Recent understanding of the pathophysiology of functional dyspepsia: role of the duodenum as the pathogenic center

Over almost 30 years since functional dyspepsia (FD) was defined, researchers have endeavored to elucidate the pathophysiology of functional gastrointestinal disorders. Now a consensus is emerging that the gastric symptoms of FD are caused mainly by gastric motility abnormalities and gastric hypersensitivity. The involvement of other causative factors including acid, Helicobacter pylori, psychological factors, and diet has been debated, but how they are involved in the manifestation of dyspeptic symptoms remains unclear. We believe that most of those factors cause FD symptoms by inducing gastric motility abnormalities and gastric hypersensitivity via the duodenum. Here, we discuss 2 possible reasons why patients with FD experience chronic upper abdominal symptoms: (1) the possibility that the contents of the duodenum of patients with FD differ from those of healthy persons and the different contents stimulate the duodenum, and (2) the possibility that the duodenum of patients with FD is more sensitive to noxious stimuli because of low-grade inflammation and increased mucosal permeability.