AB1097 RETROPERITONEAL FIBROSIS- A SINGLE CENTER EXPERIENCE
Authors: Mert Oztas, Emir Cemre, Izzet Atun, Cetin Demirdag, Serdal Ugurlu
Journal: Annals of the Rheumatic Diseases (2019)

<h3>Background</h3> Idiopathic retroperitoneal fibrosis (iRPF) is a rare, chronic, progressive disorder of unknown etiology and characterized by the presence of inflammatory and fibrous retroperitoneal tissue that often encompasses the ureters or abdominal organs. <h3>Objectives</h3> We evaluated iRPF cases of a single institution cohort to describe the features of patients (pts) with iRPF. <h3>Methods</h3> Twenty-eight iRPF patients who were being followed in our outpatient clinic between 2009 and 2018 were reviewed retrospectively. The demographic characteristics, clinical and radiologic findings, medical and interventional therapies were retrospectively collected and reported. <h3>Results</h3> We evaluated the data of 28 patients (17M/11F). The mean age at the time of diagnosis was 53±10,57, median follow up was 46 (IQR:23-67) months. Fifteen (%50) patients were presented with abdominal-pain which was the most common initial complaint; 9 (32%) flank pain, 1 anuria, 1 nocturia, and 2 had nausea. Twenty-one patients had hydronephrosis (11 bilateral hydronephrosis, 5 right and 5 left hydronephrosis) at initial visit and one patient diagnosed while on temporary hemodialysis therapy. Laboratory tests showed that ESR was elevated in 15 of 23 cases in which it was available (65.2%), with a median value of 39 mm/h (IQR:17-88); CRP was elevated in 19 of 28 patients (68%), with median value 11 (IQR:5,5-46,5). Mean serum creatinine level was 1,14 mg/dl IQR (0,83-1,9). Tissue involvement was detected with computed tomography in 25 (89%) patients. The remaining 3 patients' Involvement was located with <sup>18</sup> F-fluorodeoxyglucose positron emission tomography (<sup>18</sup> F-FDG-PET).<sup> 18</sup> F-FDG-PET has been performed in 19 patients and 16 of them (84%) revealed tissue involvement of iRPF. Histopathological samples were available for further analysis in 8 cases and 5pts' findings were consistent with iRPF (storiform fibrosis and dense lymphoplasmacytic infiltration were observed) and of these 5 pts, 2 of them were classified as IgG4-related subtype. The remaining 3 pts were diagnosed with positive radiologic findings. Medical and interventional therapies are presented in Table 1. The mean initial oral prednisone dose was 45,5±13,8 mg/day. Prednisone was discontinued in 4 patients after remission and for the remaining 23 pts; 12 pts' prednisone was tapered &lt;5 mg/day at mean 9 (IQR:6,7-22,5) months. One patient diagnosed AML-M2 during the follow-up and had allogenic stem cell transplantation. Final median values of ESR and CRP were 10 mm/h (IQR:4,7-17,7) and 4,4 mg/l (1,9-7,7), respectively (p= 0.001 and p=0.002). Final median serum creatinine level was 1,03 (IQR:0,78-1,28) (p=0,2). Thirteen pts (%46) were treated successfully with Rituximab who were not responded initial prednisone therapy. Twenty-one pts had ureteral stents and 11 of them are stent free at the final visit. Two pts had ureteroysis but the procedure was failed in one patient. None of the pts was deceased on the follow-up. <h3>Conclusion</h3> Steroids are the mainstay treatment for iRPF and steroid resistant cases could be treated with rituximab rescue therapy. Prompt interventional approaches are valuable bridging therapies for pts who presented with hydronephrosis. Imaging modalities add great value on the diagnose of iRPF. <h3>Disclosure of Interests</h3> None declared