Fibromyalgia Cause No clear cause for fibromyalgia exists. There are theories as to what may cause it, but little evidence is available to support them. Since fibromyalgia is a syndrome of many symptoms, it has been difficult to find a specific cause for the combined symptoms. Some theories suggest that fibromyalgia. May be linked to an imbalance in brain chemicals that control mood and can also cause an unrestful sleep cycle. This leads to fatigue and a lowered tolerance for pain, which in turn leads to tender points and widespread pain in the muscles and soft tissues. Once this occurs, a person becomes less physically active, and the muscles and tissues become more sensitive and painful and more easily injured or irritated. May be due to an imbalance of hormones released by the pituitary gland, which can cause fatigue, water retention, and muscle and joint pain. May be associated with nerve cells in the spinal cord and brain, which can be more sensitive to pain in people who develop fibromyalgia. This may occur from changes in chemicals in the brain or spinal cord that regulate pain. As a result, the person senses pain more easily, and widespread muscle pain occurs. May be caused by below-normal levels of growth hormone in their bodies. Growth hormone deficiency has been associated with low energy, muscle weakness, sensitivity to cold, weakened ability to remember and think, and other problems. Regardless of what causes it, fibromyalgia seems to involve a cycle of increased sensitivity to pain and decreased physical activity. Increasing pain makes a person less physically active. Muscles that are not exercised regularly are more likely to be injured during activity. It is also possible that people with fibromyalgia are more sensitive to pain or have muscles that are more easily irritated or injured. The irritated or injured muscles are painful. Some doctors think the muscles of people with fibromyalgia remain sore because they do not repair themselves as well as the muscles of people who do not have this syndrome. Muscle pain, sometimes occurring together with disrupted sleep and daytime fatigue, leads to less and less activity.