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IgG4-Related Retroperitoneal Fibrosis — RACP Adult Medicine MCQ

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ModerateGeneral Internal MedicineIgG4-Related Retroperitoneal FibrosisRACP Adult Medicine

A 65-year-old man presents with fatigue, weight loss, and a palpable abdominal mass. CT shows a large retroperitoneal soft tissue mass encasing the ureters and aorta, causing bilateral hydronephrosis. His creatinine is 450 µmol/L. IgG4 is markedly elevated. What is the most likely diagnosis?

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Correct answer: A — Metastatic disease

Retroperitoneal fibrosis with elevated IgG4 is consistent with IgG4-related disease. IgG4-RD is a fibroinflammatory condition that can affect almost any organ (pancreas – autoimmune pancreatitis, retroperitoneum, salivary glands, orbits, kidneys, aorta). The retroperitoneal mass encasing ureters and aorta is characteristic. Tissue biopsy showing storiform fibrosis, lymphoplasmacytic infiltrate with IgG4+ plasma cells confirms the diagnosis. Treatment with corticosteroids produces dramatic improvement. Ureteric stenting may be needed acutely for obstructive uropathy.

Reference: eTG – 2025 – Rheumatology; ACG – 2024 – IgG4-Related Disease Guidelines