The 5-point Investigator's Global Assessment (IGA) Scale: A modified tool for evaluating plaque psoriasis severity in clinical trials

Background: To evaluate new psoriasis treatments, clinicians, regulators and pharmaceutical developers require well-accepted, clinically meaningful measures of disease severity. The Psoriasis Area and Severity Index (PASI) score is most widely used as a primary endpoint in clinical trials, although it is not routinely used in clinical practice. Objective: Characterize a 5-point Investigator's Global Assessment (IGA) tool and evaluate whether it meets the needs for a valid, clinically meaningful measure. Methods: A 5-point IGA tool was developed with input from regulatory authorities and clinical trial investigators involved with psoriasis drug development and evaluation. Associations between IGA 0/1 responder rates and PASI scores were evaluated using data from two phase 2 studies with the anti-interleukin (IL)-17A monoclonal antibody secukinumab (AIN457) that utilized a similar 6-point IGA. Results: The 5-point IGA has a more stringent definition for a score of 1 ("almost clear'') compared with 6-point IGA/Physician's Global Assessment (PGA) tools used in previous trials of other biologics in moderate-to-severe psoriasis. Whereas IGA/PGA 0/1 responder rates for earlier scales are strongly associated with PASI 75, the IGA 0/1 rate for the secukinumab 6-point scale was more robust, demonstrating a strong association with PASI 90, and the results for the 5-point IGA are expected to show the same association. Discussion: The 5-point IGA is a valid measure of disease severity and meets the need for a clinically meaningful measure of success for psoriasis treatment studies.