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

ABSTRACT

BACKGROUND: Hidradenitis suppurativa (HS) is a chronic inflammatory disease. The HS core outcome set calls for a patient global assessment (PtGA). OBJECTIVES: 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 patients with HS in Denmark and the USA. A cross-sectional observational study was done with adults with HS in the USA and Denmark. Candidate PtGA item, demographic items and multiple patient-reported scales - the Hidradenitis Suppurativa Quality of Life (HiSQOL), Dermatology Life Quality Index (DLQI) and numerical rating scale (NRS) for pain - were concurrently administered to evaluate convergent and known-groups validity. Scales with a single-item assessment of change were readministered 24-72 h 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 by significant correlations with HiSQOL score [r = 0·79, 95% confidence interval (CI) 0·75-0·82] and DLQI (r = 0·78, 95% CI 0·74-0·82). The PtGA displayed known-groups validity with DLQI score bands based on significance of an anova (P < 0·001). Good test-retest reliability was supported by the intraclass correlation coefficient (0·82, 95% CI 0·78-0·85) for those who reported stable HS. Responsiveness was assessed by differences in PtGA score against a patient-reported assessment of change, which showed significant differences towards improvement. CONCLUSIONS: The single-item PtGA exhibits reliability, validity and responsiveness in assessing HS-specific HRQoL in HS, making it a good provisional tool for HS clinical research.