Pulmonary manifestations of immunoglobulin G4-related sclerosing disease.

Immunoglobulin (Ig)G4-related sclerosing disease (ISD) (also called IgG4-related systemic disease, IgG4-related disease or hyper-IgG4 disease) is a recently described systemic fibroinflammatory disease associated with elevated circulating levels of IgG4. Although initial descriptions of this disorder focused on its pancreatic presentation (autoimmune pancreatitis), it has become apparent that ISD is a systemic disease with many facets. The lesion of ISD is characterised by lymphoplasmacytic inflammation, fibrosis, phlebitis and increased numbers of IgG4-positive plasma cells. The disease can either be localised to one or two organs, or be present with diffuse multi-organ disease. Furthermore, lesions in different organs can present simultaneously or metachronously. In the thorax, lesions associated with ISD have been described in the lung parenchyma, airways and pleura, as well as the mediastinum. Data published to date suggest that ISD may account for a portion of various fibroinflammatory conditions of unknown cause encountered in the chest, including inflammatory pseudotumours, idiopathic interstitial pneumonias, fibrosing mediastinitis, inflammatory pleural lesions and, occasionally, airway disease. Some aspects of pulmonary manifestations attributed to ISD remain controversial and additional studies are needed to clarify the relationship along with the increasing relevance of this disorder to pulmonary medicine.