Psoriasis Area and Severity Index (PASI)

PASI Calculator

Head (10% BSA)

Area Involved (Head)

Erythema (Head)

Induration (Head)

Desquamation (Head)

Upper Extremities (20% BSA)

Area Involved (Upper)

Erythema (Upper)

Induration (Upper)

Desquamation (Upper)

Trunk (30% BSA)

Area Involved (Trunk)

Erythema (Trunk)

Induration (Trunk)

Desquamation (Trunk)

Lower Extremities (40% BSA)

Area Involved (Lower)

Erythema (Lower)

Induration (Lower)

Desquamation (Lower)

Total PASI Score: –

Score: 0.0

Default 0 for unset items.

Quantifies severity of psoriasis.

Why Use

May be used to track disease progression and help guide treatment (e.g. retinoids). In some countries (e.g. Australia), PASI is used to determine eligibility for government-subsidized prescription drugs. Used in clinical trials of therapies to treat psoriasis.

When to Use

Patients with psoriasis. Use with caution in patients with smaller areas of involvement, as the score is less sensitive in those cases.

Formula

Total PASI = addition of PASI for each body region (i.e., head/neck, upper limbs, trunk, and lower limbs) PASI for each body region = lesion severity x percentage of area affected x body surface area, defined as below Lesion severity for each body region = erythema + induration/thickness + desquamation/scaling, defined as below Lesion characteristic (separately scored for head/neck, upper limbs, trunk, and lower limbs) Points Erythema None 0 Slight 1 Moderate 2 Severe 3 Very severe 4 Induration/thickness None 0 Slight 1 Moderate 2 Severe 3 Very severe 4 Desquamation/scaling None 0 Slight 1 Moderate 2 Severe 3 Very severe 4 Percentage of area affected*: Percentage of area affected Points 0% 0 1-9% 1 10-29% 2 30-49% 3 50-69% 4 70-89% 5 90-100% 6 *Validated using palm method of body surface area estimation (patient’s palm, excluding fingers, roughly correlates to 1% BSA). Body surface area: Region Constants Head/neck 0.1 Upper limbs 0.2 Trunk 0.3 Lower limbs 0.4

Pearls / Pitfalls

Initially developed to assess treatment efficacy of retinoids. PASI is the most widely used psoriasis clinical severity score. Validated using palm method of body surface area estimation (patient’s palm, excluding fingers, roughly correlates to 1% BSA ). PASI is neither a linear nor normally distributed score, as it is less sensitive at lower end of scale, and accurate PASI assessment requires some level of clinical gestalt in assigning points. PASI is limited by lack of interrater and intrarater reliability, and lack of utility in detecting change in mild psoriasis. Calculating the PASI can be error-prone if not done systematically.

Management

When measured serially: T he term “PASI 75” indicates a 75% reduction (improvement) in PASI, and is generally considered a “good response” to therapy. PASI 50 to 74 is considered partial response, and PASI <50 is considered treatment failure. Patients with PASI 75 can likely continue current management, and those with PASI <50 can be considered for more aggressive treatment such as with biologics.

Critical Actions

Consultation with a dermatologist is warranted in patients with psoriasis. PASI assessments become more reliable with experience in scoring.

Advice

Higher PASI scores indicate more severe psoriasis and therefore likely warrant more aggressive treatment. May be trended over time to assess treatment efficacy.

More Information

Interpretation: Higher PASI scores indicate higher severity of psoriasis. Scores range from 0 (no disease) to 72 (maximal disease severity).