Collagenous Gastritis Is an Underdiagnosed Cause of Anemia and Abdominal Pain: Systematic Scoping Review

Background Collagenous gastritis (CG) is a rare disease characterized by infiltration of the lamina propria with mononuclear cells and subepithelial deposition of collagen. Due to its nonspecific presentation, it is often misdiagnosed. The clinical characteristics, endoscopic, and histopathologic features, and treatment outcomes of CG have not been well defined. Aims We aim to summarize the existing evidence of CG. Methods According to the PRISMA Extension for Scoping Reviews, we performed a search on MEDLINE and EMBASE for articles with keywords including “collagenous gastritis” and “microscopic gastritis” from the inception of these databases to August 20, 2022. Results 76 Articles, including nine observational studies, and 67 case reports and series were included. There were 86 cases of collagenous colitis in the final analysis. Most patients presented with anemia (61.4%), followed by abdominal discomfort (60.5%), diarrhea (25.3%), and nausea/vomiting (23.0%). While 60.2% had gastric nodularity on endoscopy, erythema or erosions (26.1%) were also common, as well as normal findings (12.5%). 65.9% of histopathologic findings included subepithelial collagen bands, and 37.5% had mucosal inflammatory infiltrates. Common treatments employed were iron supplementation (42%), followed by PPI (30.7%), prednisone (9.1%), and budesonide (6.8%). Clinical improvement was seen in 64.2%. Conclusion This systematic review summarizes the clinical characteristics of CG. Further studies to establish clear diagnostic criteria and identify effective treatment modalities of this less-recognized entity are needed.