Evaluation of positive patch test reactions using optical coherence tomography: A pilot study

Introduction: Patch testing is the gold standard for evaluating allergic contact dermatitis (ACD), yet current interpretation methods are limited by their subjectivity and possible variability between observers. Optical coherence tomography (OCT) imaging enables noninvasive in vivo skin visualization and holds promise as an objective method of patch test interpretation. Objective: To evaluate the micromorphological changes of patch test reactions and identify objective, quantitative OCT markers that correlate with clinically graded patch test reactions. Results: A total of 25 patch test reactions (7 grade-0, 4 grade-1+, 14 grade-2+) from 7 patients underwent OCT evaluation. Increased epidermal thickness and density was qualitatively observed in grade 1+ and grade 2+ allergic reactions while well-demarcated, signal-free cavities were observed in all grade 2+ reactions. Attenuation coefficients significantly increased across the three reaction grades (2.58 ± 0.092, 2.96 ± 0.121, 3.05 ± 0.065; P < 0.01). Cutaneous blood flow at 0.35 mm monotonically increased with reaction grade severity and blood measurements significantly differed across the three reaction grades (0.053 ± 0.011 mm/s, 0.078 ± 0.015 mm/s, and 0.121 ± 0.008 mm/s; P < 0.01). Conclusions and Relevance: Attenuation coefficient and cutaneous blood flow at 0.35 mm correlate with clinically graded patch test reactions and hold promise as objective, quantitative markers. OCT may help dermatologists differentiate clinical scoring of allergic reactions in patch test and thereby improve their diagnostic accuracy and interpretation of patch test reactions.