Another Great Mimicker—Autoimmune Pancreatitis


sinuses, and in multiple pulmonary foci. A CT-guided biopsy of the left submandibular gland showed a mixed chronic inflammatory infiltrate, including numerous IgG4 positive plasma cells with some associated fibrosis and atrophy of the salivary gland parenchyma.


Based on the submandibular gland biopsy results and the PET scan appearance, the diagnosis of IgG4-associated systemic disease (ISD) was made. The patient was started on prednisone 40mg daily and one month later a follow-up PET scan showed significant reduction in the multiple hypermetabolic foci. An MRI of the pancreas also showed improvement in the thickening of the common bile duct and the pancreatic edema. His liver function tests normalized. As the common bile duct stricture looked so suspicious for malignancy on his first two ERCPs, a repeat ERCP with brushings and biopsies was obtained 45 days after starting steroids and found to be negative. The stricture had largely resolved and the stents were removed. The steroid dose was tapered over three months. Because patients with ISD and common bile duct strictures are known to have a high relapse rate,1–3


the patient


was started on azathioprine 2mg/kg. Ten months later he remains asymptomatic and he has normal liver function tests. An MRCP performed one year after starting treatment confirmed that the common bile duct stricture had completely resolved (see Figure 3). There was still some beading and narrowing of the pancreatic duct, although this was much improved compared with previous examinations.


Discussion


Our patient presented with malignant appearing biliary obstruction and pancreatitis but was ultimately diagnosed with ISD with pancreaticobiliary and systemic involvement. Pancreatic involvement in ISD is more commonly referred to as autoimmune pancreatitis (AIP). AIP was first described by Sarles et al. who published a paper in 1961.4 ‘autoimmune pancreatitis’ was coined by Yoshida et al. in 19955


The term and


subsequently the number of cases identified and our understanding of this disease has expanded exponentially.


AIP is rare, with a prevalence in Japan of 0.8/100,000.6 In the US


the prevalence is uncertain but data from surgical series have found AIP in 2.3–11% of pancreatic resections.7–9


AIP represents a unique


subset of chronic pancreatitis with distinct clinical, morphologic, and histopathologic features that typically respond dramatically to corticosteroid treatment.10–13


AIP is now classified into two subtypes,


type I and type II, each with its own clinical and histopathologic features. However, in both types, patients generally present with abdominal pain and obstructive jaundice.10–14


The pathogenesis of AIP is unknown. Current evidence suggests that there may be a genetic susceptibility associated with class II major histocompatibility complex antigens.11,15


An autoantigen such as


antilactoferrin and anticarbonic anhydrase II or IV has been proposed.16 Although serum IgG4 levels are frequently elevated, it is not known if this is pathogenic or an epiphenomenon.11


A microbial agent that can


cause cross-immunoreactivity between microbial agents and endogenous proteins has also been postulated.17


Type I AIP typically occurs in older men in their sixth decade of life.11–13,18 The clinical presentation varies, but the most common presentation is


US GASTROENTEROLOGY & HEPATOLOGY REVIEW


A tight stricture of the common bile duct in the superior half of head of pancreas (horizontal arrow) and irregular beaded narrowing of pancreatic duct in body and tail of pancreas (vertical arrows) can be seen.


that of obstructive jaundice and symptoms of chronic pancreatitis. Rarely, patients present with acute pancreatitis.19


It is common


for patients to have glucose intolerance or diabetes. In the acute phase, patients may present with a focal pancreatic mass. The extrapancreatic manifestations are diverse and include biliary obstruction, salivary gland involvement, mediastinal adenopathy, retroperitoneal fibrosis, and tubulointerstitial fibrosis.10


Bulbous enlargement of tail of pancreas with subtle peripancreatic halo from lymphoplasmacytic infiltrate (arrows) is demonstrated.


Figure 2: Outside Magnetic Resonance Cholangiopancreatography


Figure 1: Outside Computed Tomography Scan in the Venous Phase


Patients may be jaundiced, either


because of entrapment of the intrapancreatic bile duct in an inflamed pancreas, or due to direct involvement of the disease in the bile duct itself.10


Type II AIP patients are younger, usually in their fourth decade 69


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