Hidradenitis Suppurativa Symptom Daily Diary (HSSDD) and Questionnaire (HSSQ): Psychometric Validation and Interpretation Threshold Derivation Using Phase 3 Study Data

Introduction Hidradenitis suppurativa (HS) is a chronic inflammatory disease characterised by painful skin lesions which negatively impact patients' physical and mental wellbeing. The HS Symptom Daily Diary (HSSDD) and HS Symptom Questionnaire (HSSQ) are patient-reported outcome (PRO) tools capturing patient-perceived severity of HS symptoms. Here, we report the psychometric properties of HSSDD and HSSQ along with score interpretation thresholds. Methods Pooled data from patients with moderate to severe HS in two phase 3 studies (BE HEARD I II) were analysed. Test-retest reliability was evaluated using intraclass correlation coefficients (ICCs). Convergent validity was assessed between the HSSDD (N = 934) and HSSQ (N = 1007) compared with relevant PROs and clinician-reported outcomes (ClinROs) at baseline and Week (Wk)16. Known-groups validity was assessed, comparing HSSDD and HSSQ scores between participant subgroups pre-defined using PRO/ClinRO measures (Patient Global Impression [PGI] of HS severity, Hurley stage, International HS Severity Score System). Responsiveness was evaluated by correlating changes from baseline to Wk16 in HSSDD and HSSQ scores with changes in PGI scales. Clinically meaningful within-patient improvement thresholds were estimated using anchor- and distribution-based analyses. Symptom/impact severity thresholds were estimated using receiver operating characteristic curve analyses. Results At Wk16, HSSDD and HSSQ completion rates were 70.1% and 90.2%, respectively. Test-retest reliability analyses demonstrated good score reproducibility (ICC: HSSDD: 0.80-0.86; HSSQ: 0.73-0.82). Correlations between HSSDD and HSSQ scores and other PROs/ClinROs were generally consistent with predefined hypotheses, indicating good convergent validity. HSSDD and HSSQ scores discriminated between pre-defined subgroups, confirming known-groups validity. Sixteen-wk changes from baseline in HSSDD and HSSQ scores and anchors were moderately to strongly correlated (> 0.30), establishing responsiveness. Interpretation thresholds for both HSSDD and HSSQ were estimated. Conclusion HSSDD and HSSQ item scores demonstrated good psychometric performance in participants with moderate to severe HS. The clinically meaningful severity thresholds defined here could be used to assess treatment efficacy.