Assessment of Disease Activity in Eosinophilic Esophagitis: Is It Clinically Relevant or Simply an Amusement for Experts?

Background
Since the first description of eosinophilic esophagitis (EoE) as clinicopathologic syndrome three decades ago, considerable progress has been made to standardize and validate instruments to assess symptom severity, quality of life, endoscopic, and histologic activity for the purpose of randomized controlled trials (RCTs) and observational studies. Standardized assessment of EoE activity is crucial to be able to compare the results of therapeutic interventions and bring much needed therapies to patients. This review focuses on outcome assessment of disease activity in adults with EoE.Summary
The choice of endpoints/instruments to be used depends on the setting, which might be either an RCT, an observational study, or clinical practice. In RCTs, the choice of endpoints further depends on requirements from regional regulatory authorities. Primary endpoints chosen in RCTs typically focused on symptoms and esophageal peak eosinophil counts, although that likely will change, as therapies with new mechanism of action are explored. Validated symptom-based PRO instruments used in RCTs include the Daily Symptom Questionnaire (DSQ), the EoE activity index (EEsAI) PRO instrument, and numeric rating scales for dysphagia and pain. Histologic activity in RCT is assessed using the EoE histologic scoring system (EoEHSS) that takes into account the severity and extent of eight distinct histologic features. Endoscopic activity is assessed using the EREFS (Exudates, Rings, Edema, Furrows, Stricture) grading system. For observational studies, activity assessment is based on EEsAI PRO, epithelial peak eosinophil counts, and EREFS. In daily clinical practice, EoE activity is based on assessment of symptoms using a visual analog scale (VAS, from 0-10), peak eosinophil count, and EREFS. Several other instruments including the I-SEE, dysphagia-free days over a defined period, the dysphagia stress test, and impedance planimetry (EndoFLIP), to assess EoE severity in clinical practice are currently under evaluation.Key Messages
EoE activity assessment based on symptom-based PRO, histology, and endoscopy has become increasingly complex and varies depending on the setting. While more stringent endpoints and daily recall PRO instruments are being used in RCTs, new instruments aimed at broader disease activity assessment and weekly recall PRO instruments are being used in observational studies and daily clinical practice.