PASI is a combined assessment of lesion severity and affected area into a single score. PASI scores can range from a lower value of 0, corresponding to no signs of psoriasis, up to a maximum of 72.0. The body is divided into 4 areas for scoring (head, arms, trunk, legs); each area is scored by itself and scores are combined for final PASI. For each area, percent of skin involved is estimated: 0 (0%) to 6 (90-100%), and severity is estimated by clinical signs, erythema, induration and desquamation; scale 0 (none) to 4 (maximum). Final PASI = sum of severity parameters for each area multiplied by the area score weight of section (head: 0.1, arms: 0.2 body: 0.3 legs: 0.4). A PASI 100 response corresponds to complete clearing of psoriasis (PASI = 0).