Inflammation of colon adenoma in the setting of type 1 autoimmune pancreatitis.

Although immunoglobulin G4-related diseases (IgG4-RD) have been found to affect many organs, little is known about their effects on the colonic mucosae. Pathological examination of colon adenomas has shown inflammatory cell infiltration into the stroma. We therefore assessed the clinicopathological characteristics of colon adenomas in patients with type 1 autoimmune pancreatitis (AIP-1), a representative IgG4-RD. Both colon adenomas from patients with (IgG4 adenomas) and without (Non-IgG4 adenomas) IgG4-RD were characterized by moderate to severe lymphoplasmacytic and eosinophilic inflammation without fibrosis or phlebitis. The ratio of IgG4-positive to IgG-positive plasma cells (IgG4/IgG ratio) and the numbers of IgG4-positive plasma cells were significantly higher in IgG4 adenomas than in Non-IgG4 adenomas. IgG4-positive plasma cells tended to be distributed diffusely in lower areas of the mucosae in IgG4 adenomas. We were unable to confirm whether IgG4 adenomas constituted an IgG4-RD. However, IgG4 adenomas in the setting of IgG4-RD may provide useful pathological information, supplementing a diagnosis of IgG4-RD outside the colon, or may facilitate examination for IgG4-RD, especially AIP-1. IgG4 adenomas warrant further investigation.