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Background Traditional metrics for evaluating the severity of psoriasis are subjective, which complicates efforts to measure effective treatments in clinical trials. Methods We collected images of psoriasis plaques and calibrated the coloration of the images according to an included color card. Features were extracted from the images and used to train a linear discriminant analysis classifier with cross-validation to automatically classify the degree of erythema. The results were tested against numerical scores obtained by a panel of dermatologists using a standard rating system. Results Quantitative measures of erythema based on the digital color images showed good agreement with subjective assessment of erythema severity (κ = 0.4203). The color calibration process improved the agreement from κ = 0.2364 to κ = 0.4203. Conclusion We propose a method for the objective measurement of the psoriasis severity parameter of erythema and show that the calibration process improved the results.

Birt-Hogg-Dube syndrome (BHD) is an uncommon autosomal dominant genodermatosis characterized by fibrofolliculomas and trichodiscomas on the face and neck with acrochordons in flexural areas. These skin signs serve as markers for internal disease, most importantly spontaneous pneumothoraces and renal cancers. BHD is caused by a mutation in a tumor suppressor gene. This gene encodes the protein folliculin (FLCN), important for normal functioning of the mammalian target of rapamycin (mTOR) signaling pathway.1