A 61-Year-Old Woman Presenting with Low Back Pain Diagnosed with IgG4-Related Disease Affecting the Thoracoabdominal Aorta and Retroperitoneum.

BACKGROUND Immunoglobulin G4-related disease (IgG4-RD) includes several immune-mediated fibro-inflammatory conditions affecting multiple organs. Increased IgG4 serum levels support the diagnosis of IgG4-RD and characteristic histopathology of fibrous infiltrates or masses containing IgG4-positive plasma cells. We present the case of a 61-year-old woman with low back pain who was diagnosed with IgG4-RD involving the thoracoabdominal aorta and retroperitoneum. CASE REPORT A 61-year-old woman who had persistent low back pain was referred to a university hospital in South Korea. Computed tomography (CT) and 2-[18F]-fluoro-2-deoxy-D-glucose positron emission tomography/CT (F-18-FDG-PET/CT) demonstrated diffuse circumferential infiltrates from the thoracoabdominal aorta, iliac vessels, and retroperitoneum associated with right obstructive uropathy. The serum IgG4 concentration was 418.0 mg/L (reference range: 30-2000). She underwent laparoscopic retroperitoneal biopsy and received a cystoscopic double-J ureteral stent. IgG4-positive plasma cells, lymphoplasmacytic infiltration, and fibrosis were observed on histopathological examination. She was diagnosed with IgG4-RD and treated with glucocorticoids (GCs) for 6 months. She underwent femoral-to-femoral bypass graft surgery for revascularization due to occlusion of the right iliac arteries. She experienced relapse after GC discontinuation, and GC administration was resumed. She had difficulty tapering GC use owing to persistent low back pain, which improved with combined treatment of GC and immunosuppressant. CONCLUSIONS We present a case of IgG4-RD involving the thoracoabdominal aorta and retroperitoneum based on the 2019 classification criteria. The importance of radiological studies of IgG4-RD has increased, and F-18-FDG-PET/CT, which is a functional imaging modality of the whole body, is a valuable evaluation method for diagnosis and clinical outcomes.