S6130 A Zebra Hiding in Plain Sight: The Complex Diagnosis of Autoimmune Enteropathy in a Patient With Refractory Chronic Diarrhea

Introduction: Autoimmune enteropathy (AIE) is a rare, immune-mediated disease characterized by small bowel villous atrophy, associated with chronic diarrhea despite strict diet modifications. Due to its elusive nature, AIE is frequently misdiagnosed and insufficiently treated. Only 200 cases of adult primary/sporadic AIE have ever been reported in the literature, primarily in case reports. We present the diagnosis of AIE in a woman with refractory chronic diarrhea. Case Description/Methods: A 43 year-old woman with a past medical history of lymphocytic colitis presented to the GI clinic for secondary evaluation of chronic diarrhea. The patient reported 10 years of daily intermittent watery diarrhea refractory to multiple anti-diarrheal medications and exacerbated by almost all foods except meat and potatoes. The patient was diagnosed with lymphocytic colitis 10 years prior and treated with an SSRI. She followed a strict gluten-free diet despite negative celiac serologies on multiple evaluations. Additional extensive laboratory testing was negative for other causes of chronic diarrhea, including markers of IBD. Upon initial evaluation in the GI clinic, right and left colon biopsies demonstrated lymphocytic colitis. The patient was treated with daily budesonide with significant improvement of her symptoms. However, 1 year later, she returned with recurrence of her diarrhea despite medication compliance. Esophagogastroduodenoscopy demonstrated diffuse gastric mucosal atrophy and mild intraepithelial lymphocytosis on duodenal mucosal biopsies. Additionally, serum anti-enterocyte antibodies were assessed using indirect immunofluorescence on sections of normal small bowel. Anti-enterocyte IgG stained positive in goblet cell cytoplasm and membranes, suggestive of autoimmune enteropathy. Anti-enterocyte IgM and IgA levels were negative. Patient was started on vedolizumab therapy with 10-pound weight gain, decreased sensitivity to previous dietary triggers, and near complete resolution of her diarrhea. Discussion: AIE shares histopathologic and clinical features with other immunodeficiencies and autoimmune disorders, including celiac disease, making it a challenging diagnosis. In the small number of reported cases in current literature, AIE has shown favorable response to long-term therapy with monoclonal antibodies, specifically integrin-binding antibodies, such as vedolizumab. AIE presents a unique opportunity for advancements in diagnostic criteria and therapeutic objectives through case reports such as this one.