Psychometric Validation and Meaningful Change Thresholds of the New Nasal Polyposis Symptom Diary

Abstract

Objectives: The Nasal Polyposis Symptom Diary (NPSD) is a novel and short patient-reported outcome (PRO) tool specifically developed to assess important and relevant symptoms reported by patients with chronic rhinosinusitis with nasal polyposis (CRSwNP). We evaluated the psychometric properties of 4 predefined NPSD-derived scores intended to support symptom-improvement assessments of investigational therapies for inclusion in product labeling. Methods: Five hundred eighteen patients with severe CRSwNP from a Phase III clinical trial (NCT03401229) completed the NPSD, comprising 11 items: 8 symptom-specific, 2 symptom-impact, and 1 optional medication-compliance. The psychometric characteristics of 3 single-item symptom scores (Nasal Blockage Score [NBS], Nasal Congestion Score [NCS], and Difficulty with Sense of Smell Score [DSS]) and a Total Symptom Score (TSS, summary of the 8 symptom-specific items) were evaluated for reliability, validity, and ability to detect change. Within-patient meaningful change thresholds (MCTs) were established using anchor- and distribution-based methods. Comparative PROs included the 22-item Sino-Nasal Outcome Test (SNOT-22) and Patient Global Impression of Severity (PGI-S). Results: The TSS exhibited strong internal consistency (Cronbach α = .88) and test-retest reliability (intraclass correlation coefficient >.80). Correlation between the TSS and SNOT-22 total score indicated good convergent validity ( r = .70). All 4 NPSD scores demonstrated known-groups validity (significant differences among subgroups of patients with predetermined disease severity levels based on PGI-S categories) and were sensitive to detect change in patients’ clinical status (significant differences among subgroups of patients with reported changes between 2 time-points in PGI-S and Patient Global Impression of Change scores). MCTs for improvement were established at 1.0 point for NBS, NCS, and DSS, and 4.0 points for TSS. Conclusion: These findings support the reliability, validity, and suitability of the 4 NPSD-derived scores for evaluating treatment effect on CRSwNP symptoms and their use in clinical trials with predetermined MCTs for improvement.