Table 1

Elements of the Psoriasis Area and Severity Index (PASI)*

*Steps in generating PASI score
(a) Divide body into four areas: head, arms, trunk to groin, and legs to top of buttocks.
(b) Generate an average score for the erythema, thickness, and scale for each of the 4 areas (0 = clear; 1–4 = increasing severity)†.
(c) Sum scores of erythema, thickness, and scale for each area.
(d) Generate a percentage for skin covered with psoriasis for each area and convert that to a 0–6 scale (0 = 0%; 1 = <10%; 2 = 10–<30%; 3 = 30–<50%; 4 = 50–<70%; 5 = 70–<90%; 6 = 90–100%).
(e) Multiply score of item (c) above times item (d) above for each area and multiply that by 0.1, 0.2, 0.3, and 0.4 for head, arms, trunk, and legs, respectively.
(f) Add these scores to get the PASI score.
†Erythema, induration and scale are measured on a 0–4 scale (none, slight, mild, moderate, severe)
Area scoring criteria (score: % involvement)
0: 0 (clear)
1: <10%
2: 10–<30%
3: 30–<50%
4: 50–<70%
5: 70–<90%
6: 90–<100%
1Redness†
2Thickness†
3Scale†
4Sum of rows 1, 2, and 3
5Area score‡
6Score of row 4×row 5×the area multiplierrow 4×row 5×0.1row 4×row 5×0.2row 4×row 5×0.3row 4×row 5×0.4
7 Sum row 6 for each column for PASI score