Gastric metaplasia: its role in duodenal ulceration.

There is good evidence to suggest that gastric metaplasia in the proximal duodenum and Helicobacter pylori gastritis are essential requirements for the development of duodenal ulceration in most cases. Gastric metaplasia is most likely to be a defence response or adaptation to excess acid reaching the duodenum. The appearance of gastric-type epithelium over the duodenal villi probably results from substitution by cells migrating from Brunner's gland ducts. These metaplastic foci provide sites for colonization by H. pylori passing through the duodenum; the organisms do not attach to native duodenal epithelial cells. Having colonized the metaplastic areas, H. pylori provokes an active chronic inflammatory response akin to that seen in the gastric mucosa. Active chronic duodenitis leads to a weakening of mucosal defence against acid-peptic attack, and erosion and ulceration may ensue. Healing of ulcers by conventional acid-reducing treatments does not influence the extent of gastric metaplasia, (although there may be some reduction with long-term proton pump inhibitors); nor do such regimens affect the background duodenitis. Only with eradication of H. pylori is there resolution of inflammation, but studies to date indicate that eradication alone has no substantial effect on the prevalence or extent of gastric metaplasia. Nevertheless the elimination of H. pylori appears to remove one of the essential co-factors for duodenal ulceration and the patient can be considered cured, despite the persistence of gastric metaplasia.