Chronic Fatigue Syndrome - What Causes Fatigue: Chronic Fatigue

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Chronic fatigue syndrome

Although chronic fatigue syndrome (CFS) is the first illness that some people think of when they're weak and exhausted for no apparent reason, it accounts for just 3% of all cases of persistent fatigue. Twice as many women as men have it. About 4 out of every 1,000 adults in the United States suffer from the condition. The illness also occurs in teenagers and younger children, although it is less common in these age groups.

The causes of CFS are unknown, and there is no accurate diagnostic test. The illness is defined by a set of symptoms established by the U.S. Centers for Disease Control and Prevention. Doctors diagnose CFS by looking for these symptoms and ruling out other possible causes, such as depression or another medical condition.

Symptoms of CFS

The symptoms of CFS tend to wax and wane, but most people remain impaired to some degree even on their good days. The illness is defined by a severe and debilitating fatigue that lasts for six months or longer and is not relieved by rest, plus at least four of the following, also for at least six months:

• impaired memory or concentration

• sore throat

• swollen glands

• pain in muscles or joints

• headaches that are different in some way from any experienced before

• tiredness even after sleeping

• exhaustion following physical exertion.

Unlike other causes of persistent fatigue, which come on gradually, CFS tends to appear suddenly. Often it begins with a flu-like illness. Although several infectious agents have been linked with CFS, none have been proved to cause CFS. And some cases may have no infectious cause.

Although the cause of CFS is unknown, it appears to have a physical basis. Many scientific studies have reported measurable abnormalities, primarily in the brain but also in the immune and hormonal systems. However, doctors have not yet found any abnormality common to all patients that could be used as a reliable diagnostic test.

CFS and depression

Some doctors have questioned whether CFS is a form of psychiatric illness, particularly depression. One reason for this is that patients with depression often develop fatigue and several of the other symptoms seen in CFS. But most people with CFS have no history of psychiatric illness in the years before developing CFS, and a substantial minority — 25% to 50% — don't develop depression even after the onset of their illness.

Another piece of evidence that CFS is not a manifestation of depression is that certain brain hormones that are often seen in people with depression are not seen in people with CFS. For example, in people with CFS, the brain makes lower than normal levels of cortisol, a stress hormone, whereas in people with depression, the brain makes higher than normal levels. In addition, one well-known study found that fluoxetine (Prozac) did not relieve either fatigue or depression in patients with CFS.

One particular kind of medication, tricyclic antidepressants, used in doses that are too low to relieve depression, seems to help relieve CFS symptoms, perhaps because the tricyclics are muscle relaxants and also increase the amount of deep, restorative sleep.

Explaining CFS

Many studies indicate that the symptoms of CFS are most likely caused by abnormalities in the brain, particularly in a part of the brain called the limbic system, as well as in the autonomic nervous system (ANS). The ANS is the part of the nervous system that controls vital automatic body functions such as blood pressure, heartbeat, and body temperature. Many patients with CFS show a tendency for the blood pressure to drop and the heartbeat to race when they stand up and remain on their feet after sitting or lying down. Doctors are testing various medications that might correct this condition.

It remains uncertain as to what triggers these nervous system abnormalities. Two related theories are that a persistent infection, with any of several different microbes, may cause the symptoms. An infection of the brain or autonomic nervous system could directly cause symptoms of CFS, while an infection affecting another part of the body could indirectly cause symptoms by triggering an immune response that alters brain chemistry. There are probably several types of triggers of CFS. For example, in some cases, people may develop CFS from a head trauma or exposure to an environmental toxin.

Many studies have found evidence that, in people with CFS, the immune system is chronically activated, as if it is engaged in battling some foreign invader. However, there is no evidence of an immune system deficiency that would make people with CFS especially vulnerable to infections or to cancer.

Treating CFS

Some people with CFS eventually recover (perhaps 50% or more of children, but only 15%–40% of adults). For others, certain treatments can help relieve the symptoms. If you have been told by a doctor that you have CFS, a combination of the following strategies may prove helpful:

Set priorities. Make a list of the things that you want to have more energy to do, and eliminate as many nonessential activities and obligations as you can. The goal is to conserve your energy for the most important activities in your life and to reduce the psychological stress and physical exhaustion that can come from being overscheduled and overextended. At the same time, guard against becoming too passive. Push yourself to your limits, and trust your body to know when you've reached those limits.

Exercise. An exercise program in which you gradually increase your activity level can be very effective in relieving symptoms. Before starting, keep a diary for a week or so, recording what you do and when. Many patients engage in bursts of vigorous activity when they feel able, but then pay for it afterward, becoming so fatigued that they are inactive for days or weeks. The goal of gradually increasing exercise is to eliminate such wide swings in activity. Choose exercise that is light enough that it doesn't cause exhaustion, but challenging enough that it's invigorating. A recent study by the Agency for Health Care Research and Quality found that exercise may help relieve fatigue and improve quality of life for people with CFS. The type of exercise did not seem to matter. More important than the particular exercise you choose is doing it almost daily. As your stamina increases, step up the intensity of your exercise regimen or the time you devote to it.

Cognitive behavioral therapy. This type of psychotherapy helps you identify and change negative thoughts and behaviors. Some of the patterns of thinking and behavior that people develop in response to their symptoms serve to aggravate those symptoms. For example, some people avoid exercise because they fear it will make them more fatigued. But lack of physical exercise can actually worsen the symptoms. Through cognitive behavioral therapy, patients explore ways to overcome such negative thought processes. But cognitive behavioral therapy requires an experienced therapist, and studies have been mixed regarding its effectiveness in treating CFS.

Tricyclic antidepressants. Many doctors who care for CFS patients believe that low doses of a tricyclic antidepressant may help CFS symptoms. This therapy seems to improve the quality of sleep, reduce pain, and increase energy. As yet, no scientific studies have been conducted of this treatment in patients with CFS, but studies have found a clear benefit in patients with a similar illness, fibromyalgia (see below).

Other medications. The headaches, joint pain, and muscle pain that characterize CFS can be relieved with nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen (Advil, Motrin) or naproxen (Aleve), or another over-the-counter analgesic, acetaminophen (Tylenol). CFS sufferers who also have allergies sometimes find that decongestants and other medications that help relieve their allergy symptoms also improve their CFS symptoms. But antihistamines, mainstays of allergy treatment, cause drowsiness in varying degrees and should be avoided during the day, although they can be useful if taken at bedtime. There is some evidence that fish oil capsules (3,000 mg per day is a good dose) may also help reduce the symptoms of CFS. Low doses of the stimulant drug modafinil (Provigil) may help some patients, although this has not been proven in a scientific study.

Experimental treatments. Among experimental approaches currently being explored are medications to address abnormalities of the autonomic nervous system that cause low blood pressure and rapid heartbeat. Thus far, such treatments have not proved effective.

Last updated:	January 23, 2007