Histologic grading system for psoriasis vulgaris.

BACKGROUND: Psoriasis vulgaris is a disease of substantial clinical and microscopic diversity and the histologic diagnosis depends upon an aggregate of histologic criteria, some characteristic of psoriasis and others shared with other dermatoses. While involved in drug testing with micromolar concentrations of active agents on small psoriatic plaques, this grading system was developed to quantify as objectively as possible the degree of psoriatic change present at the time of biopsy.
METHODS: Using established references of dermatopathology and a review of the pertinent literature, the salient histologic features of psoriasis were listed and assigned value scores from 1 to 3. The highest score was given to those microscopic criteria most characteristic of the disease. The cumulative score of all features present then gives a mathematical score for each biopsy.
CONCLUSIONS: This paper presents an uncomplicated mathematically weighted system of grading biopsy specimens from a disease process that shows a spectrum of microscopic features, but is often not diagnostic. The schema offers a method of grading change that can be especially important in studies of therapeutic agents.