In studies of large patient groups, 15 - 27% of people complain of long-term fatigue, but the majority of this fatigue can be explained by other medical or psychological problems. According to surveys, chronic fatigue syndrome (CFS) itself affects more than four out of every 1,000 Americans.
CFS occurs in both sexes, at all ages, and in all racial and ethnic groups. The Centers for Disease Control and Prevention (CDC) estimates that between 1 and 4 million people in the U.S. have the disease, but only half of people with CFS have seen their doctor for the condition. About 40% of people who report symptoms of CFS have another medical or psychiatric condition, according to the CDC.
People ages 40 - 50 most often experience chronic fatigue. Studies have found that four out of five people with CFS are women, although women do not appear to have more severe symptoms than men with the disorder.
Children and adolescents can also have CFS. Most studies indicate that girls are more likely than boys to develop CFS, although one study found the incidence of the syndrome to be equal in children of both genders.
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, possibly higher than in patients with other conditions (notably fibromyalgia and multiple chemical sensitivity).
Studies report that most children and adolescents with CFS have psychiatric disorders. Psychological factors during childhood may increase susceptibility for CFS later in life, although studies have not found any consistent association between emotional or personality disorders and CFS to explain any causal role. Some psychological factors may, however, be risk factors for CFS.
Depression 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.
There is some evidence that stress may trigger CFS in people who are genetically at risk for the disease.
A number of conditions overlap or coexist with chronic fatigue syndrome and have similar symptoms. Patients with CFS may also have a diagnosis of fibromyalgia, multiple chemical sensitivity, or both. It is not clear whether these and other conditions 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. It is the disease most often confused with CFS. The two conditions also commonly appear together. In fact, many experts believe fibromyalgia is simply another variant of chronic fatigue syndrome or they are different manifestations of the same disease. CFS patients experience severe fatigue, whereas fibromyalgia patients experience more pain. One hypothesis is that the connection between the two conditions may be found in central sensitization, which is thought 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:
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 are believed to cause symptoms similar to CFS in some people. MCS has also been observed in people with CFS. The following proposed criteria can help recognize people with MCS:
As with CFS and fibromyalgia, there is uncertainty as to 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 whether chemicals are responsible for specific symptoms.
Eating Disorders. Eating disorders, notably bulimia and anorexia, have been observed in patients with CFS. The conditions often have overlapping risk factors, although it is unclear whether one causes the other.
Other Conditions that Commonly Coexist With CFS. A number of other conditions also may coexist with CFS and occur at higher-than-average rates among CFS patients:
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