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Calculate the Psoriasis Area and Severity Index (PASI) score to quantify disease severity and track treatment response over time.
0=None, 1=Slight, 2=Moderate, 3=Severe, 4=Very severe
Thickness/elevation of plaques
Amount of scaling present
Percentage of region affected
0=None, 1=Slight, 2=Moderate, 3=Severe, 4=Very severe
Thickness/elevation of plaques
Amount of scaling present
Percentage of region affected
0=None, 1=Slight, 2=Moderate, 3=Severe, 4=Very severe
Thickness/elevation of plaques
Amount of scaling present
Percentage of region affected
0=None, 1=Slight, 2=Moderate, 3=Severe, 4=Very severe
Thickness/elevation of plaques
Amount of scaling present
Percentage of region affected
The Psoriasis Area and Severity Index (PASI) is the most widely used tool for measuring the severity of psoriasis. It combines assessment of lesion severity (erythema, induration, and scaling) with the area of skin involved.
For each region: (Erythema + Induration + Scaling) × Area Score × Regional Weight
Total PASI = Sum of all four regional scores (maximum 72)
PASI is commonly used to evaluate treatment efficacy in clinical trials and practice. Key benchmarks include PASI 75 (75% improvement from baseline), PASI 90 (90% improvement), and PASI 100 (complete clearance). Many biologic therapies aim for PASI 90 or higher.
A PASI score below 5 indicates mild psoriasis. However, "good" is relative - for someone starting with severe disease (PASI >20), achieving PASI <10 represents significant improvement. The goal is typically PASI ≤3 or complete clearance (PASI 0).
PASI 75 means a 75% reduction in PASI score from baseline. For example, if baseline PASI was 20, achieving PASI 75 means the current score is 5 or lower. This is considered a good treatment response in clinical trials.
PASI scoring requires practice and training for accuracy. It involves subjective assessment of lesion characteristics and area estimation. Inter-rater variability can occur, which is why standardized training and photography documentation are helpful for tracking changes over time.
PASI should be calculated at baseline before starting treatment and during follow-up visits to monitor response. Typical intervals are every 12-16 weeks when initiating new systemic therapy, then every 3-6 months once stable.
No, PASI is purely a clinical assessment of physical disease severity and extent. It doesn't capture impact on quality of life, which should be assessed separately using tools like the Dermatology Life Quality Index (DLQI). Both measures together provide a comprehensive view.
PASI is primarily designed for chronic plaque psoriasis. It may be less suitable for other forms like pustular psoriasis, erythrodermic psoriasis, or primarily nail/scalp involvement. Alternative assessment tools may be needed for these variants.
Treatment is typically considered inadequate if PASI 50 (50% improvement) is not achieved after an appropriate trial period, or if disease worsens after initial response. Many guidelines now aim for PASI 75 or better as the treatment goal.
The regional weights in PASI reflect anatomical proportions of body surface area. The lower limbs (legs) represent approximately 40% of total body surface area, which is why they have the highest weight (0.4) in the calculation.
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