Reliable and objective outcome measures to facilitate clinical trials of novel treatments for systemic sclerosis (SS c)–related Raynaud's phenomenon (RP ) are badly needed. Laser speckle contrast imaging (LSCI ) and thermography are noninvasive measures of perfusion that have shown excellent potential. This multicenter study was undertaken to determine the reliability and validity of a hand cold challenge protocol using LSCI , standard thermography, and low‐cost cell phone/mobile phone thermography (henceforth referred to as mobile thermography) in patients with SS c‐related RP .
Patients with RP secondary to SS c were recruited from 6 UK tertiary care centers. The patients underwent cold challenge on 2 consecutive days. Changes in cutaneous blood flow/skin temperature at each visit were imaged simultaneously using LSCI , standard thermography, and mobile thermography. Measurements included area under the curve (AUC ) for reperfusion/rewarming and maximum blood flow rate/skin temperature after rewarming (MAX ). Test–retest reliability was assessed using intraclass correlation coefficients (ICC s). Estimated latent correlations (estimated from multilevel models, taking values between −1 and 1; denoted as rho values) were used to assess the convergent validity of LSCI and thermography.
In total, 159 patients (77% with limited cutaneous SS c) were recruited (84% female, median age 63.3 years). LSCI and standard thermography both had substantial reliability, with ICC s for the reperfusion/rewarming AUC of 0.67 (95% confidence interval [95% CI ] 0.54, 0.76) and 0.68 (95% CI 0.58, 0.80), respectively, and ICC s for the MAX of 0.64 (95% CI 0.52, 0.75) and 0.72 (95% CI 0.64, 0.81), respectively. Very high latent correlations were present for the AUC s of LSCI and thermography (ρ = 0.94; 95% CI 0.87, 1.00) and for the AUC s of standard and mobile thermography (ρ = 0.98; 95% CI 0.94, 1.00).
This is the first multicenter study to examine the reliability and validity of cold challenge using LSCI and thermography in patients with SS c‐related RP . LSCI and thermography both demonstrated good potential as outcome measures. LSCI , standard thermography, and mobile thermography had very high convergent validity.