From the Guidelines
Type 2 Autoimmune Pancreatitis (AIP) is characterized by distinct histologic features, including granulocytic epithelial lesions (GELs) with neutrophilic infiltration of the pancreatic duct epithelium and lumen, minimal IgG4-positive plasma cell infiltration, and lack of storiform fibrosis and obliterative phlebitis. The histologic features of Type 2 AIP are crucial for differentiating it from Type 1 AIP and other pancreatic disorders, which is essential for proper diagnosis and treatment planning 1. Some key features of Type 2 AIP include:
- Granulocytic epithelial lesions (GELs) with neutrophilic infiltration
- Minimal IgG4-positive plasma cell infiltration
- Lack of storiform fibrosis and obliterative phlebitis
- Inflammatory infiltrate consisting predominantly of neutrophils, with some lymphocytes and plasma cells
- Areas of acinar atrophy and fibrosis with a more patchy pattern than the storiform pattern seen in Type 1 AIP. It's worth noting that while the provided study 1 discusses autoimmune pancreatitis, it does not specifically differentiate between Type 1 and Type 2 AIP in its description of histologic features, emphasizing the importance of considering the most recent and highest quality studies for definitive recommendations.
From the Research
Histologic Features of Type 2 AIP
The histologic features of Type 2 AIP are distinct from those of Type 1 AIP. Some key features include:
- Granulocytic epithelial lesions, which are characteristic of Type 2 AIP 2, 3, 4
- Only occasional IgG4-bearing plasma cells, typically <10 per high-power field 3
- Idiopathic duct-centric pancreatitis, which is a histologic descriptor for Type 2 AIP 2, 4
- Periductal lymphoplasmacytic infiltration with fibrosis is not a typical feature of Type 2 AIP, but rather of Type 1 AIP 4, 5
- Venulitis and diffuse sclerosis may be present in advanced stages, but are not specific to Type 2 AIP 5
Diagnostic Considerations
Diagnosing Type 2 AIP can be challenging due to the lack of validated serological markers and the similarity in clinical presentation to pancreatic cancer 2, 6. Histology is required for a definitive diagnosis of Type 2 AIP, and the presence of granulocytic epithelial lesions is a key diagnostic feature 3, 4. In cases where histology is not available or is inconclusive, a probable diagnosis of Type 2 AIP can be made based on the presence of inflammatory bowel disease and a response to steroids 6.