Pulmonary involvement in IgG4-related disease can manifest in any intrathoracic compartment including the lung parenchyma, airways, lymph nodes, mediastinum, and pleura. Although most patients with IgG4-related lung disease have extrapulmonary manifestations, some patients present with isolated pulmonary disease and may be difficult to diagnose. Approximately one-half of those with IgG4-related lung disease have respiratory symptoms at presentation. The most common form of intrathoracic involvement is mediastinal and/or hilar lymphadenopathy. Parenchymal manifestations of IgG4-related lung disease include single or multiple rounded opacities and interstitial lung disease. Airway disease can cause airway narrowing and asthma-like symptoms. Aside from mediastinal lymphadenopathy, IgG4-related fibrosing mediastinitis has also been reported. Pleural manifestations include pleural masses and pleural effusions. These patterns of intrathoracic disease are best characterized by CT (including high-resolution images of the lung parenchyma). Diagnostic confirmation of IgG4-related lung disease may require bronchoscopic or surgical biopsy, partly depending on the site of involvement. Histopathologic findings associated with IgG4-related lung disease are similar to those seen in extrapulmonary organs, but characteristic storiform fibrosis is not as apparent in lung biopsies. IgG4-related lung disease generally responds well to corticosteroid therapy.
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