Evidence for abnormal pain processing in fibromyalgia syndrome.

OBJECTIVE: To review the pathophysiology of fibromyalgia syndrome.
DESIGN: Review of the literature available on Medline (1965-2001).
RESULTS: Fibromyalgia syndrome is a chronic pain syndrome that predominantly afflicts women. It is characterized by widespread pain, insomnia, fatigue, and the presence of multiple tender points. Despite intensifying research, the etiology of fibromyalgia has remained unclear. Importantly, neither infections, trauma, nor psychiatric abnormalities consistently precede the onset of pain in patients with this syndrome. There is, however, mounting evidence for central pain processing abnormalities in almost all fibromyalgia patients. These anomalies include hyperalgesia, allodynia, abnormal temporal summation of second pain, neuroendocrine abnormalities, and abnormal activation of pain-related brain regions.
CONCLUSIONS: Multiple abnormal findings in fibromyalgia patients strongly indicate a neuropathic pain syndrome, reminiscent of complex regional pain syndrome or postherpetic neuralgia. In addition, fibromyalgia syndrome seems to share similar characteristics with these neuropathic pain syndromes, including ineffective response to many analgesics.