Existence of "IgG4-related pleuritis" and its clinical features

Background: IgG4-related disease is a multi-organ affecting disease characterized by fibroinflammatory lesions with abundant IgG4-positive plasma cell infiltration and elevation of serum IgG4 levels. We recently experienced a few cases of idiopathic pleuritis with serum IgG4 elevation. However, it is unknown whether “IgG4-related pleuritis” exists; if so, what clinical features it has. Methods: To determine frequency of pleuritis with IgG4 elevation (>100mg/dl), we screened consecutive 350 patients who received IgG4 measurement. To clarify clinical features of pleuritis with IgG4 elevation, medical records of the patients were reviewed retrospectively. Results: Among 350 patients, 42 case of pleuritis and 86 cases of serum IgG4 elevation were found. Among 42 patients with pleuritis, 9 cases showed IgG4 elevation. Clinical features of 11 pleuritis patients with IgG4 elevation including additional 2 cases were analyzed. The cases were 8 male, mean ages was 72.6 year, and 3 and 2 of them had rheumatic diseases and cancer, respectively. Pleural effusions were exudative with abundant lymphocytes. In samples by pleural biopsy, lymphplasmacytic infiltration was found in 80% and IgG4 positive cell infiltration was detected in 4 out of 6 examined cases. All patients with pleuritis had only pleural inflammation, but no fibroinflammatory lesions. Glucocorticoid was effective on pleuritis. Conclusion: There exists “IgG4-related pleuritis” with pleural IgG4 positive plasma cell infiltration and elevated serum IgG4 levels. “IgG4-related pleuritis” is a distinct subtype of diseases with serum IgG4 elevation, characterized by glucocorticoid responsive pleura restricted inflammation without fibroinflammatory lesions.