Periaortitis and Retroperitoneal Fibrosis in a Patient With a Normal IgG4 Level: A Case Report and Review of the Literature.

We present a case of IgG4-related periaortitis with retroperitoneal fibrosis (RPF) in a 66-year-old man with a complex medical history, including coronary artery disease, hypertension, and prediabetes. The patient presented with abdominal and flank pain, and imaging revealed inflammatory changes surrounding the abdominal aorta and splenic artery. Treatment with corticosteroids resulted in significant symptomatic improvement. This case is compared with previously reported cases of periaortitis, including those associated with endovascular aortic repair (EVAR) and idiopathic IgG4-related disease (IgG4-RD). We highlight the similarities and differences in clinical presentation, underlying etiology, and response to treatment. In this case, the diagnosis was based on the clinical presentation, radiological findings, and favorable response to corticosteroid therapy, despite normal serum IgG4 levels. This case highlights the importance of considering IgG4-RD in the differential diagnosis of periaortitis and RPF, even when laboratory findings, including serum IgG4 levels, are within the normal range.