IgG4-related disease: a novel, important but easily missed condition.

Immunoglobulin G4-related disease (IgG4-RD) is a multisystem, fibroinflammatory condition unrecognised in medical science until the last decade. It is characterised by progressive scarring and dysfunction of affected organs and tissues including the pancreas, hepatobiliary tree, kidneys, salivary glands, retroperitoneum and lungs. The diagnosis is made with the presence of numerous IgG4 positive plasma cells within a histologically-distinct chronic inflammatory process; most patients also have elevated serum IgG4. Though early cases were all identified in Japan, subsequent reports clearly demonstrate that IgG4-RD exists worldwide. There are no data confirming the prevalence of IgG4-RD in the West but it is thought to be very rare. Limited awareness of the condition and its heterogeneous presentation frequently results in misdiagnosis. Prompt and correct diagnosis is critical, as a rapid reversal of even advanced disease is often seen with corticosteroid therapy. We present three cases that illustrate some of the typical features of this condition.