Lessons from fibromyalgia: abnormal pain sensitivity in knee osteoarthritis.

Fibromyalgia (FM) is a disorder that is characterized by widespread, musculoskeletal pain and abnormal pain sensitivity at multiple anatomic sites. Laboratory studies involving psychophysical and neuroimaging methods suggest that central augmentation of low intensity stimulation may contribute to abnormal pain sensitivity in FM. Recently, several investigators, using similar laboratory methods, have shown that patients with knee or hip osteoarthritis (OA) exhibit abnormal pain sensitivity or abnormal pain inhibition at anatomic sites distal to affected joints. Consistent with animal models of central sensitization, differences between patients and healthy controls in pain processing and pain inhibition at these distal sites are eliminated after nociceptive input is eliminated following total joint replacement surgery. This paper reviews these findings from our laboratory and those of independent investigators. It also presents verbal, psychophysical and neuroimaging data concerning ethnic group differences in affective and cognitive pain responses among patients with knee OA. We suggest that central sensitization as well as centrally-mediated cognitive and affective factors influence the pain responses of patients with knee OA. In addition, ethnic group differences in pain cognition and affect may contribute to differences among these groups in preferences for healthcare interventions such as total joint replacement.