Prefrontal cortical hyperactivity in patients with sympathetically mediated chronic pain

Chronic pain continues to impose a large burden of suffering, yet its neura l correlates remain poorly understood. In sympathetically mediated chronic pain (SMP), peripheral sympathetic blockade temporarily relieves this pain, so that related neural activity can be studied without perturbing sensory inputs. We used functional magnetic resonance imaging and thermal painful s timuli applied to the chronically painful body site, before and after sympa thetic blockade, to examine the cortical network of chronic pain. The chron ic SMP state was associated with a widely spread prefrontal hyperactivity, increased anterior cingulate activity and decreased activity in the thalamu s contralateral to the body side suffering from SMP, but was unrelated to s ensorimotor activity. Ineffective sympathetic blocks, i.e. blocks that did not diminish the SMP pain, did not change the cortical responses to the pai nful thermal stimulus; while effective placebo resulted in similar response s to those of effective blocks. These findings provide evidence for abnorma l brain responses to pain in patients with chronic SMP, which engages prefr ontal/limbic networks more extensively than in acute pain-states. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.