Fibromyalgia (FM) is a painful, noninflammatory condition characterized by a history of widespread pain, and diffuse tenderness on examination. Although FM is defined on the basis of pain and tenderness, most individuals with FM also display a number of nondefining symptoms, including fatigue, sleep disturbances, headaches, or memory difficulties.

Chronic musculoskeletal pain can result from a central non-nociceptive mechanism such as in FM, from peripheral nociceptive mechanisms such as in mechanical osteoarthritis (OA) or in inflammatory rheumatoid arthritis (RA), or from neuropathic pain mechanisms such as in diabetic neuropathy.

FM tender points are discrete regions of the body where a 4-kg pressure is applied with digital palpation, and if the individual experiences pain when this area is pushed, it is considered a “positive” tender point. Even when this definition was originally adopted, it was stated that these criteria were not meant to be strictly applied in clinical practice. Only about half of the patients seen in clinical practice who clearly present with FM will meet these strict criteria; many individuals have pain that is more limited in distribution, or have fewer than 11 tender points.

The precise cause for FM remains unclear. There have been numerous studies suggesting that there is a strong familial aggregation of FM, although no studies have differentiated whether this is due to hereditary or shared environmental influences.

It is also clear that there are a number of environmental “stressors”, including physical trauma, infections, autoimmune disorders, endocrine conditions, and emotional stress, that seem to be capable of “triggering” the development of FM.

There have been several types of physiologic abnormalities that have been identified in individuals with FM and related conditions that may help explain the basis of symptoms. The hallmark of FM appears to be a central disturbance in pain processing that is largely unexplained by psychological factors. The evidence for this comes from numerous studies employing various types of experimental pain testing paradigms, as well as from objective abnormalities of neurotransmitters (e.g., substance P) in the cerebrospinal fluid of patients with FM.

Most recently, functional imaging studies have confirmed that when patients with FM are given a low-pressure stimulus (that would not be felt as painful by a control subject), they not only experience pain, but also have activations in the pain-processing regions of the brain, again confirming augmented central processing of pressure, heat, and other stimuli. There have also been a number of abnormalities in both neuroendocrine and autonomic function that have been identified in subgroups of patients with FM.

Although the dualistic notion that any illness is either “organic” or “functional” should be abandoned, because of the realization that all illnesses likely have a biological basis, this debate still continues with respect to FM and other related conditions. It is likely that in many individuals this illness begins as primarily a neurobiological problem, and in some individuals never progresses past this point because of appropriate treatment, good coping skills, and adequate support systems. But in other individuals,
with chronicity of symptoms, concurrent psychological, psychiatric, and behavioral factors either develop or become more prominent.