Fibromyalgia - Causes

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

Stress Hormones. Researchers have also noted abnormalities in the hormone system known as the hypothalamus-pituitary-adrenal gland (HPA) axis, which controls important functions, including sleep, response to stress, and depression. Alterations in the HPA axis appear to produce lower levels of the stress hormones norepinephrine and cortisol. (In depression, stress hormones are higher than normal.) Deficiencies produce impaired and weaker responses to psychological or physical stresses (such as infection or exercise).

The hypothalamus is a highly complex structure in the brain that regulates many important brain chemicals.

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

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Low Growth Hormone Levels. Some studies have reported low levels of insulin-like growth factor-1 (IGF, also called somatomedin C) in about a third of fibromyalgia patients. IGF is a hormone that is controlled by adult growth hormone and promotes bone and muscle growth. Low levels are associated with impaired thinking, lack of energy, muscle weakness, and intolerance to cold. Severe growth hormone deficience has been observed in a subset of fibromyalgia patients. In a 2003 study, however, researchers did not find a link between IGF levels and fibromyalgia.

Abnormal Pain Perception and Substance P. Some studies have suggested that fibromyalgia may involve overactivity in the parts of the central nervous system that process pain (called the nocioceptive system). Brain scans of fibromyalgia patients have suggested abnormalities in pain processing centers. Of particular interest is research that has detected up to three times the normal level of substance P in the cerebrospinal fluid of fibromyalgia patients. Substance P is a neurotransmitter associated with increased pain perception.

Some fibromyalgia patients may also be oversensitive to external stimulation and preoccupied with the sensation of pain. This amplification of sensation is called generalized hypervigilance. A study compared patients with fibromylagia, rheumatoid arthritis, and those without chronic pain. They were surveyed to assess their response to pain and noise. Of the three groups, the fibromyalgia patients were least tolerant of and most attentive to such stimuli. A 2001 analysis of studies on fibromyalgia, however, found no strong support for the hypervigilance theory.