Autoimmune Pancreatitis
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Direct answer
The pancreas that looks like a sausage — diffusely enlarged with a capsule-like rim on CT — in an older man with obstructive jaundice and a raised serum IgG4 is the textbook presentation of type 1 autoimmune pancreatitis, the pancreatic face of IgG4-related disease. Type 2 disease is a younger person's condition, IgG4-negative, histologically defined by granulocytic epithelial lesions and strongly associated with inflammatory bowel disease. Diagnosis assembles imaging, serology, other-organ involvement, histology and steroid response — codified in the International Consensus Diagnostic Criteria and remembered as HISORt. Steroids (prednisolone about 0.6–1 mg/kg per day, tapering over months) induce dramatic remission, but type 1 relapses in roughly 30–50 per cent, at which point maintenance immunomodulation with azathioprine, mycophenolate or rituximab is used. Its greatest danger is surgical: resecting a mass-forming head of pancreas that was merely IgG4 disease all along.
What you must remember
- Type 1 profile: elderly male predominance, diffuse ("sausage") pancreas with a capsule-like rim, raised serum IgG4 (above about 135–280 mg/dL depending on assay cutoff), proximal bile duct strictures mimicking cholangiocarcinoma, and other-organ involvement — sialadenitis, retroperitoneal fibrosis, tubulointerstitial nephritis, orbital disease.
- Type 2 profile: younger patients either sex, serum IgG4 normal, granulocytic epithelial lesions on histology, and inflammatory bowel disease (especially ulcerative colitis) in a substantial minority; relapse after steroid withdrawal is uncommon compared with type 1.
- Histology anchors: type 1 — dense lymphoplasmacytic infiltrate, storiform fibrosis, obliterative phlebitis, and over 10 IgG4-positive plasma cells per high-power field (with the IgG4-to-IgA ratio a refinement); type 2 — the granulocytic epithelial lesion is pathognomonic but patchy.
- ICDC/HISORt assembly: His(ology), Im(aging), S(erology), O(ther organ), R(esponse to steroids), t(reatment course) — no single criterion is mandatory, and points differ between types.
- Steroid protocol: prednisolone about 0.6–1 mg/kg per day (commonly 30–40 mg) for 2–4 weeks with reassessment of imaging, biochemistry and IgG4; taper over 2–3 months; incomplete early response forces re-evaluation for malignancy rather than dose escalation.
- Relapse management: type 1 relapses are common (roughly 30–50 per cent, mostly within the first year or off steroid); options are repeated steroid courses with slower taper, then azathioprine, mycophenolate mofetil, methotrexate or rituximab for refractory disease.
- Cancer exclusion duty: mass-forming autoimmune pancreatitis mimics pancreatic carcinoma (weight loss, painless jaundice, a head mass); CA 19-9 is confounded by cholestasis; EUS with biopsy and a documented steroid response protect against a Whipple performed for inflammation — but steroid trial without tissue carries the equal and opposite risk of delayed cancer surgery, so the workup must be genuinely exhausted first.
- The Indian angle: IgG4-related disease is increasingly recognised in Indian series with pancreatic and biliary presentations dominated by obstructive jaundice; the practical rule — tissue and response documentation before steroids — is the same, and under-diagnosis remains the regional theme.
A worked diagnostic pathway
A 62-year-old man presents with painless jaundice, mild weight loss and a diffusely enlarged pancreas with a rim on CT; ERCP shows a distal bile duct stricture. CA 19-9 is moderately raised (cholestasis, as it often is). Before any steroid, the assembly: IgG4 levels (returned three-fold elevated), other-organ screen (submandibular gland swelling, a renal lesion typical of IgG4 tubulointerstitial nephritis), and EUS-guided core biopsy showing storiform fibrosis with abundant IgG4-positive cells. Prednisolone 40 mg daily is begun and jaundice resolves within two weeks with the pancreatic swelling visibly shrinking at the one-month scan. Taper proceeds over three months; six months later his jaundice returns with a rising IgG4 — a typical type 1 relapse — and azathioprine is added for steroid-sparing maintenance. Every fork here (serology, tissue, response, relapse drug) is examinable, and the one unacceptable fork — upfront steroid trial without workup, or resection without considering the diagnosis — is exactly what the negative-marking options are built from.
How the exam frames it
Stems contrast type 1 with type 2 on four axes: age and sex, IgG4 level, histology (storiform fibrosis and obliterative phlebitis versus granulocytic epithelial lesions) and the inflammatory bowel disease association with type 2. The treatment questions test the taper (relapse is the rule in type 1, so maintenance immunomodulation is a standard answer), and the diagnostic- strategy questions hinge on when a steroid trial is acceptable: after imaging, serology and ideally tissue, never as a shortcut around a cancer workup in a jaundiced elderly mass. Rituximab for refractory IgG4 disease is the modern single-best-answer favourite.
Frequently asked questions
What distinguishes type 1 from type 2 autoimmune pancreatitis?
Type 1 is IgG4-related disease of older men with raised serum IgG4, storiform fibrosis and multi-organ involvement; type 2 is IgG4-negative, shows granulocytic epithelial lesions and associates with inflammatory bowel disease, relapsing far less often.
What histological features define type 1 disease?
Dense lymphoplasmacytic inflammation, storiform fibrosis, obliterative phlebitis and more than 10 IgG4-positive plasma cells per high-power field.
How is steroid response used diagnostically?
Rapid clinical and radiological improvement within two to four weeks of prednisolone 0.6–1 mg/kg supports the diagnosis and is itself a criterion (the R in HISORt); absent response mandates reconsideration of malignancy.
How are relapses managed?
Repeat steroid course with slower taper, followed by maintenance with azathioprine, mycophenolate or rituximab; relapse frequency in type 1 approaches half of patients.
Why must malignancy be excluded before a steroid trial?
Mass-forming autoimmune pancreatitis mimics pancreatic carcinoma, and steroids can transiently shrink a lymphoma or mask a carcinoma, delaying curative surgery — hence imaging, serology and biopsy before treatment.