Characteristic Features of Infrared Thermographic Imaging in Primary Raynaud’s Phenomenon

Abstract

Raynaud’s phenomenon (RP) is characterized by the episodic whitening of the fingers upon exposure to cold. Verification of the condition is crucial in vibration-exposed patients. The current verification method is outdated, but thermographic imaging seems promising as a diagnostic replacement. By investigating patients diagnosed with RP, the study aimed at developing a simple thermographic procedure that could be applied to future patients where verification of the diagnosis is needed. Twenty-two patients with primary RP and 58 healthy controls were examined using thermographic imaging after local cooling of the hands for 1 min in water of 10°C. A logistic regression model was fitted with the temperature curve characteristics to convey a predicted probability of having RP. The characteristics time to end temperature and baseline temperature were the most appropriate predictors of RP among those examined (p = 0.004 and p = 0.04, respectively). The area under the curve was 0.91. The cut-off level 0.46 yielded a sensitivity and specificity of 82% and 86%, respectively. The positive and negative predictive values were 69% and 93%, respectively. This newly developed thermographic method was able to distinguish between patients with RP and healthy controls and was easy to operate. Thus, the method showed great promise as a method for verification of RP in future patients. Trial registration: ClinicalTrials.gov NCT03094910.

Infrared Thermography as a Method of Verification in Raynaud’s Phenomenon

“…The control group was identical to the control group described in reference [8]. The healthy participants were recruited through advertisements in Herlev and Gentofte Hospital and in local newspapers.…”

“…The thermographic procedure, preparations, and subsequent analysis were conducted as previously described [8]. In short, the participants' hands were immersed in water of 10 • C for 60 s, and the rewarming period of the fingers was recorded using an infrared thermographic camera (FLIR SC600, FLIR ® Systems, Wilsonville, OR, USA).…”

“…In short, the participants' hands were immersed in water of 10 • C for 60 s, and the rewarming period of the fingers was recorded using an infrared thermographic camera (FLIR SC600, FLIR ® Systems, Wilsonville, OR, USA). The thermographic recordings resulted in rewarming curves, which were analyzed to obtain the seven temperature variables previously described [8]: baseline finger temperature (t base ), finger temperature immediately after cooling (t 0 ), curve type, finger temperature halfway through rewarming (t 50 ), end temperature (t end ), time to t end , and the percentage of temperature recovery at t end (R%) (R% = temperature increase/initial temperature decrease) × 100% [12]. The categorical variable curve type described the course of the temperature curve as either S-shaped or horizontal.…”

“…After the evaluation of the previously developed thermographic method, a new algorithm was generated to investigate if pRP and VWF share the same thermographic characteristics. The fitting of a new logistic prediction model based on the thermographic parameters of the patients positive for RP in the present cohort and the healthy controls and evaluation of the model were conducted as described previously [8]. All the statistical calculations were done using the statistical software R, version 4.0.2, June 2020), (R Core Team (2020).…”

“…The performances of the different methods vary widely and seem to depend on the prevalence of RP in the study population, the severity of the symptoms [4,5], and the possibility of closely controlling the environmental conditions during the examination [4,6,7]. We recently investigated infrared thermographic imaging as a method for distinguishing patients with primary Raynaud's phenomenon (pRP) from healthy individuals [8]. The study generated a prediction model that was able to predict the presence or absence of RP with a sensitivity of 82% and a negative predictive value (NPV) of 93% and was not inferior to the previous studies on thermographic imaging [5,[9][10][11].…”