Methotrexate and low-dose prednisone in idiopathic retroperitoneal fibrosis: a randomised clinical trial

Objectives: To test the efficacy and safety of methotrexate plus low-dose prednisone in patients with idiopathic retroperitoneal fibrosis. Methods: We conducted an open-label, randomised, active-controlled, non-inferiority phase III trial. Sixty (out of 78 screened) adults with newly diagnosed idiopathic retroperitoneal fibrosis and an estimated glomerular filtration rate >30 mL/min/1.73 m2 were enrolled at outpatient clinics of two Italian centres (Nephrology units of Parma University Hospital and Milano Policlinico Hospital). Patients were randomly assigned (1:1) to receive low-dose prednisone plus methotrexate (MTX + LowPred) or standard-dose prednisone alone (standPred) for nine months. The primary endpoint was remission at month 9. Remission was defined as absence of symptoms and ureteral obstruction (free of stents or nephrostomies), and normal acute-phase reactants; secondary endpoints included reduction in RPF thickness, relapses and treatment-related toxicity. Results: 29 patients received MTX + LowPred and 31 standPred. Twenty-six patients (89.7 %) receiving MTX + LowPred and 25 (80.6 %) receiving standPred achieved and maintained remission until month 9. The difference between remission rates was 9.1 % (95 %CI -9.9 %-27.3 %), meeting the criterion for non-inferiority. Time-to-remission was similar (log-rank test p = 0.549). The two groups showed comparable RPF thickness reduction and relapse rates. The median cumulative prednisone dose was significantly higher in the standPred group (p < 0.001). No significant differences in adverse events were observed. Conclusions: A low-dose prednisone plus methotrexate regimen is non-inferior to standard-dose prednisone in achieving remission in idiopathic retroperitoneal fibrosis, allowing significant reduction in glucocorticoid exposure. Trial registration: ClinicalTrials.gov: NCT01240850.