Skin temperature side differences--a diagnostic tool for CRPS?

Complex regional pain syndrome type I (CRPS I) is a chronic painful disease of one extremity that may develop as a disproportionate consequence of a trauma affecting the limbs without overt nerve injury. It is clinically characterized by sensory, motor and autonomic symptoms including vascular abnormalities. Previously, we have reported that pathophysiological alterations of the ongoing sympathetic activity play a crucial role in vasomotor disturbances (Brain 124 (2001) 587). As a companion article, the aim of this study was to evaluate the diagnostic value of skin temperature side differences in consideration of the spontaneous sympathetic vasoconstrictor activity. Twenty-five patients with CRPS I were studied. Fifteen patients with painful limbs of other origin and 20 healthy individuals served as controls. Controlled thermoregulation was performed to change cutaneous sympathetic vasoconstrictor activity by the use of a thermal suit: skin sympathetic vasoconstrictor neurones were activated by whole-body cooling and nerve activity was abolished by whole-body warming. Skin temperature at the affected and unaffected limbs (infra-red thermometry) was measured under resting conditions and continuously monitored during controlled modulation of sympathetic activity. The results showed only minor skin temperature asymmetries between both limbs under resting conditions in most CRPS patients. However, during controlled thermoregulation temperature differences between both sides increased dynamically and were most prominent at a high to medium level of vasoconstrictor activity. In both control groups, there were only minor side differences in temperature both in rest and during thermoregulatory changes of sympathetic activity. When comparing the diagnostic value of skin temperature asymmetries in CRPS I, sensitivity was only 32% under resting conditions, but increased up to 76% during controlled alteration of sympathetic activity. Specificity was 100% at rest and 93% at controlled thermoregulation. We concluded that the degree of unilateral vascular disturbances in CRPS I depends critically on spontaneous sympathetic activity. Taking this into consideration, skin temperature differences in the distal limbs are capable of reliably distinguishing CRPS I from other extremity pain syndromes with high sensitivity and specificity.