015. WHEN UROLOGY MEETS RHEUMATOLOGY: IGG4-RELATED DISEASE AS A RARE CAUSE OF RETROPERITONEAL FIBROSIS AND PERIAORTITIS

Abstract

Background: IgG4-related disease is a chronic fibroinflammatory condition characterized by serum IgG4 elevation and tissue infiltration with IgG4 positive plasma cells. This can lead to pseudotumours and affect almost every organ. We report a case of a retroperitoneal fibrosis secondary to IgG4-related disease that illustrates the challenges in diagnosing and treating this rare condition. Methods: A previously well 51 year old woman presented with a three month history of left sided loin pain and intermittent fevers and sweats. She was not taking any regular medication apart from bimatoprost eye drops for ocular hypertension. Physical examination showed left renal angle tenderness and an aortic murmur. Results: The initial laboratory findings showed an elevated acute phase response (CRP 156 mg/l and ESR 32 mm/hr) and mild deterioration in renal function with a reduction of eGFR to 42 ml/min from a baseline of 80ml/min. Echocardiography was normal. CT imaging of her abdomen showed a subcapsular fluid collection around the left kidney and extensive retroperitoneal fibrosis with marked paraaortic soft tissue infiltration. Left ureteric obstruction led to subsequent perforation of the renal calyx into the pararenal tissues. Following urgent urological consultation a left retrograde JJ stent was placed with excellent symptomatic improvement. A review of the patient's history did not reveal any risk factors or precipitating medications for the development of retroperitoneal fibrosis. There was a possible risk of occupational exposure to TB. TB testing was subsequently negative. LDH was normal and immunology was negative for ANA and ANCA. Serum immunoglobulin levels were normal with a normal IgG4 subclass level of 0.88 g/L. PET/CT imaging confirmed extensive retroperitoneal fibrosis but did not show any evidence of malignancy, vasculitis or aortitis. Biopsy was arranged despite technical difficulty due to the anatomical site of the fibrosis. Histology showed fibrous connective tissue with aggregates of inflammatory cells with prominent plasma cells. Immunohistochemistry revealed strong cytoplasmic staining for IgG4 in at least half of the plasma cells present. She was commenced on 30mg of prednisolone daily with a slow weaning regime. Methotrexate was started at 15mg weekly. This led to a rapid reduction of her CRP to 6mg/l and complete resolution of symptoms. Follow up CT imaging is pending. Conclusion: IgG4-related disease is a complex multisystem condition that responds well to immunosuppressive therapy commonly used by rheumatologists. Retroperitoneal fibrosis and para-aortic infiltration are hallmarks of the disease. High clinical suspicion for IgG4-related disease is needed and requires tissue histology with specialist staining for IgG4; especially as serum IgG4 levels may be normal. The pathophysiology of IgG4 related disease remains incompletely understood. Further research is needed to evaluate underlying disease mechanisms as well as possible immunomodulatory treatment options such as rituximab therapy.