Case Report: Recurrent abdominal pain with elevated pancreatic enzymes in type 2 diabetes mellitus: a case of IgG4-related autoimmune pancreatitis misdiagnosed as acute pancreatitis.

Background: IgG4-related autoimmune pancreatitis (IgG4-AIP) is a rare autoimmune pancreatic disorder with non-specific clinical manifestations that is often misdiagnosed as acute pancreatitis (AP). Its coexistence with type 2 diabetes mellitus (T2DM) may further complicate recognition of the underlying pancreatic disease. Case presentation: A 60-year-old male with a 4-year history of T2DM was admitted for diabetic complications manifesting as blurred vision and lower limb numbness. During hospitalization, he developed recurrent epigastric pain associated with elevated pancreatic enzymes and was initially diagnosed with AP. Conventional treatment for AP did not lead to sustained improvement, and amylase and lipase remained persistently elevated. Serum IgG4 was markedly elevated at 13.8 g/L. Imaging findings were unremarkable. Endoscopic ultrasound-guided fine-needle aspiration revealed chronic inflammatory changes. The diagnosis of IgG4-AIP was ultimately established based on the markedly elevated serum IgG4 level, supportive (though atypical) imaging findings, histopathological features, and a favorable response to glucocorticoid therapy. The patient's symptoms improved, accompanied by an overall decrease in serum IgG4 and pancreatic enzyme levels. Conclusion: In T2DM patients with recurrent abdominal pain and persistently elevated pancreatic enzymes unresponsive to routine AP treatment, IgG4-AIP should be considered. Timely measurement of serum IgG4 and careful integration of imaging, histopathology, and treatment response are important for early diagnosis. Early recognition may prevent misdiagnosis and enable timely initiation of glucocorticoid therapy.