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Autoimmune pancreatitis: A mimic of pancreatic cancer

Cleveland Clinic Journal of Medicine. 2009 October;76(10):607-615 | 10.3949/ccjm.76a.09039
October 1, 2009|Cleveland Clinic Journal of Medicine
Ryan Law, DO;Mary Bronner, MD;David Vogt, MD;Tyler Stevens, MD
Author and Disclosure Information

Ryan Law, DO
Department of General Internal Medicine, Cleveland Clinic

Mary Bronner, MD
Section Head, Morphologic Molecular Pathology, Pathology and Laboratory Medicine Institute, Cleveland Clinic

David Vogt, MD
Departments of Hepato-pancreatobiliary and Transplant Surgery, General Surgery, and Transplantation Center, Digestive Disease Institute, Cleveland Clinic

Tyler Stevens, MD
Digestive Disease Institute, Cleveland Clinic

Address: Tyler Stevens, MD, Digestive Disease Institute, A31, Cleveland Clinic, 9500 Euclid Avenue, Cleveland, OH 44195; e-mail stevent@ccf.org

ABSTRACTAutoimmune pancreatitis is an idiopathic inflammatory disease that produces pancreatic masses and ductal strictures. This benign disease resembles pancreatic carcinoma both clinically and radiographically. The diagnosis of autoimmune pancreatitis is challenging to make. However, accurate and timely diagnosis may preempt the misdiagnosis of cancer and decrease the number of unnecessary pancreatic resections.

KEY POINTS

  • Hallmark features of autoimmune pancreatitis include an elevated serum immunoglobulin G4 level, focal or diffuse pancreatic enlargement on imaging, and dense lymphoplasmacytic infiltrates on histologic study.
  • The disease can be associated with extrapancreatic manifestations, including sclerosing cholangitis, sialadenitis and retroperitoneal fibrosis.
  • Autoimmune pancreatitis responds dramatically to corticosteroid treatment.

DIAGNOSIS IS IMPROVING

The diagnosis of autoimmune pancreatitis has improved, thanks to a growing awareness of the condition. The most widely accepted diagnostic criteria come from Korea, Japan, and the United States (Table 2).9–13 Efforts to establish international diagnostic criteria are under way.9,14

Laboratory findings

Serum amylase and lipase are neither sensitive nor specific for autoimmune pancreatitis. Usually, their values are within normal limits or only mildly elevated.

A cholestatic pattern of elevation (elevated alkaline phosphatase and bilirubin, with normal or only slightly elevated alanine and aspartate aminotransferases) is found in patients with an inflammatory mass in the pancreatic head and in those with autoimmune sclerosing cholangitis. In one series,4 pancreatic enzymes were elevated in only 3 (13%) of 17 cases, while cholestasis was present in 16 (94%).

Gamma globulin, total IgG, and IgG4 are commonly elevated in autoimmune pancreatitis. Serum IgG4 is considered the most sensitive and specific marker and is elevated in 63% to 94% of patients with autoimmune pancreatitis.4,15–17 Several studies found the diagnostic accuracy, sensitivity, and specificity to be highest (> 90%) when a cut point of 135 mg/dL was used.17,18 A subsequent study 15 revealed a sensitivity of 76% and a specificity of 93% using the same cut point. Recall that the IgG4 level in our patient was 380 mg/dL.

Autoantibodies that are elevated in autoimmune pancreatitis include antilactoferrin antibodies and anticarbonic anhydrase II antibodies. 19 Both are “organ-specific”: the former are found in pancreatic acinar cells, and the latter are found in ductal cells. The sensitivity of both antibodies is greater than 50% in patients with autoimmune pancreatitis. However, they are not often measured, since testing for them is not widely available.20,21

Antinuclear antibody and rheumatoid factor are also associated with autoimmune pancreatitis but are not very specific.

Radiographic findings

The most common radiographic feature is diffuse enlargement of the entire pancreas. The appearance of the gland is often described as “sausage-like,” a feature best seen with CT and magnetic resonance imaging (MRI).

Figure 2. Dual-phase helical computed tomography shows focal enlargement of the pancreatic tail (arrow) in a patient with autoimmune pancreatitis.
However, sometimes the pancreas is focally enlarged (ie, with an “inflammatory mass”) as in our patient (Figure 2). Delayed pancreatic enhancement on CT and MRI is due to inflammation, edema, and fibrosis.22

A well-defined capsule-like rim surrounding the pancreas is another common feature.23 This rim-enhancement is hypointense on T2 MRI, suggesting the presence of peripheral inflammation and fibrosis.

Calcifications and pseudocysts are rarely seen in autoimmune pancreatitis.

On ultrasonography, the involved pancreatic parenchyma appears hypoechoic, consistent with edema.

Endoscopic retrograde cholangiopancreatography

ERCP or magnetic resonance cholangiopancreatography may reveal segmental or diffuse narrowing of the main pancreatic duct.24,25 Bile-duct strictures may occur throughout the biliary tree.23

Autoimmune pancreatitis with biliary involvement must be distinguished from primary sclerosing cholangitis because the former responds to corticosteroid treatment. Cholangiographic features in primary sclerosing cholangitis include band-like strictures and a beaded or “pruned-tree” appearance, while autoimmune pancreatitis more commonly produces long strictures with prestenotic dilatation.26

ERCP allows temporary stents to be placed in obstructed segments of the biliary tree to open them up in the setting of acute cholangitis.

Biopsy guided by endoscopic ultrasonography

Some have proposed using endoscopic ultrasonography to guide biopsy in cases of suspected autoimmune pancreatitis.27,28

Fine-needle aspiration biopsy, guided by endoscopic ultrasonography, is frequently used to rule out adenocarcinoma. However, its yield for cancer is not perfect (about 70%–90%), so a negative biopsy does not rule out cancer. Further, autoimmune pancreatitis is rare, so a patient with a negative finding on fine-needle aspiration biopsy is still more likely to have cancer than autoimmune pancreatitis. In this case, the negative study should be combined with other information (eg, IgG4) to decide whether empiric treatment should be given.

Core biopsy, also guided by endoscopic ultrasonography, collects a greater amount of tissue for analysis and may allow the histologic diagnosis of autoimmune pancreatitis, but it carries a greater risk of bleeding. Also, its yield may be lower than initially thought. In one series, only 26% of ultrasonographically guided core samples from patients with confirmed autoimmune pancreatitis had diagnostic histologic features.29

New immunohistologic techniques are being developed to increase the yield from cytologic and tissue specimens.

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