Fibromyalgia - Causes

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Brain Chemicals and Hormonal Abnormalities

Studies of hormonal, metabolic, and brain chemical activity in fibromyalgia patients have shown numerous abnormalities. Changes appear to occur in several brain chemicals, although no regular pattern has emerged that fits most patients. Some experts believe that the changes are a result of the effects of pain and stress on the central nervous system, and are not a cause of fibromyalgia.

Serotonin. Of particular interest to researchers is serotonin, an important nervous system chemical messenger found in the brain, gut, and other areas of the body. Serotonin plays important roles in feelings of well-being, adjusting pain levels, and promoting deep sleep. Serotonin abnormalities have been linked to many disorders, including depression, migraines, and irritable bowel syndrome. Lower serotonin levels have also been noted in some patients with fibromyalgia.

Stress Hormones. Researchers have also found abnormalities in the hormone system known as the hypothalamus-pituitary-adrenal gland (HAP) axis. The HAP axis controls important functions, including sleep, response to stress, and depression. Changes in the HAP axis appear to produce lower levels of the stress hormones norepinephrine and cortisol. (By contrast, levels of stress hormones in depression are higher than normal.) Deficiencies in the levels of stress hormones produce impaired and weaker responses to psychological or physical stresses. (Examples of physical stress include infection or exercise.)

Click the icon to see an image of the adrenal glands.

Low Growth Hormone Levels. Some studies have reported low levels of insulin-like growth factor-1 (IGF-1) in about a third of fibromyalgia patients. IGF-1 is a hormone that is controlled by the adult growth hormone, and promotes bone and muscle growth. Low levels of growth hormone are related to impaired thinking, lack of energy, muscle weakness, and intolerance to cold. Severe growth hormone deficiency has been observed in a subset of fibromyalgia patients. While researchers did not find a link between IGF-1 levels and fibromyalgia, a 2005 study indicates that serum growth hormone levels may be a marker of the disorder.