PASI90 response: the new standard in therapeutic efficacy for psoriasis

In a non-life-threatening disease such as psoriasis, treatment goals should be referred to the improvement in severity and extent of the disease and their impact on patients' perceived health-related quality of life (HRQoL), usually measured by the Dermatology Life Quality Index (DLQI). The ultimate goal of therapy is blanching, and an improvement of 90% or better (PASI90 response) with respect to baseline Psoriasis Area and Severity Index (PASI) is considered as treatment success by the European Medicines Agency. PASI75 response has become accepted as a less stringent reasonable therapeutic goal, but absolute PASI values might provide a better benchmark, irrespective of baseline PASI. Anyway, objective measures of psoriasis involvement are clinically meaningful only if they correlate with significant improvements in DLQI, and especially with the achievement of a DLQI=0-1 status, corresponding to lack of effect of the disease on patient's HRQoL. Even though PASI75 response meets therapeutic expectations in most patients, PASI90 response or better has a significantly higher impact on DLQI improvement and is associated with significantly higher DLQI=0-1 response rates. The introduction of anti-IL17 drugs in clinical practice bears the promise of achieving PASI90 response or better in the majority of patients, and initial data suggest that the PASI90 benchmark provides better discriminatory value as regards achievement of DLQI=0-1 response. Further research is required to confirm the value of absolute PASI cut-offs as a measure of therapeutic success independent of baseline and duration of treatment, and to develop newer, more practical and more accurate measures of psoriasis severity.