According to a 1990 definition of the American College of Rheumatologists (ACR Link), a diagnosis of fibromyalgia includes:
- Widespread pain in all four quadrants for at least 3 months. This includes some axial (cervical spine, anterior chest, thoracic spine, or low back) pain.
- In addition, patients report abnormal pain sensitivity in at least 11 out of 18 possible tender points.
FM can exist by itself, but is usually accompanied by a primary or secondary chronic medical condition such as rheumatoid arthritis, hypothyroidism, and, most particularly, chronic fatigue syndrome. However, these other medical conditions are not the source of the widespread pain. Stress or lack of sleep can further increase the severity of FM symptoms. Recent research has strongly suggested the involvement of the central nervous system in the development of fibromyalgia, along with a suspected genetic predisposition.