Objective outcome measures of systemic sclerosis (SSc)-related Raynaud's phenomenon(RP) are badly needed. Our objectives were to (a) further validate thermographic response to a standard hand cold challenge as an outcome measure by assessing sensitivity to change and (b) explore mobile phone thermography as a feasible, ambulatory tool.
Twelve patients with a SSc-spectrum disorder admitted for intravenous iloprost infusions underwent a standard cold challenge before and after one infusion. Thermographic measurements included area under the rewarming curve (AUC) and maximum rewarming temperature (MAX). Before and during another infusion, each patient underwent monitoring of finger skin temperature by two methods: continuous thermocouple recording (the standard method) and mobile phone thermography.
All cold challenge summary measures (including AUC and MAX) increased after iloprost (most not significantly). However, when the response curves were modelled after averaging across fingers (linear mixed models, three versions), significant change was detected. For example, with Model 1 (no interaction between period and time) temperature was on average 1.67 (95% CI 1.49 to 1.85, p<0.001)OC higher post-iloprost.
Mobile phone and thermocouple temperature measurements showed a strong estimated latent correlation (0.88 [95% CI 0.81 to 0.92]). The estimated increases/hour were 0.25 (95% CI 0.05 to 0.45)OC for the thermocouple and 0.36 (0.13 to 0.60)OC for mobile phone thermography.
Our pilot study suggests that (a) thermographic response to a cold challenge is sensitive to change and (b) mobile phone thermography could bring feasibility to thermographic parameters as outcome measures in later phase, large-scale, community-based clinical trials of RP.