Validation of global item for assessing impact on quality of life of patients with hidradenitis suppurativa*

BACKGROUND: Hidradenitis suppurativa (HS) is a chronic inflammatory disease that is not well understood. The HS core outcome set calls for a patient global assessment (PtGA), for which measures are limited. OBJECTIVES: Our aim is to assess the validity, reliability, and responsiveness of a candidate single-item PtGA for HS-specific health-related quality of life (HRQOL). METHODS: Cognitive debriefing interviews were conducted with HS patients in Denmark (DK) and the United States (US). Field testing was conducted via a cross-sectional observational study with adults with HS in the US and DK. The candidate PtGA item, demographic items, and multiple patient-reported scales including the Hidradenitis Suppurativa Quality of Life (HiSQOL), Dermatology Life Quality Index (DLQI), numerical rating scale (NRS) for pain were concurrently administered to evaluate convergent and known-groups validity. The scales with a single-item assessment of change were administered again 24-72 hours later to evaluate reliability and responsiveness. RESULTS: After cognitive debriefing, the candidate PtGA for HS-specific HRQOL was finalized with five response levels. Convergent validity of the PtGA was supported with significant correlations with the HiSQOL score r = 0.79 [95CI: 0.75-0.82] and DLQI (r = 0.78, [95CI: 0.74-0.82]). The PtGA displayed known-groups validity with the DLQI score bands based on significance of an analysis of variance (p