Differentiation of involved and uninvolved psoriatic skin from healthy skin using noninvasive visual, colorimeter and evaporimeter methods.

Abstract

Uninvolved skin of psoriasis may not be entirely normal. The object was to characterize healthy, uninvolved psoriatic skin and lesional skin by biophysical methods. Involved and uninvolved psoriatic and age-gender matched healthy skin was measured objectively with a colorimeter and evaporimeter and subjectively with visual assessment in 14 subjects. Visual assessment of erythema (E), scaling (S) and induration (I) as well as the target lesion score at the involved psoriatic skin sites were significantly elevated (p<0.05) above uninvolved psoriatic or healthy skin sites. No difference between uninvolved psoriatic and healthy skin was measured visually. Transepidermal water loss at involved psoriatic skin >uninvolved psoriatic skin >healthy skin (p<0.05). Objective assessment of skin color in 3 color scales, L*, a*, and b*, differentiated involved and uninvolved psoriatic skin from healthy skin sites. Involved psoriatic skin demonstrated higher (p<0.01) a-scale values and lower (p<0.01) L* and b* scale values than uninvolved psoriatic skin. Further, colorimeter L* and a* scale values at uninvolved psoriatic skin sites were lower and higher (p<0.05), respectively, than healthy skin. The individual chromameter parameters (L*, a*, b*) correlated well with the visual parameters (E, S and I). Composite colorimeter description (L*× b*)/a* significantly differentiated healthy skin from both involved and uninvolved psoriatic skin. These collective data highlight that even visually appearing uninvolved psoriatic skin is compromised compared with healthy skin. These objective, noninvasive but differential capabilities of the colorimeter and evaporimeter will aid in the mechanistic quantification of new psoriatic drug therapies and in conjuction with biochemical studies, add to understanding of the multifactorial pathogenesis of psoriasis.