From the Guidelines
Autoimmune pancreatitis (AIP) is diagnosed through a combination of clinical features, imaging, serology, and sometimes histology, with the most recent guidelines suggesting the use of abdominal imaging, elevated serum IgG4 levels, and response to steroid therapy as key diagnostic criteria 1. Diagnosis of AIP typically requires:
- Abdominal imaging (CT or MRI) showing characteristic pancreatic enlargement or "sausage-shaped" pancreas
- Elevated serum IgG4 levels (>135 mg/dL)
- Response to steroid therapy Other diagnostic criteria include:
- Narrowing of the pancreatic duct on ERCP
- Presence of other organ involvement
- Histological features of autoimmune pancreatitis (AIP)/IgG4-associated cholangitis (IAC) or classical imaging findings of AIP and elevated IgG4 1 Treatment primarily consists of corticosteroid therapy, usually starting with prednisone 40mg daily for 2-4 weeks, followed by a gradual taper over 3-6 months 1. The steroid response is so characteristic that it's considered a diagnostic criterion, with failure to respond prompting reconsideration of the diagnosis 1. For relapsing disease, steroid-sparing immunomodulators like azathioprine (2-2.5 mg/kg/day), mycophenolate mofetil (1000-1500mg twice daily), or rituximab (typically two 1000mg infusions given two weeks apart) may be used 1. Long-term maintenance therapy is often necessary in type 1 AIP, with regular monitoring of pancreatic function important as some patients develop exocrine or endocrine insufficiency requiring enzyme replacement or diabetes management 1. Key clinical features that differentiate IgG4-related sclerosing cholangitis (IgG4-SC) from primary sclerosing cholangitis (PSC) include:
- Pancreatic mass or enlargement on CT
- Pancreatic ductal abnormalities
- Raised serum IgG4
- Ampullary biopsy with >10 IgG4 plasma cells per high power field
- Liver/tissue biopsy with >10 IgG4 plasma cells per high power field
- Pancreatic exocrine insufficiency
- Other associated systemic fibrosclerotic disease
- Improvement with steroid treatment 1
From the Research
Diagnosis of Autoimmune Pancreatitis
The diagnosis of autoimmune pancreatitis (AIP) is difficult and should be made by a comprehensive evaluation of:
- Clinical findings
- Radiological findings
- Serological findings
- Pathological findings 2 There are several established diagnostic criteria systems that are used to diagnose AIP, which rely on a combination of:
- Imaging findings of the pancreas and other organs
- Serologic findings
- Pancreatic histologic findings
- Response to corticosteroid therapy 3
Diagnostic Tools
Some diagnostic tools that can be used to support a diagnosis of AIP include:
- Immunoglobulin (Ig)G4-immunostaining of biopsy specimens obtained from the major duodenal papilla 4
- Serum immunoglobulin IgG or IgG4 and antibodies (rheumatoid factor, lactoferrin antibodies, carbonic anhydrase II, etc) 5
- Imaging changes, such as pancreas enlargement and pancreatic duct narrowing 5
- Histopathological markers, such as lymphoplasmatic infiltration and pancreatic parenchyma fibrosis 5
Treatment of Autoimmune Pancreatitis
The standard therapy for AIP is oral administration of corticosteroids 2 Other treatment options include:
- Rituximab (RTX) for induction of remission and maintenance therapy in relapsing AIP-1 2
- Immunomodulators, such as azathioprine, to maintain remission 2
- Biologic drugs, such as anti-tumor necrosis factor (TNF) therapy, as a second-line therapy for AIP type 2 relapses or steroid dependence 2 Steroid treatment with an initial dose of 30 or 40 mg prednisone is effective and safe in most patients with AIP 6