• •Assessing psoriasis severity in clinical research or practice.
• •Specifically designed to precisely reflect the status of limited disease (< 10% body surface area involvement).
• •Documenting treatment success and determining eligibility for biologics or targeted therapies (e.g., Roflumilast).

• •Not intended for patients with purely inverse, erythrodermic, or pustular psoriasis without classic plaques.

Total mPASI = Σ (Region Weight × Lesion Severity × Area Score)

• •Erythema (E) + Induration (T) + Desquamation (S).
• •Graded as: 0 (None), 1 (Slight), 2 (Moderate), 3 (Severe), 4 (Very Severe).

Unlike standard PASI which uses categorical scores (e.g., 1 for 1-9%), mPASI uses the actual percentage involved (Actual% / 10) for values under 10%. For example, 1% involvement = 0.1, 5% = 0.5. This prevents the floor effect where a patient with 1% and 9% involvement previously received the same area score of 1.

• •PASI 75 (75% improvement from baseline) is widely accepted as clinically meaningful improvement in trials, though PASI 90 and PASI 100 are increasingly used for highly effective biologics.
• •The standard PASI suffers from a lack of sensitivity in mild disease when using categorical area scoring (1-6). The modified PASI (mPASI) corrects this, making it highly valuable for evaluating treatments targeted at mild-to-moderate disease (e.g., topical roflumilast or tapinarof).
• •Accuracy and inter-rater reliability improve significantly with clinician experience.

• •0: No disease (Clear). Maintain current regimen.
• •PASI 50/75/90: Calculate the percentage reduction from baseline. If a patient fails to achieve at least a PASI 50 with topical therapies, escalate to phototherapy or systemic therapy.
• •Maximal disease severity (72): Indicates severe, extensive disease requiring immediate systemic/biologic intervention.

The original PASI was developed in 1978 by Fredriksson and Pettersson to evaluate a new oral retinoid. The modified PASI (mPASI) evolved later as trial endpoints shifted toward mild-to-moderate disease, necessitating a continuous area scale for <10% BSA involvement to provide adequate statistical sensitivity.