Objective measurements of erythema, elasticity and scale could overcome the inter- and intra-observer variations of subjective evaluations for psoriasis severity.

Background: Most conventional subjective assessments for psoriasis have inevitable inter- and intra-observer variations. Objective: We investigated the objective bioengineering parameters of color and mechanical properties which are possible substitutes of the erythema, scale, and thickness scores of psoriatic plaque. Methods: Age, gender, and Psoriasis Severity Index (PSI) were noted. In addition, bioengineering parameters of color, mechanical properties, and scale were obtained. Results: The most prominently correlated bioengineering parameters were hue (tan(-1) b*/a*), desquamation index (DI), and elasticity (R7) for PSI erythema, scale, and thickness, respectively. These parameters not only showed significant differences between lesion and control groups but also changed according to psoriasis severity scores. We also showed that brighter, scaly lesions had lower elasticity while the more erythemic lesions corresponded to a more fluid-like state. Conclusion: We found that three bioengineering parameters are potential candidates for an objective Psoriasis Severity Index (oPSI).