Psoriasis Area and Severity Index (PASI)
Description[edit | edit source]
The Psoriasis Area and Severity Index (PASI) is a tool that measures and scores the severity of psoriatic lesions as well as the patient's response to therapy. The PASI is the most frequently used system and is a widely used instrument in psoriasis trials. It combines the assessment of the severity of psoriasis lesions and the area affected into a single score, typically ranging from 0 (indicating no disease) to 72 (indicating maximal disease severity).
How PASI score is assessed[edit | edit source]
To assess the severity of psoriasis using the Psoriasis Area and Severity Index (PASI), the body is divided into four regions: the head (h), upper extremities (u), trunk (t), and lower extremities (l), with each region representing a specific percentage of the total body surface area (BSA). These regions account for 10%, 20%, 30%, and 40% of the total BSA, respectively.
For each of these anatomical regions, healthcare providers assess the severity of psoriasis independently for erythema (redness), induration (thickness), and scaling (flaking) using a scale that ranges from 0 (indicating no symptoms) to 4 (indicating very severe symptoms).
- Induration: This refers to the thickness or hardening of the psoriatic lesions.
- Erythema: This assesses the redness or inflammation associated with the psoriatic plaques.
- Scaling: This evaluates the extent of scaling or flaking of the skin affected by psoriasis.
The degree of psoriatic involvement in each region is classified into the following categories:
0 = No involvement
1 = Involvement of 1% to 9% of the region
2 = Involvement of 10% to 29%
3 = Involvement of 30% to 49%
4 = Involvement of 50% to 69%
5 = Involvement of 70% to 89%
6 = Involvement of 90% to 100%
The PASI score is calculated using the following formula:
PASI = (0.1 * (Eh + Ih + Sh) * Ah) + (0.2 * (Eu + Iu + Su) * Au) + (0.3 * (Et + It + St) * At) + (0.4 * (El + Il + Sl) * Al)
In this formula, E represents erythema, I represents induration, S represents scaling, A represents the area, h corresponds to the head score, u to the upper extremities score, t to the trunk score, and l to the lower extremities score. This formula combines the individual scores for each region and aspect to provide an overall PASI score, which is a numerical representation of the severity of psoriasis.
References[edit | edit source]
- Canadian Agency for Drugs and Technologies in Health; Validity of Outcome Measures, 2018 Mar. Appendix 5
- Bożek A, Reich A. The reliability of three psoriasis assessment tools: Psoriasis area and severity index, body surface area and physician global assessment. Advances in Clinical and Experimental Medicine. 2017;26(5):851-6.