Pancreatogenic diabetes in immunoglobulin G4–related autoimmune pancreatitis managed with automated insulin delivery

Abstract Immunoglobulin G4 (IgG4)-related autoimmune pancreatitis (AIP) may mimic malignancy and lead to progressive pancreatic dysfunction. We describe a 75-year-old man with pancreatic mass lesions, biliary strictures, and elevated carbohydrate antigen 19-9 levels concerning for malignancy. Repeated pancreatic and biliary biopsies demonstrated chronic pancreatitis and fibrosis without carcinoma. Elevated IgG4 levels of 193.5 mg/dL (SI: 1.94 g/L; reference 4-86 mg/dL [SI: 0.04-0.86 g/L]) together with biopsy findings supported AIP. He developed severe exocrine and endocrine pancreatic dysfunction with worsening hyperglycemia and weight loss. Hemoglobin A1c (HbA1c) increased from 7% (SI: 53 mmol/mol) to >17% (SI: >163 mmol/mol; reference 3.8-5.6% [SI: 18-38 mmol/mol]). Autoimmune diabetes antibodies were negative. C-peptide declined over 6 weeks from 1.77 ng/mL (SI: 0.59 nmol/L) to 0.80 ng/mL (SI: 0.26 nmol/L) (reference 1.10-5.50 ng/mL [SI: 0.36-1.82 nmol/L]), supporting pancreatogenic diabetes. Automated insulin delivery achieved sustained glycemic improvement, with HbA1c improving to 7.6% (SI: 60 mmol/mol) at the most recent 18-month follow-up. This case highlights progressive endocrine failure and the utility of advanced diabetes technology in AIP-associated pancreatogenic diabetes.