The goal of this observational study is to learn whether heterotopic gastric mucosa (HGM) in the upper esophagus is associated with swallowing difficulties (dysphagia) in adults undergoing a medically indicated gastroscopy. The main questions it aims to answer are:

• Is the presence of HGM associated with dysphagia?
• Is the presence of HGM associated with dyspepsia and reduced health-related quality of life? Among participants reporting dysphagia, what is the distribution of oropharyngeal versus esophageal dysphagia, and is this related to the presence of HGM? If there is a comparison group: Researchers will compare participants with endoscopically confirmed HGM to participants without HGM to determine whether dysphagia, dyspepsia symptoms, and quality-of-life measures differ between groups.

Participants will:

Complete pseudonymised questionnaires about dysphagia, dyspepsia symptoms, and quality of life before the gastroscopy.

Undergo the medically indicated gastroscopy as planned; the endoscopist will assess whether HGM is present based on the endoscopic appearance, and routine endoscopy findings will be documented.

Heterotopic gastric mucosa (HGM) consists of islands of gastric-type mucosa located in the proximal esophagus, typically just below the upper esophageal sphincter. HGM is frequently detected incidentally during upper GI endoscopy, and its clinical relevance remains incompletely understood. Retrospective data suggest that HGM may be associated with symptoms such as dysphagia and dyspepsia; however, prospective data and information on health-related quality of life are limited.

This is a prospective, observational, single-center study conducted in adults (≥18 years) undergoing clinically indicated gastroscopy for any indication. The primary objective is to investigate the association between HGM and dysphagia. Secondary objectives are to evaluate associations between HGM and dyspepsia and impairment of quality of life, and to differentiate oropharyngeal versus esophageal dysphagia. An additional exploratory objective is to assess whether symptom patterns vary by histological subtype when histology is available from routine care.

After informed consent, participants complete paper-based, pseudonymised questionnaires prior to endoscopy (estimated completion time ~30-45 minutes). Oropharyngeal dysphagia is assessed using the Sydney Swallowing Questionnaire (SSQ, German version), and esophageal dysphagia using the Eating Assessment Tool-10 (EAT-10, German version). Dysphagia-related quality of life is assessed with the M.D. Anderson Dysphagia Inventory (MDADI, German validated version/D-ADI). Dyspepsia symptom burden and related quality of life are assessed using the Gastrointestinal Symptom Rating Scale (GSRS) and Quality of Life in Reflux and Dyspepsia (QOLRAD). The endoscopist is blinded to questionnaire results. During routine gastroscopy, the proximal esophagus is carefully inspected (preferably using Narrow Band Imaging) and the presence or absence of HGM is documented; participants are assigned to HGM or control (no HGM) groups. No additional procedures are mandated by the study; routine endoscopy and any clinically indicated histology are recorded as available.

Data are collected and stored in pseudonymised form and analyzed statistically (planned recruitment period ~12 months). The anticipated total sample size is 731 participants.

Inclusion Criteria:

• Planned upper gastrointestinal endoscopy (gastroscopy) for clinical reasons (any indication)
• Age ≥ 18 years
• Written informed consent
• Ability to complete the study questionnaires prior to endoscopy

Exclusion Criteria:

• Previously known heterotopic gastric mucosa (HGM)
• Previously diagnosed dysphagia with prior therapeutic intervention (including pre-established diet modification, partial oral/enteral nutrition, steroid therapy, botulinum toxin injection, etc.)
• Mechanical ventilation
• Presence of a tracheostomy
• Inadequate endoscopic assessability of the proximal esophagus, including:
• General condition insufficient for careful endoscopic inspection (investigator's judgement)
• Increased risk of aspiration
• Inadequate visibility during the procedure (e.g., bleeding, food residue)
• Complications preventing careful inspection of the proximal esophagus
• History of surgery involving the pharynx or esophagus
• Relevant severe neurological disorder (e.g., ALS, stroke)
• Severe dementia
• Severe depressive disorder
• Lack of cooperation / inability to comply with study procedures
• Planned PEG placement
• Emergency endoscopy

Adults (≥18 years) undergoing clinically indicated upper gastrointestinal endoscopy (gastroscopy) at a single center will be consecutively screened and invited to participate over a 12-month period. After informed consent, participants complete symptom and health-related quality-of-life questionnaires prior to endoscopy. During routine gastroscopy, the presence or absence of heterotopic gastric mucosa (HGM) in the proximal esophagus is assessed based on endoscopic appearance (and histology from routine care if available). Participants are grouped as HGM present vs no HGM for comparative analyses.

Individual participant data (IPD) will not be shared. Only aggregated results will be published; data access is restricted due to data protection requirements and the wording of the informed consent.