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

J Dermatolog Treat. 2015 Feb;26(1):23-31. doi: 10.3109/09546634.2013.865009. Epub 2013 Dec 20.


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.

Keywords: IL-17; Investigator’s Global Assessment; Physician’s Global Assessment; Psoriasis Area and Severity Index; secukinumab.

Publication types

  • Review

MeSH terms

  • Antibodies, Monoclonal / therapeutic use*
  • Antibodies, Monoclonal, Humanized
  • Biological Products / therapeutic use
  • Humans
  • Psoriasis / drug therapy*
  • Psoriasis / pathology
  • Severity of Illness Index*


  • Antibodies, Monoclonal
  • Antibodies, Monoclonal, Humanized
  • Biological Products
  • secukinumab