Studies of hormonal, metabolic, and brain chemical activity in FM patients have shown a number of abnormalities. Brain scans of FM patients have revealed reduced blood flow to certain regions of the brain related to pain sensation. Of particular interest to researchers are possible abnormalities in the brain system known as the hypothalamus-pituitary-adrenal gland axis, which controls important functions, including growth, sleep, response to stress, and depression. One research target is the hormone somatomedin C (also called insulin-like growth factor), which is produced by the pituitary gland in the brain during deep sleep and is responsible for communicating information about pain-producing stimuli to the brain. Very high levels of somatomedin C have been detected in the spinal fluid of FM patients. Such increased levels may cause a heightened sensitivity for pain in such patients, who can experience pain even after mild muscular activity. This causes patients to reduce their physical activity, which, in turn, results in muscle weakness, leading to a perpetual loop of muscle atrophy, and increasing pain with less and less physical exertion. The pain also causes on-going sleep disturbance. Excess somatomedin C may be due to a genetic defect or may be derived from early unhealthy sleep habits that, over time, cause hormonal and brain chemical imbalances.
People with FM also tend to have low levels of the neurotransmitter serotonin and its precursor, an amino acid called tryptophan. (A neurotransmitter is a chemical in the brain that serves as a messenger between neurons.) Low levels of both these chemicals are associated with depression and other symptoms of FM, including gastrointestinal distress, migraine headaches, and anxiety. Some experts believe that migraine headaches and FM are related because of possible defects in the systems that regulate serotonin and another neurotransmitter, epinephrine (commonly called adrenaline). Low levels of magnesium have also been noted in both FM and migraine sufferers.