Efficacy and safety of mycophenolate mofetil in preventing relapse of IgG4-related disease with re-elevation of serum IgG4 level during maintenance therapy: a protocol for a multicentre, randomised, double-blind, placebo-controlled study in China.

INTRODUCTION: IgG4-related disease is a chronic fibroinflammatory disease with multiorgan involvement. Glucocorticoids and/or immunosuppressants as well as rituximab are both first-line treatments in remission induction therapy. However, relapse is common during the maintenance period, particularly in patients with re-elevation of serum IgG4 level. This study aims to evaluate whether adding mycophenolate mofetil (MMF) during the maintenance phase for such patients can reduce the risk of disease flare. METHODS: This study is a multicentre, randomised, double-blind, placebo-controlled study. A total of 108 eligible patients with re-elevation of serum IgG4 level during maintenance therapy will be included in this study and randomised in a 1:1 ratio to receive add-on MMF 0.5 g one time per day or placebo for 52 weeks. The primary outcome is the proportion of patients experiencing relapse at week 52. Secondary outcomes include time-to-relapse, changes in disease activity and serum IgG4 level, stratified relapse rate according to the elevation level of IgG4. Analyses will follow the intention-to-treat principle. ETHICS AND DISSEMINATION: The study has been approved by the Ethics Committee of Peking Union Medical College Hospital, Chinese Academy of Medical Sciences (approval no. K3231). Written informed consent will be obtained from all participants before enrolment. Findings will be disseminated through peer-reviewed journals and conference presentations. TRIAL REGISTRATION NUMBER: NCT05974683.