IgG4-related pulmonary disease: the protean impersonator?

IgG4-related disease is an immune-mediated fibro-inflammatory disease, characterised by distinct pathological features. An increasing number of clinical phenotypes are described, from single-organ disease to a multisystem disorder, which can present to a variety of different specialities. Recognition is key; its protean manifestations can mimic other inflammatory diseases, infection and malignancy. Here, we present three cases to highlight the importance of being familiar with this condition in its various forms.