A 60 year old man has a long history of gastro-oesophageal reflux symptoms, with pain on swallowing. He underwent an upper gastro-intestinal endoscopy 2 months ago, with no malignancy seen. He continues to have difficulty swallowing. His body mass index is 24. What is the most likely cause of his symptoms?
1) Gastrointestinal infection
2) Esophageal stricture
3) Gastric ulcer
4) Hiatal hernia