Elevated IgG4 levels in patients demonstrating sarcoidosis-like radiologic findings
One of the radiologic patterns associated with IgG4-related systemic disease was similar to that of pulmonary sarcoidosis. We analyzed whether suspected pulmonary sarcoidosis might include unrecognized IgG4-related systemic disease. The enrolled patients had bilateral hilar lymphadenopathy and/or lung nodules on chest computed tomography, used to diagnose the patients who could either be compatible with or suggested as having pulmonary sarcoidosis. The IgG4 levels were retrospectively measured. Bronchoalveolar lavage (BAL) was analyzed for the presence of IgG subclasses, and specimens were stained by an antibody to IgG4. We compared these data in the suspected sarcoidosis patients, with or without elevated serum IgG4, with the laboratory data and bronchoscopy results in patients with definite sarcoidosis. All enrolled patients were followed for over 5 years. The patients were classified as 49 definite and 44 suspected sarcoidosis patients. Eight patients, including 6 suspected sarcoidosis patients, had elevated abnormal levels of serum IgG4. The suspected sarcoidosis patients had significantly lower percentages of lymphocytes and IgG in the BAL. One suspected sarcoidosis patient had positive IgG4 staining in a lung specimen. The elevated serum IgG4 patients among the patients with suspected sarcoidosis showed significantly higher levels of BAL IgG4, IgG4/IgG, and IgG4/IgG3 compared with the levels of the normal serum IgG4 patients. The follow-up study revealed that 1 patient with elevated serum IgG4 was complicated with other organ failure caused by IgG4-related systemic disease, and Castleman disease was diagnosed in 2 patients. IgG4-related systemic disease was, therefore, identified among the patients with elevated serum IgG4.