Psoriasis Area and Severity Index
Measures psoriasis severity by affected area and lesion intensity.
When to use
Adults with psoriasis, to quantify severity and track treatment response.
Pearls and pitfalls
- PASI combines affected area and intensity of erythema, induration and desquamation across four regions.
- Head, trunk, upper limbs and lower limbs have different weights in the calculation.
- The index is useful in trials and follow-up but does not capture quality of life or joints.
- The assessment is subjective and should be made by the same observer when possible.
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Formula
PASI = 0.1 × head + 0.3 × trunk + 0.2 × upper limbs + 0.4 × lower limbs, each region multiplied by the sum of erythema, induration and desquamation and by area.
Evidence
Classic index to measure psoriasis severity and treatment response in research and specialty practice.
References
- Fredriksson T, Pettersson U. Severe psoriasis: oral therapy with a new retinoid. Dermatologica. 1978;157(4):238-244. doi:10.1159/000250839
Frequently asked questions
What is Psoriasis Area and Severity Index?
Measures psoriasis severity by affected area and lesion intensity. Adults with psoriasis, to quantify severity and track treatment response.
How is the result calculated?
PASI = 0.1 × head + 0.3 × trunk + 0.2 × upper limbs + 0.4 × lower limbs, each region multiplied by the sum of erythema, induration and desquamation and by area.
How should the result be interpreted?
Classic index to measure psoriasis severity and treatment response in research and specialty practice.
What are the sources?
Fredriksson T, Pettersson U. Severe psoriasis: oral therapy with a new retinoid. Dermatologica. 1978;157(4):238-244.