[CENTRALIZED PAIN AND FIBROMYALGIA: WHAT DO WE MEAN WHEN WE SAY "IT'S ALL IN YOUR HEAD"?]

Fibromyalgia is a syndrome characterized by chronic widespread musculoskeletal pain, tenderness, fatigue and associated symptoms which include cognitive difficulties, abdominal symptoms etc. A leading paradigm regarding the pathogenesis of fibromyalgia (and similar functional disorders) focuses on the concept of central sensitization. This concept describes a situation in which there is an increased sensitivity of the central nervous system to the processing and transmission of pain, leading to the development of clinical phenomena such as allodynia and hyperalgesia. Various lines of evidence have contributed to the development of the central sensitization paradigm. A decrease in the capacity of the nervous system to perform descending pain inhibition is one aspect of this paradigm. Increased windup and long term potentiation are additional phenomena. An increase in the CSF-level of pain-facilitating neurotransmitters, coupled with a decrease in pain inhibitory transmitters, has also been described. Novel mechanisms such as microglia cell activation are under investigation. Certain clinical characteristics may alert the clinician to the possibility that a patient is suffering from centralized pain (i.e. fibromyalgia or related syndromes). Multiple sites of pain are typical, as well as a long history of pain- related complaints in the same patients. Disturbed sleep, fatigue and dyscognition are typical. Various triggers such as physical trauma, infection and stress are often reported and tenderness is demonstrable on physical examination. Functional imaging of the central nervous system, including techniques such as fMRI, proton magnetic resonance spectroscopy and resting connectivity analysis, are improving our understanding regarding the neural mechanism underlying central sensitization.