Quantitative sensory studies in complex regional pain syndrome type 1/RSD

Objective: Patients with complex regional pain syndrome type 1 (CRPSD1) may have thermal allodynia after application of a non-noxious thermal stimulus to the affected limb. We measured the warm, cold, heat-evoked pain thresho ld and the cold-evoked pain threshold in the affected area of 16 control pa tients and patients with complex regional pain syndrome type 1/RSD to test the hypothesis that allodynia results from an abnormality in sensory physio logy. Setting: A contact thermode was used to apply a constant 1 degreesC/second increasing (warm and heat-evoked pain) or decreasing (cold and cold-evoked pain) thermal stimulus until the patient pressed the response button to sho w that a temperature change was felt by the patient. Student t test was use d to compare thresholds in patients and control patients. Results: The cold-evoked pain threshold in patients with CRPSD1/RSD (p <0.0 01) was significantly decreased when compared with the thresholds in contro l patients (i.e., a smaller decrease in temperature was necessary to elicit cold-pain in patients with CRPSD1/RSD than in control patients). The heat- evoked pain threshold in patients with CRPS1/RSD was (p <0.05) decreased si gnificantly when compared with thresholds in control patients. The warm- an d cold-detection thresholds in patients with CRPS1/RSD were similar to the thresholds in control patients. Conclusions: This study suggests that thermal allodynia in patients with CR PS1/RSD results from decreased cold-evoked and heat-evoked pain thresholds. The thermal pain thresholds are reset (decreased) so that non noxious ther mal stimuli an perceived to be pain (allodynia).