Thermography of hand rewarming parameters in Raynaud’s phenomenon

This study aimed to investigate the use thermography of rewarming hands (a) for individuals without a clinical diagnosis for circulatory issues, evaluating the distal dorsal difference (DDD) and the absolute temperature after cold stress; (b) to evaluate individuals which have been previously diagnosed with primary and secondary Raynaud’s phenomenon (RP); and (c) to indicate parameters (most suitable finger and trial period) to support the RP diagnostic with thermography. We evaluated 174 individuals, 150 without specific diagnosis and 24 participants with RP. A thermal camera was used to record skin temperature following a cold stress protocol. The hands were then immersed up to the carpal level in a container with cold water. Images were recorded immediately after the emersion and every 5 min, until 20 min post-immersion. For the data analysis, normalized histograms were mapped to define the probability density function of absolute temperature and DDD. The best finger and the best analysis time were defined by the ratio between variance and chi-square, to find the best trade-off between model fitting and data separation into two distinct groups. A hit rate (recall value) of 91.7% for the DDD model and 79.2% for the absolute temperature model were found using DDD ≥  − 1.0 °C for the ring finger and T ≥ 25.5 °C for the index finger. Results show that DDD and absolute temperature models could be suitable as a RP condition exclusion criterion. Moreover, the use of multiple fingers is recommended. We recommend using at least 15 min for the rewarming analysis period to maximize the thermal differences and the inspection using the ring finger (if the metric is the DDD) and the index finger (if the used metric is the absolute temperature).