Increased neural sympathetic activation in fibromyalgia syndrome.

Fibromyalgia (FM) is a syndrome characterized by widespread musculoskeletal pain, although the mechanisms underlying the pain have not been fully elucidated. FM patients describe a number of nonspecific symptoms, such as anxiety, depression, fatigue, unrefreshing sleep, and gastrointestinal complaints, which appear after a flu-like illness, or after physical or emotional trauma in half of the patients, and are often exacerbated by exertion, stress, lack of sleep, and weather changes. There may also be symptoms of orthostatic intolerance, which suggests underlying abnormalities in cardiovascular neural regulation. Research suggests that various components of the central nervous system are involved, including the hypothalamic-pituitary-adrenal (HPA) axis, pain-processing pathways, and the autonomic nervous system (ANS). This review discusses the general aspects of the altered HPA and ANS, sympathetic overactivity, and alterations in cardiovascular autonomic responses to gravitational stimuli.