Objectives: In autoimmune pancreatitis (AIP), the prevalence, interrelationships, and significance of peripheral eosinophilia, allergic disorders, and eosinophil infiltration in the pancreas remain unclear. Methods: From medical records, we obtained data on peripheral eosinophil counts at presentation and follow-up, and clinical diagnoses of allergic disorders in 97 AIP patients (78 type 1 and 19 type 2), which were compared with matched healthy controls. Available pancreatic histologic specimens were graded for eosinophils. Peripheral eosinophilia was defined as counts 0.5 × 10 9 per liter. We examined nature of and association between these parameters in AIP. Results: Among 78 type 1 AIP patients (mean age 6214 years, 77% men), peripheral eosinophilia at presentation was diagnosed in 12% and allergic disorders in 15% (vs. 0 and 4% in controls, P0.0004 and 0.006, respectively). Allergic disorders were observed in 27 and 11% of type 1 AIP with and without eosinophilia, respectively (P0.08). Patients with and without peripheral eosinophilia were similar in clinical profile. Moderate-to-severe eosinophil infiltration was present in 67% of pancreas resection specimens and did not correlate with peripheral eosinophilia. Type 2 AIP did not differ from type 1 AIP in any of these parameters. Conclusions: Peripheral eosinophilia, allergic disorders, and pancreatic eosinophil infiltration are associated with AIP. Eosinophilia in AIP may not reflect an allergic phenomenon, but appears to be consistent with autoimmune mechanism.
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