Mechanistic and clinical aspects of complex regional pain syndrome (CRPS).

Complex regional pain syndromes (CRPS, reflex sympathetic dystrophy, causalgia) are painful disorders that develop after trauma affecting a limb with (I) or without (II) nerve injury. Clinical features are pain, impairment of motor function, swelling and autonomic abnormalities (changes in sweating and blood flow). Autonomic abnormalities. The maximal skin temperature difference between the affected and unaffected extremity that occurs during a controlled thermoregulation can be used as a diagnostic tool. SMP. Sympathetic outflow to the painful extremity was experimentally activated. The intensity as well as area of spontaneous pain and mechanical hyperalgesia increased considerably in patients that had been classified as having SMP by positive sympathetic blocks. A pathological interaction between sympathetic vasoconstrictor and afferent neurons within the affected skin is the likely explanation for SMP in CRPS patients. Motor abnormalities. Kinematic analysis of target reaching as well as grip force analysis showed a pathological sensorimotor integration located in the parietal cortex. Furthermore, MEG studies demonstrated a continuous inhibition of the primary motor cortex. Neurogenic inflammation. Some features of acute CRPS (vasodilatation, swelling, pain) indicate a localized inflammatory process. Transcutaneous electrical stimulation of nociceptive C-fibre provoked protein extravasation into the interstitial fluid (microdialysis) only in CRPS patients and not in controls.