Comparative Analysis of Temperature Variations Following Sympathetic Blocks in Warm and Cold Subtypes of Complex Regional Pain Syndrome (CRPS): A Retrospective Cohort Study

<b>Background/Objectives</b>: The pathophysiological mechanisms of temperature asymmetry differ between patients with warm and cold subtypes of Complex Regional Pain Syndrome (CRPS). Consequently, the response to lumbar sympathetic blocks (LSBs) and the resulting temperature improvement may vary between these two subtypes. We aimed to evaluate whether there was a significant difference in temperature elevation following sympathetic blocks in warm versus cold subtypes of CRPS. <b>Methods</b>: We calculated the temperature difference by analyzing forward-looking infrared (FLIR) thermal camera images of the affected extremity at pre-block and 5-min post-block time points. The primary outcome measure was that the mean temperature increase following LSB would be higher in the cold CRPS group than in the warm CRPS group. The secondary outcome measure was that the mean temperature elevation following the sympathetic block in the cold CRPS subtype would be at least 50% higher than in the warm CRPS subtype. <b>Results</b>: The study assessed warm and cold CRPS subtypes by analyzing temperature profiles from 90 lumbar sympathetic blocks performed on 34 patients. The temperature change in the affected extremity following LSB varied widely, with the highest increase observed in one patient at 10.99 °C. The cold CRPS patients demonstrated a higher mean temperature increase at the 5 min time point following LSB, averaging 3.37 °C in initial cases and 2.67 °C across all cases. In comparison, warm CRPS patients had lower mean increases of 0.58 °C in initial cases and 1.23 °C across all cases. Notably, the mean temperature rise in the cold CRPS group exceeded that of the warm CRPS group by more than 50%, meeting the secondary outcome goal. <b>Conclusions</b>: Our results indicated that patients with the cold subtype of CRPS tend to experience greater temperature improvements compared to those with the warm subtype after undergoing a sympathetic block. Therefore, our findings suggest that the criteria for determining the success of a sympathetic block should be revised to account for the cold and warm subtypes of CRPS.