The possibility of objectifying the determination of the minimum erythemic dose in the lesion in vulgar psoriasis

BACKGROUND: Currently, the starting dose for phototherapy of various dermatoses is determined depending on the minimum erythemal dose. Minimum erythemal dose is determined subjectively by a doctor's visual assessment of the severity of erythema after preliminary irradiation with ultraviolet radiation in various doses, taking into account the Fitzpatrick skin phototype (I–VI). This method does not allow for an objective assessment of the starting dose. The use of non-invasive optical diagnostics of the skin allows obtaining data on pathological and physiological processes both in healthy skin and in pathologically altered tissues, allowing for an objective assessment of minimum erythemal dose in areas of healthy skin and its equivalent within the lesion. AIM: To determine the differences in the optical characteristics of the skin, established using non-invasive optical diagnostic methods in the lesions of vulgar psoriasis and in the contralateral intact areas of the skin. MATERIALS AND METHODS: A prospective, observational study involving 12 volunteers (4 women and 8 men) with psoriasis, who underwent an assessment of the optical properties of a "psoriatic plaque" in comparison with a contralateral area of healthy skin, using optical diagnostic methods (absorption spectroscopy, optical coherence tomography and diffuse reflectance spectroscopy). RESULTS: Statistically significant differences between intact and affected skin were demonstrated by the diffuse reflection spectroscopic method. Differences in the determination of the melanin index and volumetric blood filling were also revealed. Data were obtained indicating that the melanin index can be considered as a more accurate criterion for the sensitivity of a psoriasis lesion to UFO compared to the skin phototype. The thickness of the plaque epidermis and the volume of blood filling of the tissues within it were higher than in areas of intact skin of the contralateral localization. CONCLUSION: Based on the results of the study, we assume that the minimum erythemal dose in the area of the unaffected skin and in the lesion in vulgar psoriasis will differ and the minimum erythemal dose value in the lesion can be predicted non-invasively and safely using optical diagnostic methods.