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Autoimmune pancreatitis: A mimic of pancreatic cancer

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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.


 

References

A 66-year-old Korean man presented with a 2-week history of progressive jaundice, mild epigastric discomfort, and a weight loss of 12 lb. His serum bilirubin level was 5.8 mg/dL (reference range 0.0–1.5), and his alkaline phosphatase level was 325 U/L (20–120). Computed tomography (CT) revealed a 3-cm mass in the head of the pancreas.

Figure 1. Endoscopic ultrasonographic image showing fine-needle aspiration of a hypoechoic mass (arrow) in the head of the pancreas.

Endoscopic retrograde cholangiopancreatography (ERCP) revealed a tight stricture in the intrapancreatic portion of the common bile duct. Brush cytology was negative for malignant cells. A plastic stent was placed to help palliate the jaundice. Endoscopic ultrasonography done at the same time revealed a hypoechoic mass in the head of the pancreas abutting the portal vein. Endoscopic ultrasonography-guided fine-needle aspiration biopsy was negative for malignant cells (Figure 1).

Exploratory laparotomy revealed a fibrotic pancreas with a palpable mass in the pancreatic head. The mass was unresectable, as it was adhering to the portal vein. A choledochoduodenostomy (anastamosis of the common bile duct to the duodenum) was created for palliation of jaundice. Intraoperative core biopsy revealed destruction of the pancreatic acinar architecture by marked lymphoplasmacytic inflammation and lymphocytic and obliterative venulitis, consistent with autoimmune pancreatitis.

Immediately after surgery, his serum immunoglobulin G4 (IgG4) level was 380 mg/dL (reference range 1–112). His bilirubin and alkaline phosphatase values came down into the normal range in the immediate postoperative period, and his jaundice resolved after a few days.

A CHRONIC INFLAMMATORY CONDITION

Autoimmune pancreatitis is a chronic inflammatory condition with distinct clinical, radiographic, and histologic features.

Sarles et al,1 in 1961, were first to propose that autoimmunity may be a factor in chronic pancreatitis. Three decades later, autoimmune pancreatitis was codified as a separate disease on the basis of a case report of a patient with serum elevations of IgG and gamma globulin, pancreatic duct narrowing, lymphocytic infiltration, fibrosis, and a marked response to steroid therapy.2 Yet its pathogenesis remains poorly understood.

Extrapancreatic manifestations include sclerosing sialadenitis, sclerosing cholangitis, and retroperitoneal fibrosis.

Of note, autoimmune pancreatitis can mimic pancreatic adenocarcinoma clinically and radiographically. One must differentiate between the two disorders to prevent unnecessary surgery or delay in corticosteroid therapy.

RATES ARE POORLY DEFINED

The exact prevalence and incidence of autoimmune pancreatitis remain poorly defined. Most of the initial epidemiologic data have come from Japan and Korea. The prevalence was 0.7 per 100,000 patients in a survey of the Japanese population.3 Further studies are needed to ascertain its incidence and prevalence in the United States.

In patients with chronic pancreatitis, the estimated prevalence is between 4.6% and 6%, and 11% in patients undergoing pancreatic resection for suspected pancreatic cancer.4,5

Autoimmune pancreatitis appears to be a disease of the elderly, as most patients are more than 50 years old at diagnosis. Twice as many men as women are affected.5 Many patients have no history of alcohol abuse or other traditional risk factors for chronic pancreatitis.

CLINICAL PRESENTATION: PAINLESS JAUNDICE, WEIGHT LOSS

Table 1 lists the typical clinical features of autoimmune pancreatitis.

The most common clinical presentation is obstructive jaundice with little or no abdominal pain. In one series,4 65% of patients presented with painless jaundice secondary to biliary obstruction. Obstructive acute pancreatitis can occur, due to inflammatory strictures of the main pancreatic duct.

Weight loss results from impaired digestion and decreased appetite. Autoimmune pancreatitis is complicated by pancreatic exocrine insufficiency in 88% of cases6 and by endocrine dysfunction in 67%.3

Many patients have extrapancreatic lesions such as sclerosing sialadenitis, retroperitoneal fibrosis, and autoimmune sclerosing cholangitis.7 The cholangiographic appearance of autoimmune sclerosing cholangitis may resemble that of primary sclerosing cholangitis or cholangiocarcinoma. Less common extrapancreatic findings include interstitial nephritis and mediastinal adenopathy. These extrapancreatic findings do not always coincide with pancreatic inflammation. The histopathologic findings in extrapancreatic lesions parallel those in the pancreas.8

The patient described at the beginning of this article had several of these features, including painless jaundice, weight loss, elevated alkaline phosphatase, and an inflammatory pancreatic mass.

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