What causes chronic fatigue syndrome?
The exact cause of chronic fatigue syndrome remains a mystery. Although the illness sometimes occurs after an infection with B. burgdorferi (Lyme disease bacteria) or an episode of infectious mononucleosis, there is no proof that these infections cause chronic fatigue syndrome. Researchers also have been unable to link chronic fatigue syndrome to immune system problems or allergies. So far, the most promising theory describes chronic fatigue syndrome as a multisystem disorder that disturbs the complex relationship between the hypothalamus (a part of the brain that regulates
hormones and vital functions) and the pituitary and adrenal glands. This theory is supported by studies that link chronic fatigue syndrome to a form of a condition called neurally mediated hypotension, which is abnormally low blood pressure caused by a problem in the nervous system. The most recent studies, however, have found no consistent connection between low blood pressure and chronic fatigue, so the role of brain function and blood pressure regulation to the condition remains uncertain.
Abnormalities in the central nervous system, including pinpoint spots of brain inflammation and abnormal levels of certain hormones, have been reported in a number of patients with chronic fatigue syndrome, but similar findings have also been found in those without the illness. Because most of the features of chronic fatigue syndrome resemble those of a lingering viral illness, many researchers have focused on the possibility that a virus or some other infectious agent causes the syndrome in some cases. Chronic fatigue syndrome has sometimes been referred to as the "chronic fatigue immune dysfunction syndrome." A number of studies have found many irregularities of the immune system, although there is no consistent pattern. Some components appear to be overreactive, whereas others appear to be underreactive. Some studies have observed that a subgroup of patients who fit the strict criteria for chronic fatigue syndrome also have a condition known as neurally mediated hypotension (NMH). NMH causes a dramatic drop in blood pressure when standing up, even for as short a time as ten minutes. Some experts believe that chronic fatigue syndrome is a disorder of the sleep-wake cycle. (They argue that some mentally or physically stressful event, such as a viral infection, may disrupt natural circadian rhythms, and that an inability to reset these rhythms results in a perpetual cycle of sleep disturbances. Psychological, personality, and social factors are strongly associated with chronic fatigue in most, but not all, patients.
Although the cause is still controversial, many doctors and researchers now think that chronic fatigue syndrome may not be a single illness. Instead, they think chronic fatigue syndrome may be a group of symptoms caused by several conditions. One theory is that a microorganism, such as a virus, or a chemical injures the body and damages the immune system, allowing dormant viruses to become active. About 90% of all people have a virus in the herpes family dormant (not actively growing or reproducing) in their bodies since childhood. When these viruses start growing again, the immune system may overreact and produce chemicals called cytokines that can cause flu-like symptoms. Immune abnormalities have been found in studies of people with chronic fatigue syndrome, although the same abnormalities are also found in people with allergies, autoimmune diseases, cancer, and other disorders.
The role of psychological problems in chronic fatigue syndrome is very controversial. Because many people with chronic fatigue syndrome are diagnosed with depression and other psychiatric disorders, some experts conclude that the symptoms of chronic fatigue syndrome are psychological. However, many people with chronic fatigue syndrome did not have psychological disorders before getting the illness. Many doctors think that patients become depressed or anxious because of the effects of the symptoms of their chronic fatigue syndrome. One recent study concluded that depression was the result of chronic fatigue syndrome and was not its cause.