Patient Journey, Treatment Patterns, and Disease Burden of Patients With Idiopathic Hypereosinophilic Syndrome.

Introduction: Idiopathic hypereosinophilic syndrome (I-HES) is a rare disorder characterized by persistent eosinophilia without an identifiable underlying cause, leading to organ damage and dysfunction. The objectives of this study were to describe the real-world demographics, patient journey, treatment patterns, and disease burden of patients with I-HES. Methods: Data were drawn from the Adelphi Real World HES Disease Specific Programme, a cross-sectional survey of physicians and their patients with I-HES in Europe (France, Germany, Italy, Spain, and the UK) and the United States from July to December 2023. Results: The overall population included 117 physicians and 451 patients. Patients were predominately male (62%), White (87%), and the mean (standard deviation [SD]) age was 44.7 (16.1) years. Mean (SD) and median (range) time between symptom onset and I-HES diagnosis was 8.2 (11.1) and 4.2 (0-87.3) months, respectively. Most patients (66%) were treated with corticosteroids, and the mean (SD) and median (range) doses of oral and/or parenteral corticosteroids were 19.1 (20.3) and 10.0 (1.0-100.0) mg/day, respectively. The use of interleukin-5/receptor alpha targeted therapies was low (23%). Patients had a mean (SD) of 7.7 (6.4) symptoms at diagnosis; 58% had organ system damage attributed to I-HES, and disease was perceived by physicians as moderate or severe in 72%. Patient-reported health-related quality of life, work productivity, and fatigue were negatively impacted in patients with deteriorating or moderate-to-severe disease. Conclusion: These findings underscore the need for greater disease awareness to support timely diagnosis with use of targeted, corticosteroid-sparing treatments to improve patient outcomes. Trial Registration: The authors have confirmed clinical trial registration is not needed for this submission.