Estimation of Health Utility Values for Eosinophilic Granulomatosis With Polyangiitis

Eosinophilic granulomatosis with polyangiitis (EGPA) is a rare autoimmune disease, characterised by inflammation of small- to medium-sized blood vessels, however, it remains poorly described in the literature. The purpose of this study was to characterise EGPA health states and to estimate utility weights for each to inform economic evaluations. To achieve this, we aimed to characterise and develop health-state vignettes representing EGPA and to estimate utility values from the United Kingdom (UK) public and individuals from the UK with EGPA.

Vignettes were developed using evidence from a literature review and patient-reported outcomes (PRO) data. Qualitative interviews with patients (n = 7), clinicians (n = 4), and one health-related quality of life (HRQoL) expert were conducted to refine the content of the vignettes. To derive utility values, vignettes were assessed using an online survey by members of the UK public (N = 316) and patients with EGPA (N = 20). Participants evaluated each vignette by imagining themselves in the described vignettes and completed the EQ-5D-5L for each vignette.

Based on the literature review and PRO data from a clinical trial and real-world study, four health-state vignettes for EGPA were defined: remission, relapse, non-refractory, and refractory, which clinicians recognised as clinically meaningful. These vignettes captured the physical, psychological, and functional impacts of EGPA across health states. The subsequent survey was completed by 316 members of the UK public, and 20 patients with EGPA. Utility scores for remission (public: 0.675; patients: 0.690) scored highest, followed by non-refractory (public: 0.619; patients: 0.621), relapse (public: 0.453; patients: 0.410), and refractory (public: 0.151; patients: 0.059). EGPA patients' scores were largely consistent with those of the public, except for the refractory state, where patients reported lower scores.

The findings highlight the substantial HRQoL impact of EGPA across all health states, with a higher perceived impact for the relapse and refractory health states. The public and EGPA patient samples produced consistent ratings. This study addresses an evidence gap by characterising health states in EGPA and defining the HRQoL of patients with EGPA across these health states. Multiple evidence sources were integrated to develop these values, which we believe represents a robust approach to estimating health state utilities in a rare disease.