
Work-Related Fatigue and Burn-Out.
Many people who suffer burn-out or fatigue from employment have symptoms that are similar or even identical to CFS. One study of nurses, for example, found that those who were exposed to poor working conditions and threats of accidents faced a higher risk for CFS symptoms than those without these experiences. However, work-related CFS symptoms are usually of much shorter duration. It they persist, however, doctors should not rule out CFS.
Other Conditions that Commonly Co-exist With CFS.
A number of other conditions also often co-exist with CFS and, in fact, occur at higher-than-average rates among CFS patients:
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Temporomandibular disorder (TMD)
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Irritable bowel syndrome
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Chronic headaches
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Interstitial cystitis
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Hypothyroidism
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Sjögren syndrome
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Sleep problems
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Cognitive problems such as difficulty concentrating, impaired memory, and symptoms of attention deficit disorders
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Review Date: 1/4/2007
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Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital
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