Pseudocysts May Be Seen in Immunoglobulin G4–Associated Autoimmune Pancreatitis

To the Editor.—We wish to comment on the presence of pseudocyst formation referred to by Deshpande et al1 in their comprehensive review of autoimmune pancreatitis (AIP) in the September 2005 issue of Archives of Pathology & Laboratory Medicine. Although the authors mention that pseudocyst formation has been described from a center in Japan,2 other recent publications suggest that pseudocysts do not occur in AIP.3We recently had a case of a 59-year-old male patient with a severe bout of abdominal pain. A pancreatic tail pseudocyst had been diagnosed on computed tomographic scan the previous year. The repeat scan revealed enlargement since the prior examination with extension into the spleen (Figure 1). There was no calcification, and the head, neck, and body of the pancreas were unremarkable. The biliary tree was normal and there were no gallstones. Liver function test results were normal; there was a mildly elevated serum lipase of 150 U (local reference range, 0–60 U/L) noted on presentation; and an episode of anemia (Hgb 9.4 g/dL) occurred prior to surgery.The resection specimen showed a complex pseudocyst, with the typical lining of fibrinohemorrhagic exudate, and granulation tissue, which effaced the tail of the pancreas and extended into the spleen. The residual parenchyma showed dense sclerosis with atrophy of lobules, lymphoplasmacytic infiltrate, focal venulitis, and perivascular and periductal fibrosis (Figure 2). The plasma cells stained strongly for immunoglobulin (Ig) G4 (clone 05-3800; Zymed Laboratories Inc, San Francisco, Calif). The resection margin at the pancreas body showed minimal inflammation, suggesting that this process was restricted to the distal pancreas, correlating with the computed tomographic findings.The patient denied any significant alcohol intake, and did not show any other stigmata of autoimmune disease or diabetes mellitus. The serum IgG4 was elevated at 281 mg/dL (reference range, 7–74 mg/dL) and the IgG level was normal.Autoimmune pancreatitis is an incompletely defined entity. Other diagnostic terms are lymphoplasmacytic sclerosing pancreatitis and nonalcoholic duct destructive chronic pancreatitis. Diagnostic features, as outlined in the review by Deshpande et al,1 include ruling out of other causes, elevated immunoglobulins, presence of autoantibodies, stigmata of autoimmune or inflammatory-fibrosing disease in other organs, and the characteristic fibroinflammatory pancreatic lesion. The exact diagnostic significance of IgG4-positive plasma cells is unclear. Deshpande et al4 have additional data that show significantly more IgG4 plasma cells in AIP, but the presence of IgG4 plasma cells in 57.1% of pancreatitis not otherwise specified and in 47.4% of duct carcinoma of the pancreas. Increased numbers of IgG4 plasma cells may nevertheless contribute to the diagnosis in the correct setting. These patients also characteristically have raised serum IgG4 levels.The case reported by Nishimura et al2 of pseudocyst formation in AIP was purported to be the first in the English language literature. We were able to find one additional report of AIP in which a radiologic fluid-filled cavity suggested a pseudocyst.5 Our case would thus potentially represent the fifth reported case.The presence of pseudocyst formation does not exclude AIP, and suggests that bouts of acute inflammation and tissue destruction with cyst formation can occur, possibly related to duct destruction and distal stasis.

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