BACKGROUND:
Differentiation between irritant and allergic skin reactions in epicutaneous patch testing is based largely on subjective clinical criteria, with the risk of high intra- and interobserver variability. Novel dermatological imaging using optoacoustic mesoscopy allows quantitative three-dimensional assessment of microvascular biomarkers.
METHODS:
We investigated the potential of optoacoustic imaging to improve the precision of patch test evaluation by examining 69 test reactions and 48 healthy skin sections in 52 patients with suspected type-IV-allergy.
RESULTS:
We identified biomarkers from the optoacoustic images. Allergic reactions were associated with higher fragmentation of skin vasculature than irritant reactions (19.5±9.7 vs. 14.3±3.7 fragments/100 pixels2 ; P≤.01), as well as lower ratio of low- to-high-frequency acoustic signals (1.6 ±0.5 vs. 2.0±0.6, P≤.0045). Allergic reactions graded “++” showed higher vessel fragmentation than reactions graded “+” (25.4±13.2 vs. 17.1±6.5 fragments/100 pixels2 ; P≤.0074). A linear model combining the biomarkers fragmentation and frequency ratio could differentiate allergic from irritant test reactions with an area under the receiving operator characteristic curve of 0.80 (95% CI 0.64-0.91), reaching a sensitivity of 81% and specificity of 63%.
CONCLUSIONS:
Optoacoustic mesoscopy shows potential to help in differentiating allergic and irritant test reactions based on novel biomarkers that may reflect vasodilation, vessel tortuosity and edema.

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