Autoimmune gastritis as an unexpected cause of diarrhea in a young adult with type I diabetes: a case report.

Background: Type 1 diabetes mellitus (T1DM) is a lifelong diagnosis that involves immune-mediated damage of pancreatic beta cells and subsequent hyperglycemia, manifesting as: polyuria, polydipsia, polyphagia, and weight loss. Treatment of type 1 diabetes centers on insulin administration to replace or supplement the body's own insulin with the goal of achieving euglycemia and preventing or minimizing complications. Patients with T1DM are at risk for developing other autoimmune conditions, most commonly thyroid or celiac disease.

Case Presentation: A 20-year-old African American female with T1DM was referred by her endocrinologist to pediatric gastroenterology for 2 months of nocturnal, non-bloody diarrhea, left lower quadrant pain, and nausea; she was also being followed by neurology for complaints of lower extremity paresthesias and pain. The patient's initial lab-workup was remarkable for a low total Immunoglobulin A (IgA) level of < 6.7 mg/dL. As IgA deficiency is associated with an increased risk of celiac disease, the patient underwent upper and lower endoscopy, which was grossly unremarkable; however, histology revealed a pattern consistent with autoimmune gastritis. Subsequent serum evaluation was remarkable for an elevated fasting gastrin level and an elevated parietal cell antibody level without macrocytic anemia, iron deficiency, or vitamin B12 depletion. The patient was diagnosed with autoimmune gastritis (AIG) and subsequently initiated on parenteral B12 supplementation therapy with improvement in her neurologic and gastrointestinal symptoms.

Conclusion: This case illustrates the importance of recognition of red flag findings in a patient with known autoimmune disease. Following well-established health maintenance recommendations for individuals with T1DM ensures that common comorbidities will be detected. Autoimmune gastritis, while a rarer pathology in the pediatric population, deserves consideration in patients with pre-existing autoimmune conditions and new gastrointestinal or neurologic symptoms, as AIG can be associated with poor outcomes and risk of malignancy. Initial lab findings associated with an eventual diagnosis of AIG typically include anemia, iron deficiency, or Vitamin B12 deficiency. However, as demonstrated in this case, symptoms of AIG can rarely present before anemia or Vitamin B12 deficiency develops. To prevent permanent neurological damage, parenteral Vitamin B12 therapy must be considered even in the absence of Vitamin B12 deficiency, especially in those patients already experiencing neurological symptoms.