RecruitingPhase 2Drug trialA Study of Efgartigimod in Patients With IgG4-Related DiseaseThe goal of this clinical trial is to learn if efgartigimod can treat IgG4-related disease in adults. The main questions it aims to answer are: In patients with IgG4-related disease, does treatment with efgartigimod reduce the volume of the: * lacrimal gland(s) and/or * salivary gland(s) and/or * pancreas Participants will: * Receive efgartigimod once weekly for up to 12 weeks * Visit the clinic every one to six weeks for checkups and tests * Be asked to complete questionnaires to see how they feel on efgartigimod