Noninvasive Quantification of Cutaneous Oedema in Patch Test Reactions by Fiber Optic Near-Infrared Fourier Transform Raman Spectroscopy

Abstract

The major aim of the present study was to quantitatively differentiate various degrees of positive patch test reactions by estimating relative water content noninvasively using fiber optic near-infrared Fourier transform (NIR-FT) Raman spectroscopy. The specific intent was to examine its technical applicability and reproducibility in reading patch tests at 48 and 72 hr. Instrumental measurements at 63 patch test sites were compared visually in 19 patients with suspected allergic contact dermatitis. Raman spectra were measured in vivo in skin reacting to patches on the back using a fiber optic technique. Negative (−), doubtful (?+) and positive patch test reactions (+; ++/+++) could be separated by means of measured differences in absolute values of the 3250 cm−1 peak (ratio I3250/I2940): at 48 hr the mean increases were 0.31(−), 0.40(?+); 0.45(+); 0.69(++/+++) and at 72 hr they were 0.31(−); 0.34(?+); 0.42(+); 0.60(++/+++). At 48 hr significant differences (p<0.05) were shown between all reactions, but not between negative and doubtful reactions at 72 hr. These findings indicate that cutaneous oedema in patch test reactions can be noninvasively quantified based on positive patch test reactions by NIR-FT Raman spectroscopy, with continuous data grading of reaction intensity suitable for clinical studies at 48 and 72 hr. We also demonstrated good technical reproducibility of patch test reactions evaluation by NIR-FT Raman spectroscopy at 48 and 72 hr, showing that this method can be used to monitor the dynamics of these reactions and display the results spectroscopically.