Causes:

The most common type is primary fibromyalgia, in which the causes are not known. Many experts believe that fibromyalgia is not a disease, but rather a chronic pain condition brought on by several abnormal body responses to stress. Physical injuries, emotional trauma, or viral infections such as Epstein-Barr may be triggers of the disorder, but none have proven to be a cause of primary fibromyalgia.

Research published in the December 2006 issue of Current Pain and Headache Reports found that the areas in the brain that are responsible for the sensation of pain are different in fibromyalgia patients from the same areas in healthy people.

People with fibromyalgia have been found to have decreased activity in opioid receptors in parts of the brain that affect mood and the emotional aspect of pain. This reduced response might explain why fibromyalgia patients are likely to havedepression, and are less responsive to opioid painkillers, researchers say.

Chronic Sleep Disturbance

Sleep disturbances are common in fibromyalgia. Both adult and young patients with fibromyalgia have a higher-than-average rate of a sleep disorder called periodic limb movement disorder (PLMD). PLMD used to be called nocturnal myoclonus. Patients with PLMD involuntarily contract their leg muscles every 20 - 40 seconds during sleep. This may occasionally wake up the patient.

Some researchers believe that fibromyalgia does not lead to poor sleeping patterns, but that sleep disturbances come first. Researchers continue to investigate the link between fibromyalgia and sleep.

• In one study, healthy volunteers reported fibromyalgia-like pain after they had been subjected to disrupted deep sleep. Disturbed sleep appears to trigger factors in the immune system that cause inflammation, pain, fatigue, and lower tolerance to pain. A 2004 study found that patients with fibromyalgia have increased rates of cyclic alternating sleep pattern (CAP). Increased CAP produced serious sleep problems, which were strongly linked to symptom severity. Previous studies have also suggested that CAP may be related to PLMD.
• A 2004 report found that sleep disorders that cause breathing problems are common in women with fibromyalgia.
• Other biological measures of troubled sleep, however, such as levels of the hormone melatonin, which helps regulate circadian rhythms and the sleep-wake cycle, appear to be normal in most people with fibromyalgia.

Brain Chemicals and Hormonal Abnormalities

Many abnormalities of hormonal, metabolic, and brain chemical activity have been described in studies of fibromyalgia patients. Changes appear to occur in several brain chemicals, although no regular pattern has emerged that fits most patients. Since there has been no clear cause-and-effect relationship established, this may be a result of the effects of pain and stress on the central nervous system, and 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.)

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

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. Studies suggest that changes in growth hormone likely stem from the hypothalamus in the brain. While researchers did not find a link between IGF-1 levels and fibromyalgia, a 2005 study indicated that serum growth hormone levels may be a marker of the disorder.

Abnormal Pain Perception and Substance P. Some studies have suggested that fibromyalgia may involve too much activity in the parts of the central nervous system that process pain (the nociceptive system). Brain scans of fibromyalgia patients have suggested abnormalities in pain processing centers. For example, researchers have detected up to three times the normal level of substance P in the cerebrospinal fluid of fibromyalgia patients. Substance P, a chemical messenger of the nervous system, is associated with increased pain perception.

Some fibromyalgia patients may also be oversensitive to external stimulation, and overly anxious about the sensation of pain. This increase in awareness is called generalized hypervigilance. One study compared patients with fibromyalgia or rheumatoid arthritis to those without chronic pain. Researchers then measured the different groups' responses to pain and noise. Of the three groups, the fibromyalgia patients were least tolerant, and most aware, of such stimuli. However, one analysis of studies on fibromyalgia found no strong support for the hypervigilance theory.

A conflict between sensory perception and nervous system processing might occur in people with fibromyalgia. Fibromyalgia patients have been found to have greater awareness of, or less tolerance for, movement problems (such as tremor) that don't match with their expected sensory feedback. This mismatch in sensory signals might enhance the perception of pain.

Immune Abnormalities

Fibromyalgia has symptoms that resemble those of some rheumatic illnesses, including rheumatoid arthritis and lupus (systemic lupus erythematosus). These are autoimmune diseases in which a defective immune system mistakenly attacks the body's own healthy tissue, producing inflammation and damage. The pain in fibromyalgia, however, does not appear to be due to autoimmune factors, and there is little evidence to support a role for an inflammatory response in fibromyalgia.

Psychological and Social Effects

Although not primary causes, psychological and social factors may contribute to fibromyalgia in three ways:

• They could make individuals susceptible to fibromyalgia.
• They may play some role in triggering the onset of the condition.
• They may perpetuate, or be responsible for, the condition.

Studies have reported a greater number of severe experiences of emotional and physical abuse in patients with fibromyalgia, compared with the general population. Most often, the abuse came from family members or partners. This suggests that post-traumatic stress disorder (PTSD) or chronic stress may play a strong role in the development of fibromyalgia in some patients. PTSD, an anxiety disorder, is a reaction to a specific traumatic event. Symptoms of this condition, which can last for years after the traumatic event, include emotional withdrawal, hopelessness, irritability, mood swings, sleep problems, inability to concentrate, and an excessive startle response to noise. Some evidence indicates that PTSD actually results in changes in the brain, possibly from long-term over-exposure to stress hormones.

Muscle Abnormalities

Some research found muscle abnormalities in fibromyalgia patients. These problems can be classified as the following:

• Biochemical abnormalities: For example, one study reported that fibromyalgia patients had lower levels of the muscle-cell chemicals phosphocreatine and adenosine triphosphate (ATP). Such chemicals regulate the level of calcium in muscle cells. Calcium is an important component in the muscles' ability to contract and relax. If ATP levels are low, calcium is not "pushed back" into the cells, and the muscle remains contracted.
• Functional abnormalities: The pain and stress of the disease itself may harm muscle function.
• Structural and blood flow abnormalities: Some researchers saw overly thickened capillaries (tiny blood vessels) in the muscles of fibromyalgia patients. The abnormal capillaries could produce lower levels of compounds essential for muscle function, as well as reduce the flow of oxygen-rich blood to the muscles.

To date, none of these abnormalities have a clearly defined relationship with fibromyalgia.