Study of Sirolimus in Idiopathic Retroperitoneal Fibrosis

Inclusion Criteria: 1. Idiopathic retroperitoneal fibrosis diagnosed on CT or MRI. For patients with suspected secondary retroperitoneal fibrosis or atypical idiopathic retroperitoneal fibrosis suggested by imaging, idiopathic retroperitoneal fibrosis should be confirmed by puncture biopsy 2. Increased ESR and CRP levels caused by this disease and/or active lesions suggested on imaging Exclusion Criteria: 1. Secondary retroperitoneal fibrosis 2. Having used corticosteroid (equivalent to \>10 mg per day of prednisone), immunosuppressant, or biologic within 3 months prior to enrollment 3. Having any contraindication of prednisone or sirolimus, or allergy to sirolimus, or having experienced serious adverse reactions from the previous use of any of the above drugs 4. Massive proteinuria (24-hour urine protein quantitation ≥3 g), moderate-to-severe anemia (hemoglobin \<90 g/L), agranulocytosis (white blood cell count \<1.5×10\^9/L or neutrophil count \<0.5×10\^9/L), platelet count \<50×10\^9/L, interstitial pneumonia 5. Uncontrollable diabetes, hypertension, hyperlipidemia, infection, or heart failure, or other serious complications 6. Malignancy 7. Pregnancy or need for pregnancy in the near future 8. Unable to adhere to follow-up or refuses to provide consent