Background and aims: Autoimmune pancreatitis seems to be a disease with a heterogeneous appearance. Our intention was to establish key diagnostic criteria, define grades of severity and activity, identify features of potential subtypes and evaluate the diagnostic relevance of biopsy specimens.
Methods: Histopathological criteria and clinical features were recorded in pancreatic resection specimens from 53 patients who were found to have chronic pancreatitis lacking pseudocysts, calculi, irregular duct dilatations, pancreas divisum and/or duodenal wall inflammation. The severity of the chronic inflammation was graded, and the activity of the acute inflammatory component and the granulocytic epithelial lesion (GEL) were determined. Additionally, pancreatic biopsy specimens from 9 patients with suspected AIP were assessed.
Results: Periductal lymphoplasmacytic infiltration was identified in all cases, followed in order of frequency by periductal fibrosis and venulitis. These changes were absent in 147 pancreatic specimens that showed chronic pancreatitis associated with pseudocysts, calculi, pancreas divisum and/or duodenal wall inflammation. In 90% of the cases, these chronic changes were graded as 3 or 4. In 81%, the inflammatory process resided in the head of the pancreas and involved the common bile duct. GELs were present in 42% of the patients, who had a mean age of 40.5 years, an almost equal male-female ratio and a high coincidence of ulcerative colitis or Crohn's disease. Patients without GELs were older (mean age 64 years), showed a male preponderance, commonly had Sjogren's syndrome and often developed recurrent bile-duct stenosis. Diagnostically relevant lesions were present in two of five wedge biopsy specimens and three of four fine-needle specimens.
Conclusions: Periductal lymphoplasmacytic infiltration and fibrosis, preferential occurrence in the pancreatic head and venulitis characterize autoimmune pancreatitis. GELs predominantly occur in a subset of patients who are younger, more commonly have ulcerative colitis and Crohn's disease and seem to have fewer recurrences than patients without GELs. Pancreatic biopsy material proved to be a very helpful adjunct for establishing the diagnosis.