Ampullary pseudotumour: an endoscopic clue to autoimmune pancreatitis.

The Editor, Sir, A 63-year old man with Type 2 diabetes mellitus for approximately 10 years presented with epigastralgia, anorexia and weight loss of 16 kg over four months. He had been diagnosed with pancreatitis four months previously, which became inactive after supportive management. His initial blood tests including liver and pancreatic biochemistries were grossly unremarkable. Panendoscopy for the upper gastrointestinal symptoms yielded a smooth-surfaced pseudotumour (black arrow) around the major duodenal papilla (white arrowhead) at the ampulla of Vater (Fig. 1). The subsequent abdominal computed tomography displayed a 1 cm nodular lesion in the ampullary area (black arrowhead), and a diffusely enlarged pancreas (white arrowheads) with an extreme protrusion in the pancreatic head [white arrows] (Figs. 2 and ​and3).3). Further diagnostic approaches revealed an elevated serum immunoglobulin (Ig) G4 level of 1470 (reference 3–201) mg/dL and a gamma globulin level of 38.1% (reference 9–18), along with an extensive lymphoplasmacytic infiltration in the specimens of endoscopic ampullary pseudotumour biopsy. The diagnosis of autoimmune pancreatitis (AIP) was established, and oral prednisolone was prescribed which was gradually tapered from a daily dose of 40 mg to 2.5 mg as a maintenance dose. The patient got dramatic clinical and radiographical improvement which lasted during the one-year follow-up period to date. Fig. 1 Panendoscopy in the 63-year old patient showing a smoothsurfaced protrusion (black arrow) around the major duodenal papilla (white arrowhead) at the ampulla of Vater. Fig. 2 Contrast-enhanced abdominal computed tomography displaying a 1-cm diameter nodular lesion in the ampullary area (black arrowhead), along with an extremely protrusive enlargement in the pancreatic head (white arrows). Fig. 3 Contrast-enhanced abdominal computed tomography revealing a diffuse enlargement of the pancreas (white arrowheads). Autoimmune pancreatitis is an autoimmune-associated entity accounting for 5–6% of chronic pancreatitis (1). It commonly presents with jaundice, vague abdominal pain and weight loss. Major duodenal papilla swelling was reported in 24% of AIP patients (2), but protrusion as a pseudotumour is fairly unique (3). Currently, AIP is diagnosed based on a combination of imaging, serological and histologic studies. Differentiating AIP from pancreatic cancer is challenging because of the similar clinical and imaging presentations. However, AIP has a dramatic response to steroid therapy. Immunoglobulin G4-immunostaining of biopsy specimens from major duodenal papilla is supportive of diagnosing AIP (2). Accurate diagnosis may avoid unnecessary surgery and delay in the administration of steroid therapy.