Despite clinical similarities there are significant differences between acute limb trauma and complex regional pain syndrome I (CRPS I)

In order to analyze the pathophysiology behind the clinical similarity acut ely after limb trauma and in acute stages of complex regional pain syndrome (CRPS), 20 patients with external fixation after distal radius fracture (3 .5 days after surgery) without signs of CRPS and 24 patients suffering from acute CRPS I(without nerve lesion; duration, 5 weeks) were investigated. H yperalgesia to heat was tested by a feedback-controlled thermode, and to me chanical stimuli by an impact stimulator. The sympathetic nervous system wa s examined by measuring skin temperature (infra-red thermography), testing different sympathetic vasoconstrictor reflexes (laser-Doppler flowmetry) an d quantitative sudometry after thermal load (thermoregulatory sweat test). We found hyperalgesia to heat after trauma (P < 0.001), but not in CRPS, wh ereas mechanical hyperalgesia was present in both patient groups (trauma: P < 0.001; CRPS: P < 0.005). Skin temperature was significantly increased on the affected side in both patient groups (acute trauma: P < 0.001; CRPS: P < 0.005). However, sympathetic failure, as indicated by impairment of symp athetic vasoconstrictor reflexes (P < 0.02) and hyperhidrosis (P < 0.01), w as found exclusively in CRPS patients. Our results indicate that pain and v asomotor disturbances may be generated by different mechanisms acutely afte r trauma and in acute CRPS. Despite the clinical similarity, additional cha nges in the peripheral or central nervous system are required for CRPS. In the light of our observations, it seems unlikely that CRPS is a simple exag geration of post-traumatic inflammation. Copyright <(c)> 2001 International Association for the Study of Pain. Published by Elsevier Science B.V. All rights: reserved.