This study has been designed as a 12-month, open-label randomized controlled clinical trial. The study aims to compare the efficacy and safety of two treatment strategies in IgG4-RD patients with superficial organ involvement: prednisone plus iguratimod and prednisone plus leflunomide.

60 IgG4-RD patients with superficial organ involvement are enrolled in this study and randomly divided into two groups at a 1:1 ratio: Patients in Group I are treated with prednisone (≤20 mg qd, or equivalent glucocorticoid, taper to ≤5mg in 3 months) and iguratimod (25 mg bid). Patients in Group II are treated with prednisone (≤20 mg qd, or equivalent glucocorticoid, taper to ≤5mg in 3 months ) and leflunomide (10-20 mg qd).All patients will be followed up for 12 months, and clinical evaluations, laboratory tests, image examinations and IgG4-RD responder index (RI) will be recorded during follow up. The primary endpoint is the difference of relapse rate between two groups at 12 months. The secondary endpoints are relapse time, response rate and side effects.

Inclusion Criteria:

• 1. Fulfillment of the 2019 American College of Rheumatology/European League against Rheumatology (ACR/EULAR) IgG4-related disease classification criteria; 2. Newly-onset or relapsed patients who requires initiation or continuation of glucocorticoids treatment; 3. The addition of glucocorticoids was started at lower than 10 mg/d.

Exclusion Criteria:

• 1. Patients who were diagnosed as other autoimmune diseases; 2. Patients who were diagnosed as malignant diseases; 3. Pregnant and lactating women； 4. Active infection: HIV, HCV, HBV, TB； 5. Severe irreversible damage of organ function; 6. Receipt of any biologic therapy or immunosuppressive agent other than GCs.