Background: Idiopathic retroperitoneal fibrosis (iRPF) is a rare chronic fibro-inflammatory disorder of unknown etiology. Activated T-helper cells, which shed soluble interleukin-2 receptor (sIL-2R... Show moreBackground: Idiopathic retroperitoneal fibrosis (iRPF) is a rare chronic fibro-inflammatory disorder of unknown etiology. Activated T-helper cells, which shed soluble interleukin-2 receptor (sIL-2R) into the circulation, may play a pathogenetic role. Hence, measuring sIL-2R may be of value in monitoring disease activity and treatment response in iRPF patients. Methods: We performed a prospective inception cohort study of 82 patients with untreated (re)active iRPF stratified by elevated (> 623 U/mL) or normal sIL-2R level at baseline and compared disease characteristics among these groups. Baseline and changes in sIL-2R levels following treatment with tamoxifen (TMX) or prednisone (PDN) were analyzed and related to treatment response. Results: Median sIL-2R level was 668 U/mL (IQR 502.8-827.5); 48 patients (59%) had elevated baseline sIL-2R levels. Patients with elevated sIL-2R presented with higher CRP (P = 0.049) and serum creatinine (sCr) levels (P < 0.001) and more often had hydroureteronephrosis (P = 0.01). There was an age and sex adjusted linear association between baseline sIL-2R and both CRP (P = 0.02) and sCr (P < 0.001). Baseline and serial levels of sIL-2R were predictive and concordant, respectively, with clinical response in patients treated with PDN. ROC curve analyses of sIL-2R on a continuous scale and PDN treatment success showed an AUC of 0.84. A serum sIL-2R cut-off value for PDN treatment success of <= 703 U/mL was found with a sensitivity of 100% and specificity of 72%. Conclusion: Serial measurement of sIL-2R may be of value in monitoring disease activity and PDN treatment response in iRPF patients. Show less
