The minimal important difference of the epistaxis severity score in hereditary hemorrhagic telangiectasia

Objectives/Hypothesis Hereditary hemorrhagic telangiectasia (HHT) is a disease of abnormal angiogenesis, causing epistaxis in over 96% of patients. The Epistaxis Severity Score (ESS) was developed as a standardized measurement of nasal symptoms among HHT patients. The minimal important difference (MID) of a disease index estimates the smallest change that a patient and clinician would identify as important. This study aims to establish the MID of the ESS in a diverse population of HHT patients. Study Design Retrospective cross-sectional study in patients with a diagnosis of HHT using Curacao criteria or genetic testing. Methods The ESS questionnaire and Medical Outcomes Study 36-Item Short Form (SF-36) were administered to participants recruited through the HHT Foundation Web site. Demographics and relevant medical histories were collected from all participants. An anchor-based method using a change of 5 in the Physical Component Summary (PCS) of the SF-36 and a distributional method were used to estimate the MID. Results A total of 604 subjects were recruited between April and August 2008. All participants reported epistaxis. An increasing ESS in the study cohort showed a significant negative correlation to the PCS (r = -0.43, P < 0.001). The MID was determined to be 0.41 via the anchor-based approach and 1.01 via the distribution-based approach, giving a mean MID of 0.71. Conclusion Using both the anchor-based and distribution-based approaches, the estimated MID for the ESS in HHT is 0.71. Further implications include key metrics to help guide treatment responses in clinical care and essential information to calculate power and sample size for future clinical trials.