Abstract

Background and aims: Oesophageal pH is conventionally recorded from a point 5 cm above the lower oesophageal sphincter. However, the mucosal changes of reflux oesophagitis and intestinal metaplasia tend to affect the segment of oesophagus distal to this and close to the squamocolumnar junction. This study set out to investigate oesophageal acid exposure of squamous mucosa close to the squamocolumnar junction.

Methods: Dual channel 24 hour pH monitoring was carried out in 11 patients with endoscopy negative dyspepsia and no evidence of gastro-oesophageal reflux by conventional oesophageal pH metry. Oesophageal pH was recorded from electrodes positioned 5 mm and 55 mm proximal to the squamocolumnar junction. A novel technique was developed using metal clips to secure the pH catheter to the oesophageal mucosa and maintain these electrode positions. Oesophageal manometry indicated that the distal electrode was within the high pressure zone of the lower oesophageal sphincter.

Results: We found that 24 hour oesophageal acid exposure (per cent time pH <4) was greater 5 mm above the squamocolumnar junction compared with the conventional position 5 cm more proximal (11.7% v 1.8%; p<0.001). The greater acid exposure at the distal versus the conventional site was apparent in both the upright (12.7% v 2.3%) and supine (10.5% v 1.3%) positions, as well as during preprandial (14.2% v 1.6%) and postprandial (21.8% v 2.8%) periods (p<0.001 for each). The number of reflux events recorded close to the squamocolumnar junction was also higher than at the conventional position (168 v 33; p<0.001). There was no correlation between acid exposure at the two sites.

Conclusions: The squamous mucosa of the most distal oesophagus is exposed to substantial acidic reflux, even in patients without evidence of conventional reflux disease. This short segment reflux may explain the high incidence of metaplasia and neoplasia at the gastro-oesophageal junction.