Clinical effects of Helicobacter pylori outside the stomach

The discovery of Helicobacter pylori infection in the stomach could be considered as one of the most important events of modern gastroenterology. Understanding of the natural history of many disorders of the upper gastrointestinal tract, including chronic gastritis, peptic ulcer disease, gastric cancer and MALT lymphoma, was altered by this discovery. Interestingly, epidemiological studies have also revealed a correlation between H. pylori infection and some diseases localized outside the stomach, especially those characterized by persistent and low-grade systemic inflammation. Of note, H. pylori has an important role in iron deficiency anaemia, idiopathic thrombocytopenic purpura and vitamin B12 deficiency. Moreover, the association of this bacterial pathogen with many other diseases, including hepatobiliary, pancreatic, cardiovascular and neurodegenerative disorders is currently under investigation. In this Review, we summarize the results of the most important studies performed to date surrounding the association of H. pylori infection with extragastric diseases, as well as the strength of the evidence. We also provide information concerning bacterial-host interactions and the mechanisms implicated in the pathogenesis of each of these extragastric diseases.