Imaging manifestations of IgG4-related disease

IgG4-related disease is a multisystem immune-mediated disorder associated with lesions manifesting an IgG4-rich plasma cell infiltrate and often raised serum IgG4 concentrations. The disease can mimic neoplastic, infective, and inflammatory processes due to features such as development of masses or organ enlargement. Prompt consideration of this diagnosis is essential to avoid unnecessary investigations and offer appropriate treatments, which can include steroids and other immunosuppressive agents. Although histology is typically diagnostic, imaging is critical to assess disease burden, determine biopsy targets, and evaluate response to treatment. Characteristic imaging features can also point towards the diagnosis in the absence of biopsy. This review highlights these features, as well as more atypical findings, grouped by organ or system. Differential diagnoses are emphasised. The full spectrum of imaging methods is discussed. Whole-body imaging with integrated 2-[¹⁸F]-fluoro-2-deoxy-d-glucose (FDG) positron-emission tomography (PET)/computed tomography (CT) has an evolving role in the detection of multi-organ involvement and subsequent follow-up.