Autoimmune Pancreatitis

What happens in autoimmune pancreatitis

In AIP, immune cells (lymphocytes and plasma cells) infiltrate the pancreas and cause inflammation and scarring (fibrosis). The whole gland or part of it swells. Swelling around the head of the pancreas can narrow the bile duct, causing jaundice. The pancreatic duct may also narrow, reducing the flow of digestive enzymes and, over time, affecting insulin production.

Unlike most chronic pancreatitis, AIP is not caused by alcohol or gallstones, rarely causes severe pain, and is reversible with treatment.

Types of autoimmune pancreatitis

Type 1 is the pancreatic form of IgG4-related disease, a multi-organ immune condition.

Symptoms

• Painless obstructive jaundice: yellow skin and eyes, dark urine, pale stools and itching. This is the most common presentation of type 1.
• Mild upper abdominal or back discomfort. Severe pain is unusual.
• Weight loss and tiredness.
• New or worsening diabetes.
• Fatty, pale stools from reduced enzyme production.
• Acute pancreatitis attacks, more common in type 2.
• Symptoms in other organs (type 1): swollen salivary or tear glands, kidney problems, or bile duct narrowing (IgG4-related sclerosing cholangitis).

Diagnosis

Because AIP can look like pancreatic cancer, diagnosis follows the International Consensus Diagnostic Criteria, combining several features:

1. Imaging: CT or MRI shows a diffusely enlarged "sausage-shaped" pancreas with a rim of low density around it (a "capsule-like rim"), or sometimes a focal mass. The pancreatic duct may be narrowed over long segments.
2. Blood tests: a raised serum IgG4 (especially more than twice the upper limit) supports type 1, though a minority of pancreatic cancers also have mildly raised IgG4. Liver tests show a blocked bile duct pattern. CA 19-9 may be checked for cancer.
3. Other organ involvement: imaging or tests showing IgG4-related disease elsewhere.
4. Histology: endoscopic ultrasound-guided core biopsy shows dense lymphocyte and plasma cell infiltration with characteristic fibrosis and many IgG4-positive cells. It also helps exclude cancer.
5. Response to steroids: rapid improvement on scans within 2 to 4 weeks supports AIP. A steroid trial is only done after cancer has been carefully excluded.

Treatment

Steroids

Oral prednisone (or similar) is the first-line treatment. Most people respond within weeks, with jaundice clearing and the pancreas shrinking on scans. The dose is tapered over about 2 to 3 months. Some type 1 patients receive low-dose maintenance therapy because relapses are common.

Bile duct stenting

If jaundice is significant, a plastic stent may be placed in the bile duct during ERCP to relieve the blockage while steroids take effect.

Treatment for relapse

• Rituximab, which depletes B cells, is effective for relapsing type 1 disease and for those who cannot take steroids.
• Azathioprine or mycophenolate are used as steroid-sparing maintenance.

Managing complications

• Diabetes: may improve with treatment but steroids can worsen blood sugar temporarily. See steroid-induced diabetes.
• Pancreatic enzyme replacement for fatty stools and weight loss.
• Bone protection during long steroid courses.

Complications

• Relapse, especially in type 1
• Permanent pancreatic insufficiency and diabetes
• Bile duct narrowing and liver scarring if untreated
• Pancreatic stones in long-standing disease
• A small possible increase in cancer risk, which remains under study

Outlook

The short-term outlook is very good: most patients respond quickly to steroids. Long-term follow-up is needed because type 1 relapses frequently and can involve other organs. Type 2 rarely relapses after initial treatment.

Frequently asked questions

What is autoimmune pancreatitis?

Autoimmune pancreatitis is a rare type of chronic pancreatitis in which the immune system attacks the pancreas, causing swelling and scarring. It often causes painless jaundice and can mimic pancreatic cancer, but it responds well to steroids.

What are the symptoms of autoimmune pancreatitis?

The most common symptoms are painless jaundice (yellow skin and eyes, dark urine, pale stools), mild upper abdominal discomfort, weight loss, tiredness and new diabetes. Severe pain is unusual, unlike other forms of pancreatitis.

How is autoimmune pancreatitis different from pancreatic cancer?

Both can cause painless jaundice and a pancreatic mass on scans. AIP often shows a diffusely swollen pancreas, raised IgG4 and other organ involvement, and improves with steroids. Biopsy is usually needed to rule out cancer before treatment.

Is autoimmune pancreatitis curable?

It can usually be put into remission with steroids. Type 2 rarely comes back. Type 1 relapses in up to half of patients and may need maintenance treatment with low-dose steroids, rituximab or other immune-suppressing medicines.

What causes autoimmune pancreatitis?

The cause is unknown. Type 1 is part of IgG4-related disease, a body-wide immune condition. Type 2 is associated with inflammatory bowel disease. Neither is caused by alcohol or gallstones.