A Randomized Controlled Study of the Efficacy and Safety of Lenalidomide in the Treatment of Active IgG4-related Disease

Inclusion Criteria: 1. Patients aged between 18 and 75 years who meet the 2019 American College of Rheumatology/European League Against Rheumatism (ACR/EULAR) classification criteria for IgG4-RD； 2. Patients with active disease: For patients with initial treatment or relapse after drug withdrawal, active disease is defined as having an IgG4-RD Response Index (RI) of at least 2 points in at least one organ at the time of screening; for those experiencing relapse while on treatment, active disease is defined as having an IgG4-RD RI of at least 3 points in at least one organ at the time of screening； 3. Patients with the clinical subtype of proliferative IgG4-RD； 4. Patients who have no plans for pregnancy within the next 18 months and who agree to use reliable contraceptive measures during the study period； Exclusion Criteria: 1. IgG4-RD patients with only fibrotic features; 2. Absolute neutrophil count \<1.5×10\^9 /L or platelet count \<100×10\^9/L; 3. Creatinine clearance less than 60 ml/ min; 4. Liver function Child-Pugh grade B or above; 5. Chronic active infection requiring systemic treatment; 6. Diagnosed with malignant tumor in the past five years; 7. Patients with a history of thrombosis; 8. Using biological agents within six months; 9. Known to be allergic to lenalidomide or thalidomide; 10. Pregnant or lactating women; 11. Patients with any other medical conditions or for specific reasons judged by the investigator to be ineligible to participate in the study.