In this study, we plan to investigate the accuracy of the EG-760Z endoscope (135x zoom) compared with standard imaging with histology as gold standard in detecting and grading inflammatory activity in patients with eosinophilic esophagitis (EoE).

Eosinophilic esophagitis (EoE) is a chronic-inflammatory disease of the esophagus. If left untreated, eosinophilic inflammation induces fibrosis, angiogenesis and stricture formation, finally resulting in a so called remodelling with structural and functional damage of the organ. In addition, patients with untreated EoE are permanently at risk of experiencing food impactions. It is therefore widely accepted that active EoE should be recognized and treated as such. Any treatment applied in EoE should ideally achieve two therapeutic goals: first, resolution of symptoms, and, second, control of inflammation.

However, in some cases of EoE, there is a dissociation between symptoms and histological response.

Furthermore, characteristic endoscopic findings may occur together but are not all seen in every EoE patient. As an example, in 7% to 10% of cases the esophagus may appear normal. Lastly, inflammatory infiltration of the esophageal wall may be discontinuous. In order to define endoscopic activity of EoE in a standardized fashion, the endoscopic reference score (EREFS) is usually applied.

Several endoscopic findings, including linear furrows, concentric rings, white exudates, decreased vasculature in the esophageal mucosa, esophageal strictures, and the esophagus of narrow caliber have been reported to be the characteristic findings of EoE, although neither of these is specific. According to a meta-analysis from 2012, consisting primarily of retrospective studies involving adult cohorts, the overall pooled prevalence of endoscopic findings in patients with EoE was 44% rings, 21% strictures, 9% narrow caliber esophagus, 48% linear furrows, 27% white exudates, and 41% decreased vascularity, with a wide variation in the prevalence of those endoscopic findings between each report.

Lastly, inflammatory infiltration of the esophageal wall may be discontinuous. Taken together, endoscopic recognition of EoE remains a major clinical challenge and diagnosis still relies on histological sampling which in turn renders the diagnosis prone to sampling errors.

In addition to that, it is well known that optimal control of inflammatory activity is crucial in order to prevent progression of fibrosis. Therefore, monitoring inflammatory activity (determined by the EoE histologic scoring system; EoE-HSS) is part of clinical routine in patients with EoE. As outlined above, endoscopic assessment, however, does not reliably reflect the underlying process of the disease during the index endoscopy and cannot be regarded as reliable follow-up test.

The investigators hypothesize that novel endoscopic technologies overcome the shortcomings of the standard endoscopic imaging. It is therefore planned to compare images of the esophageal mucosa using the EG-760Z endoscope by Fujifilm (Fujifilm Europe, Düsseldorf, Germany) to standard imaging with high magnification imaging. This novel endoscope acquires images with a magnification by a factor of 135. As gold standard, histological assessment of the inflammatory activity will be used.

Inclusion Criteria:

Eligible are patients with histology-proven EoE in whom a follow-up endoscopy is indicated. Indications for follow-up endoscopy are i) determination of the response to PPI-Trial or ii) inadequate symptomatic relief despite established therapy.

Type of treatment, or response to, have no implications on eligibility.

Participants fulfilling all of the following inclusion criteria are eligible for the study:

• Patient is capable of giving informed consent
• Informed Consent as documented by signature (Appendix Informed Consent Form)
• Have histology proven EoE and are due to undergo follow-up gastroscopy or are due to undergo gastroscopy to investigate dyspepsia (control group)
• Male and Female patients 18 years to 80 years of age

Exclusion Criteria:

• Contraindications to outpatient gastroscopy
• Contraindication for Non-anesthesia Provider Procedural Sedation and Analgesia: ASA class III or higher, morbid obesity (BMI > 40 kg/m^2), severe OSAS
• Contraindications to tissue sampling: oral anticoagulation in combination with antiaggregant such as aspirin or clopidogrel,
• Patients without subcutaneous veins that allow for insertion of peripheral venous catheters
• Women who are pregnant or breast feeding
• Inability to follow the procedures of the study, e.g. due to language problems, psychological disorders, dementia, etc.
• Participation in another study with investigational drug/device within the 30 days preceding and during the present study
• Previous enrolment into the current study
• Enrolment of the investigator, his/her family members, employees and other dependent persons