PASI Score

What is the PASI Score? The PASI Score, the Psoriasis Area and Severity Index, is a disease severity scale for Psoriasis that was developed through the modification of the EASI score used for atopic dermatitis. It is used to estimate the severity at a given time based on the current symptom presentation.

How is PASI scoring performed?

A. The body is divided into four parts which are divided further into the percentage of the skin affected based on a standardized measure:

1. Head and Neck: Face 33% (17% for each side), Neck 33%  (17% front and back), Scalp 33%

2. Trunk, including genitals: Front 55%, Back 45%.

3. Upper limbs: Each arm is designated as 50% with the front and back of each arm representing 25%.

4. Lower limbs: Each leg is designated 45% of the area with the front and back representing 22.5% each, and the buttocks representing 10% of the lower limb region.

These percentages are then used to score each of the four regions from 0-6, which are assigned the “AREA SCORE”.

0: No active signs of eczema

1: 1-9% affected

2: 10-29% affected

3: 30-49% affected

4: 50-69% affected

5: 70-89% affected

6: 90-100% affected

B. The PASI is based on three signs of psoriasis:

  • Erythema
  • Induration
  • Desquamation 

The severity of each sign is measured as a scale of 0-4, as absent, mild, moderate, severe, and very severe.

This severity measure of each sign is added for each body region to get the “SEVERITY SCORE”.

C. The regions are scored by multiplying the severity score, the area score, and the multiplier that represents the body surface area:

Head/Neck: 0.1 (if 7 years of age or less: 0.2)

Trunk: 0.3

Upper Limb: 0.2

Lower Limb: 0.4 (if 7 years of age of less: 0.3)

D. The Final PASI score is calculating the four region scores, and can range from 0 to 72, and a score of 5-10 is considered moderate disease, and over 10 is considered severe. In clinical trials, the PASI score is used to rate the response to treatment, so a PASI 75 would indicate a 75% decrease in symptoms from baseline, and is the current benchmark for approval from the FDA.

Source: Clinical Review Report: Guselkumab (Tremfya): (Janssen Inc.): Indication: For the treatment of adult patients with moderate-to-severe plaque psoriasis who are candidates for systemic therapy or phototherapy [Internet]. Ottawa (ON): Canadian Agency for Drugs and Technologies in Health; 2018 Mar. Appendix 5, Validity of Outcome Measures. Available from: