While there is a lot of ongoing speculation about what triggers fibromyalgia, its causes have yet to be definitively identified and confirmed. Recent research has generally found that fibromyalgia is most likely a result of what scientists call central sensitization, or unusual responses in the nervous system with regard to pain perception.

Fibromyalgia's Biochemical Triggers
"The [current] consensus is that fibromyalgia is not a problem with the muscles, joints, or tendons, but rather a problem with the central nervous system," says Dr. Bruce Solitar, clinical associate professor of medicine in the division of rheumatology at NYU Medical Center/Hospital for Joint Diseases in New York. While it's easy to think that pain felt by someone who has experienced no physical damage to the body might be categorized as purely psychosomatic, the sensations that a fibromyalgia patient experiences are as real as any other pain.

This was clearly demonstrated when researchers did MRI imaging of patients with fibromyalgia. When they pressed on certain areas of the participants' bodies, they found dramatically increased activity in the pain center of the brain. One theory attributes this phenomenon to an increased release of Substance P, the chemical that activates nerves when there is a painful stimulus. "In fibromyalgia patients, Substance P is being released even in the absence of a painful stimulus. And there seems to be an amplified release when there is a painful stimulus," explains Dr. Solitar. In addition, the brain's regulatory effect, which sends "down signals" to turn off pain, also appears to be abnormal in people with fibromyalgia — so when a painful stimulus does occur, it gets amplified rather than dampened.

Fibromyalgia's Physical and Emotional Triggers
So what causes the nervous system to malfunction in such a way? Scientists aren't sure, but a number of conditions have been linked to the development of fibromyalgia. These include:

Infection. The Epstein-Barr virus, influenza, and hepatitis B and C have all been implicated in the development of fibromyalgia. "These viruses may have [long-term] effects on the immune system. It's also possible that viral particles attach to glial cells, which are cells within the brain that affect neurotransmission [and influence the pain response]," says Dr. Solitar. Additionally, there is a well-established connection between Lyme disease and fibromyalgia: Some patients who have been treated for Lyme — and ostensibly recover from it — continue to experience the unusually high frequency of unprovoked pain that characterizes fibromyalgia.

Trauma. Sometimes the development of fibromyalgia is linked to physical injury, especially in the upper spinal region. In other cases, it's associated with great emotional stress, like the death of a family member or the loss of a job. The possible link between these unrelated types of trauma is the neurohormonal change that both physical injury and emotional stress can trigger. Psychological processes can change — and can be changed by — alterations in the function of hormone-regulating centers like the hypothalamus and the pituitary and adrenal glands, which in turn affect the nervous system.

Fibromyalgia's Other Common Threads
"Fibromyalgia has been associated with all age groups, though women between the ages of 30 and 50 have a higher incidence of the disease," says Dr. Solitar. While this increased prevalence among younger females suggests a hormonal connection, he says it's also possible that it's related to diagnosis. "Women tend to [naturally] be more tender [or sensitive to pain] than men, so if you base your diagnosis on tender points, you're likely to diagnose more women with fibromyalgia than men."

Genes. Found in approximately 2 percent of the U.S. population (3.4 percent of women and 0.5 percent of men), fibromyalgia often develops in multiple members of the same families, although it's not clear if this is the result of genetic or environmental effects. "Family members of people with fibromyalgia seem to be more tender than others," says Dr. Solitar, "but there isn't a lot of conclusive genetic research out there."

Still a mystery. In many cases, why fibromyalgia strikes is still largely unknown. "For a lot of patients, we don't come up with a good explanation for the development of fibromyalgia," Dr. Solitar notes. "We all get exposed to stress regularly. And while trauma and infections do seem to be a common [fibromyalgia] theme, there are a lot of people who just slowly develop a sense of feeling poorly."