Pancreatic Dysfunction and Duodenal Inflammatory Responses Coordinate with Refractory Epigastric Pain Including Functional Dyspepsia: A Narrative Review

Some patients with functional dyspepsia (FD) have abnormalities in pancreatic enzymes and chronic pancreatitis. Since 2009, when the idea of early chronic pancreatitis (ECP) first emerged, the utility of endoscopic ultrasonography gained attention, as it can help identify early chronic pancreatitis in patients with dyspepsia. Although the symptoms associated with pancreatic enzyme abnormalities and pancreatic dysfunction overlap with those of dyspepsia, no available data explain the direct relationships and linkages between pancreatic dysfunction and dyspeptic symptoms. Disturbance of exocrine pancreatic enzyme function and reduction in pancreatic endocrine levels, such as insulin, may be associated with dyspeptic symptoms through impaired gastric emptying and duodenal inflammation. Some recent studies have examined the role of duodenal pathophysiology in gastric motility, bicarbonate secretion, and digestion. Because reduced bicarbonate secretion, which is caused by pancreatic dysfunction, leads to a failure to neutralize gastric acid in the proximal duodenum, impaired bicarbonate secretion in turn fails to protect the duodenal mucosa against gastric acid influx, thereby inducing duodenal inflammation. In addition, elevated trypsin levels might be associated in part with duodenal inflammatory responses through PAR2-related immunomodulatory cells. This review describes how duodenal inflammation might affect the pathogenesis of FD and examines whether pancreatic dysfunction is associated with FD through intestinal inflammation. (J Nippon Med Sch 2022; 89: 255?262)