IgG4-related disease: a disease we probably often overlook.

IgG4-related disease (IgG4-RD) is an increasingly recognised entity characterised by tumefied lesions that can affect multiple organs. Awareness of IgG4-RD is important, as it has been shown to mimic other diseases and may result in irreversible organ damage if not treated. If suspected, immunostaining for IgG4-positive plasma cells is essential for diagnosis and revision of old biopsies may be necessary.