Autoimmune pancreatitis with colonic stenosis: an unusual complication and atypical pancreatographic finding

BACKGROUND: Type 1 autoimmune pancreatitis (AIP) often accompanies various systematic disorders such as sclerosing cholangitis, sialoadenitis, retroperitoneal fibrosis, interstitial pneumonitis and nephritis. Although rarely reported in acute pancreatitis, colonic stenosis is an uncommon complication in cases with AIP. CASE PRESENTATION: A 69-year-old Japanese man complained of abdominal pain and continuous diarrhea, resistant to intake of antimuscarinic and probiotic agents. A colonoscopy demonstrated a stenosis at the splenic flexure. Computed tomography revealed a focal enlargement of the pancreatic tail with a capsule-like rim, contacting with the descending colon. Endoscopic retrograde pancreatography (ERP) was unable to visualize the main pancreatic duct (MPD) at the pancreatic tail, despite a full contrast injection. A high serum IgG4 level (1060 mg/dL) and exclusion of pancreatic cancer by endoscopic ultrasound guided-fine needle aspiration suggested AIP, but did not fulfill the diagnostic criteria, and steroid therapy was initiated. One month after starting steroid intake, pancreatic swelling was minimized and the MPD was visualized by ERP, fulfilling the international consensus diagnostic criteria (ICDC) of AIP. Colonic stenosis was relieved and the patient’s symptoms disappeared. CONCLUSION: The present case is the first report of AIP developing colonic stenosis by the inflammatory infiltration. In this case, steroid therapy was effective for the diagnosis and treatment of pancreatic mass involving the descending colon.