LAUSR

Well-designed clinical trials measuring valid outcomes that matter to patients 1 are pivotal in the response to the need for treatment in hidradenitis suppurativa (HS). Also known as acne inversa, this condition affects ≥ 1% of the population and may have an extreme impact on life. 2,3 The HS Core Outcome Set Collaboration (HISTORIC) has established a core outcome domain set for HS trials in a global multistakeholder process involving patients and healthcare professionals. 4 Six core domains were agreed on, including a patient and an investigator global assessment. In this issue of the BJD , Garg et al . report on the development and initial validation of an investigator global assessment (IGA) specific for HS for use in clinical intervention trials. 5 This research addresses an important gap as there was no validated HS-specific IGA available before this study. An HS physician global assessment (HS-PGA) has previously been used in trials, 6 but without thor-ough evaluation of its measurement properties. Development was done in an interactive fashion together with HS experts, methodologists and patients within HISTORIC. Multiple methods such as classification and regression trees using data from the PIONEER I randomized controlled trial (RCT) were used together with clinical input, a response defined as at least two-point improvement, in line with require-ments of the US Food and Drug Administration and responsive-ness analyses. This resulted in a six-point HS-IGA based on an objective lesion count. The score is calculated as the sum of abscesses, both inflammatory and noninflammatory nodules, and draining and nondraining fistulas in either the upper or lower body (whichever is greater). The number of lesions is then assigned to a point on the global scale: 0 = 0 – 1, 1 = 2 – 5,