Diagnosis Of Autoimmune Pancreatitis Via Fine Needle Biopsy And Hisort Criteria In A 43-Year-Old African American Male With An Atypical Presentation

INTRODUCTION: Autoimmune pancreatitis (AIP) is a rare disorder characterized by abnormal imaging, elevated IgG4 levels in a majority of cases, typical histology, and usually a perceptible response to steroids. It is further divided into two different subsets, Type 1 and Type 2, with different characteristics and histology. It is difficult to diagnose this condition via a fine needle aspiration (FNA) sample due to scant tissue retrieval; hence other diagnostic criteria like HISORt, as proposed by the Mayo Clinic, are often used. It utilizes histology, imaging, serology, other organ involvement, and response to steroid therapy. CASE DESCRIPTION/METHODS: We report an atypical presentation of autoimmune pancreatitis in a 43-year-old African American male who presented with abdominal pain, diarrhea, a 40 lb weight loss, pancreatic mass, and no known history of autoimmune diseases. Comorbidities include hypertension and diabetes mellitus. An EUS with Fine Needle Biopsy (FNB) was performed, which demonstrated an adequate sample with classic lymphoplasmacytic reaction, which stained positively for IgG4. Serum IgG4 levels were also elevated. A diagnosis of Type 1 AIP was made. The patient’s fecal elastase was low, denoting Exocrine Pancreatic Insufficiency (EPI). He was started on a prednisone taper, along with azathioprine 50 mg and weight-based Creon therapy. Six months post intervention, the patient is symptom free and has regained 15 lbs. DISCUSSION: This case demonstrates the value of the FNB sampling technique to obtain accurate and adequate tissue histology that is not only diagnostic but can further differentiate between Type 1 and 2 AIP, along with validation of the HISORt criteria. In addition, it demonstrates the value of screening for EPI in patients with AIP.Figure 1.: Diffusely thickened appearance of the pancreas and an ill-defined, bi-lobed cystic area at the tail, measuring 1 × 2cm, contiguous with the lower pole of the spleen. Mild splenomegaly and interval development of a slightly irregular cystic splenic mass, measuring 4.5 × 4.3cm.Figure 2.: A 4.8 × 4.1cm oval and hypoechoic lesion at the junction of the body and tail of the pancreas. Calcified mass with a cystic and necrotic component, concerning for a pseudocyst.Figure 3.: A: IgG4 staining, B: MUM-1 staining, C: Storiform fibrosis with lymphoplasmacytic infiltrate, D: Atrophic pancreatic acinar epithelium with fibrosis and inflammation.