1. What is the PASI Score?

Definition: The Psoriasis Area and Severity Index (PASI) is a tool used to measure the severity and extent of psoriasis.

Purpose: It helps dermatologists assess disease severity and monitor treatment effectiveness.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• E — Erythema (redness) severity (0-4 scale)
• I — Induration (thickness) severity (0-4 scale)
• D — Desquamation (scaling) severity (0-4 scale)
• A — Area affected (0-6 scale)
• Subscripts H (head), U (upper limbs), T (trunk), L (lower limbs)

3. Interpretation of PASI Scores

Score Ranges:

• 0 = No psoriasis
• <5 = Mild psoriasis
• 5-10 = Moderate psoriasis
• >10 = Severe psoriasis
• >40 = Very severe psoriasis

4. Using the Calculator

Tips: For each body region, assess and enter:

• Erythema (0-4): 0=none, 1=slight, 2=moderate, 3=marked, 4=very marked
• Induration (0-4): Same scale as erythema
• Desquamation (0-4): Same scale as erythema
• Area (0-6): 0=0%, 1=<10%, 2=10-29%, 3=30-49%, 4=50-69%, 5=70-89%, 6=90-100%

5. Frequently Asked Questions (FAQ)

Q1: Why are different weights used for body regions?
A: The weights (0.1-0.4) account for the relative surface area of each body region.

Q2: How often should PASI be calculated?
A: Typically at diagnosis and then every 3-6 months during treatment.

Q3: What is PASI 75/90/100?
A: These refer to 75%/90%/100% improvement from baseline PASI score, common treatment goals.

Q4: Are there limitations to PASI?
A: Yes, it doesn't assess quality of life impact and can be subjective in scoring.

Q5: What's considered a clinically significant improvement?
A: A reduction of ≥50% in PASI score (PASI 50) is typically considered meaningful.