S3330 Autoimmune Pancreatitis Masquerading as Peritoneal Carcinomatosis

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INTRODUCTION: Autoimmune pancreatitis (AIP) accounts for approximately 2% of cases of chronic pancreatitis. Type 1 AIP or IgG4 related pancreatitis can present in an acute, recurrent or chronic setting and can have a variety of presentations. In 60-90% of IgG4 related disease, multiple organ systems are involved concurrently. AIP should be considered in all patients with pancreatitis of unclear etiology due to the spectrum of presentation of IgG4 related illness. CASE DESCRIPTION/METHODS: 59-year-old Polish female visiting family in the United States with a history of colon cancer status post right hemicolectomy in Poland 2 years prior to admission who presented with nausea and vomiting. Her symptoms, lipase elevation and CT findings confirmed a diagnosis of pancreatitis. She denied alcohol use and gallstones were not seen on imaging. CT scan was significant for multilobulated pancreatic necrosis with abscesses. Endoscopic ultrasound evaluation showed necrosis without a window for drainage. She then underwent IR guided aspiration of a pancreatic abscess with drain placement and was initiated on IV antibiotics due to concern for infection. In the absence of etiology for her pancreatitis, immunoglobulin labs were sent to evaluate for possible autoimmune etiology. Additionally, imaging also revealed nodularities in the peritoneum concerning for carcinomatosis, which was concerning for possible malignancy given her past history of colon cancer. Tumor markers were within normal limits. IR biopsy of omental nodularity showed fibroadipose tissue with fibrosis, fat necrosis and chronic inflammation. Immunostain was negative for carcinoma. IgG levels came back elevated at IgG4 224 suggesting AIP with possible peritoneal related IgG4 systemic disease. Biopsies were then stained for IgG4 antibodies but were without significant signs of IgG4. Repeat imaging showed no change in pancreatic necrosis/abscess despite daily drain output and antibiotics. A diagnosis of AIP with IgG4 systemic disease was favored and prednisone was started with plans for outpatient follow-up and repeat CT scan. DISCUSSION: AIP is a rare cause of pancreatitis that can present in a variety of ways and can even demonstrate systemic manifestations. Consideration of AIP is important since this is one of the few known treatable etiologies. In conclusion, AIP should be entertained in patients when common causes of pancreatitis have been excluded and signs of systemic disease are noted.