Psoriasis Area and Severity Index (PASI)

Original Editor - User: Boluwatife Williams Top Contributors - Boluwatife Williams and Vidya Acharya

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).[1][2]

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.[1]

References[edit | edit source]

  1. 1.0 1.1 Canadian Agency for Drugs and Technologies in Health; Validity of Outcome Measures, 2018 Mar. Appendix 5
  2. 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.