Investigating the clinical implication of corneometer and mexameter readings towards objective, efficient evaluation of psoriasis vulgaris severity

Abstract

In clinical settings, although Psoriasis Area and Severity Index (PASI) scoring system can provide a quick visual assessment of the severity of psoriasis vulgaris, there is still a strong demand for higher efficiency and accuracy in quantifying the inflammation status of psoriatic lesions. Currently, there are already commercial systems, such as the Courage + Khazaka Corneometer and Mexameter that measure skin capacitance and optical reflectance, for conveniently quantifying the status of skin barrier function and erythema of skin. Despite numerous comparisons of the Courage + Khazaka system with the PASI scoring system, they are rarely compared on parity with diffuse reflectance spectroscopy (DRS) based systems. In this study, we employed a custom-built DRS system shown to be able to determine the skin water-protein binding status and the hemoglobin concentration, and we performed cross-validation of the DRS measurement results with the readings derived from the Corneometer and Mexameter as well as a portion of the PASI scores. Our results revealed that the erythema readings from the Mexameter were a good representation of skin oxygenated hemoglobin but not the deoxygenated hemoglobin. On the other hand, the dermatologists recruited in this study were inclined to rate higher scores on the "erythema" category as skin's deoxygenated hemoglobin level was higher. Thus, the Mexameter derived erythema readings may not be coherent with the PASI erythema scores. Further, the Corneometer derived skin capacitance readings were well correlated to the PASI "desquamation" and "thickness" scores, while the PASI "desquamation" evaluation was a dominating factor contributing to the DRS deduced water-protein binding status. We conclude that the DRS method could be a valuable addition to existing skin capacitance/reflectance measurement systems and the PASI scoring system toward achieving a more efficient and objective clinical psoriasis vulgaris severity evaluation.

Conflict of interest statement

The authors declare no competing interests.

© 2022. The Author(s).

Figures

Figure 1

Correlation plots of the pure water fitting residuals at the first water absorption overtone obtained from the DRS system and the Corneometer hydration readings for (a) the psoriatic lesion sites and (b) their adjacent normal sites. The r values indicate the Pearson correlation coefficients. Shaded domain represents 95% confidence band. A p-value greater than 0.05 represents that the fitted model is not significantly different from the model y = constant (no correlation).

Figure 2

Values of total hemoglobin and erythema scores at the psoriatic lesion and uninvolved sites of 15 subjects obtained from DRS and Mexameter.

Figure 3

Correlation plots for total hemoglobin values and erythema scores collected from the DRS and Mexameter, respectively, at (a) psoriatic lesion and at (b) adjacent uninvolved skin. Shaded domain represents 95% confidence band. A p-value greater than 0.05 represents that the fitted model is not significantly different from the model y = constant (no correlation).

Figure 4

Correlation plots for the oxygenated and deoxygenated hemoglobin values and erythema scores obtained from DRS and Mexameter, respectively, at (a,c) psoriatic lesion, and at (b,d) adjacent uninvolved skin. Shaded domain represents 95% confidence band. A p-value greater than 0.05 represents that the fitted model is not significantly different from the model y = constant (no correlation).

Figure 5

Schematic of the DRS system. Two optical switches were used in the system where one was used for switching light source to one of the two source fibers, and the other was used to switch the collected light signal to one of the two spectrometers. The fiber setup of the optical probe is shown in the inset.