Identification of complex regional pain syndrome in the upper limb: Skin temperature asymmetry after cold pressor test

BACKGROUND: Skin temperature asymmetry (SkTA) may assist in early identification of complex regional pain syndrome (CRPS), but previous work has been limited by methodological shortcomings including failure to account for the cutaneous nerve distribution where temperature is measured and reliance on laboratory equipment not clinically available. Pilot work suggested that a cold pressor test (CPT) provided a consistent thermoregulatory stress and might increase sensitivity/specificity of SkTA measurements generated reliably by handheld infrared (IR) thermometers. AIMS: This study investigated the sensitivity, specificity, and validity of SkTA in the upper limb to identify CRPS. METHODS: This study was part of a larger clinical trial (the SARA study: www.clinicaltrials.gov NCT02070367). Using IR thermometers, we evaluated SkTA over major peripheral nerve distributions in the hands before and after immersing a single foot in 5°C water for 30 s. Participant groups included healthy volunteers, CRPS, known nerve injury, and hand fracture. RESULTS: SkTA was measured in 65 persons, including 17 persons with CRPS (meeting Budapest criteria). Analysis of variance for n = 378 SkTA observations supported diagnosis, CPT, and nerve distribution as significant predictors (P < 0.001) explaining 94% of the variance. Post CPT, sensitivity for a >1.5°C SkTA improved to 82.4% from 58.8%, whereas specificity dropped from 56.3% to 43.8%. CONCLUSION: This study adds further support for the accuracy of SkTA as a diagnostic indicator of CRPS. Further precision in estimates will be gained from larger studies, which should also seek to replicate our findings for SkTA in the lower limbs.