Justification of objectification of MED in the lesion focus in psoriasis

Background: As a rule, the starting dose for phototherapy of dermatoses is determined depending on the minimum erythemic dose (MED). MED is determined subjectively by visual assessment of the severity of erythema after preliminary UV irradiation. This method does not allow an objective assessment of the starting dose, and also cannot be considered completely safe, since exposure to the skin with significant doses of UFOs can lead to skin damage. The use of noninvasive optical diagnostic methods allows us to obtain data on pathological and physiological processes in both healthy skin and pathologically altered tissues, allowing us to objectively assess the MED in areas of healthy skin and its equivalent within the lesionThe aim of the study was to determine differences in the optical characteristics of the skin, in the lesions of vulgar psoriasis and in the contralateral intact areas of the skin. Methods: A prospective, observational study with the participation of 12 volunteers with psoriasis, who evaluated the optical properties of the "psoriatic plaque" in comparison with the contralateral area of healthy skin (methods of absorption spectroscopy, optical coherence tomography and diffuse reflection spectroscopy). The study was carried out using the LACK-M diagnostic complex and the Multicom device, an optical coherence tomograph, and a video capillaroscope. The data were statistically processed using the Wilcoxon criterion and Spearman's rank correlation coefficient. The critical significance level is p=0.05.Results: The method of diffuse reflection spectroscopy showed statically significant differences between intact and affected skin - in 10 out of 12 patients, psoriasis-affected skin was characterized by greater reflectivity than intact skin. There were also differences in the determination of the melanin index and volumetric blood filling. There is evidence that the melanin index can be considered as a more accurate criterion of sensitivity of the psoriasis focus to UFOS compared to the skin phototype. The thickness of the epidermis of the plaque and the volume of blood filling of tissues within it turned out to be higher than in areas of intact skin of contralateral localization. Conclusion: According to the results of the study, we assume that the MED in the area of the unaffected skin area and in the lesion in vulgar psoriasis will differ and the value of the MED in the lesion can be predicted noninvasively and safely by optical diagnostic methods.