PASI (Psoriasis Area and Severity Index)

The PASI is the gold-standard clinician-administered measure of psoriasis severity and extent. Developed by Fredriksson and Pettersson in 1978, it evaluates four cardinal clinical signs (erythema, induration, desquamation) across four body regions, each weighted by anatomical importance. PASI is the most widely used endpoint in psoriasis clinical trials and is endorsed by regulatory agencies (FDA, EMA) and international dermatology societies.