What can untreated Zollinger-Ellison syndrome lead to?

Untreated Zollinger-Ellison syndrome can lead to severe ulceration of the stomach or duodenum due to the excessive secretion of gastro-enteropeptin, chiefly gastrin, which results in increased gastric acid production. This increased acidity can overwhelm the protective mechanisms of the gastric and duodenal mucosa, leading to the formation of peptic ulcers. These ulcers can become severe and can cause significant complications, including bleeding and perforation.

While the other options, such as chronic diarrhea, and malabsorption of fat-soluble vitamins, may occur in certain contexts or secondary to other conditions, they are not the primary or most direct consequence of untreated Zollinger-Ellison syndrome. Toxic megacolon is typically associated with inflammatory bowel disease or other specific intestinal conditions and does not relate directly to the increased acid production characteristic of Zollinger-Ellison syndrome. Thus, the severe ulceration of the stomach or duodenum is the most critical and direct complication stemming from this condition if left untreated.