Exaggeration of tissue trauma induces signs and symptoms of acute CRPS I, however displays distinct differences to experimental CRPS II

As CRPS I frequently develops after tissue trauma, we proposed that an exaggerated inflammatory response to tissue trauma may underlie CRPS I. Therefore, we studied the vascular inflammatory, nociceptive and apoptotic sequelae of (i) soft tissue trauma and (ii) exaggerated soft tissue trauma in comparison to those of (iii) sciatic nerve chronic constriction injury, modeling CRPS II. Standardized soft tissue trauma (TR) was induced by means of a controlled impact injury technique in the hind limb of pentobarbital-anesthetized rats. Additional animals received soft tissue trauma and femoral arterial infusion of mediator-enriched supernatant achieved by homogenization and centrifugation of traumatized muscle tissue in order to provoke an exaggerated trauma response (ETR). Infusion of supernatant of non-traumatized muscle served as control intervention (STR, sham trauma response). Neuropathy was induced by chronic constriction injury of the sciatic nerve (CCI). Untreated animals served as controls (CO). Detailed nociceptive testing showed temporarily decreased mechanical pain thresholds in ETR animals that resolved within 14 days, while TR and STR animals, i.e. those with singular limb trauma, and controls remained free of pain. Neither cold- nor heat-evoked allodynia developed in post-traumatic animals, whereas CCI animals presented the well-known pattern of ongoing neuropathic pain. Using high-resolution in vivo multifluorescence microscopy, muscle tissue of traumatized animals revealed an enhanced inflammatory response that was found most pronounced in ETR animals. CCI of the sciatic nerve was not accompanied by tissue inflammation; however, induced myocyte apoptosis. Collectively, these data indicate that exaggeration of trauma response induces signs and symptoms of acute CRPS I. Pain perception displays differences to that in CRPS II. Apoptosis turns out to be a distinctive marker for CRPS, warranting further evaluation in clinical studies.