Lung involvement in IgG4-related lymphoplasmacytic vasculitis and interstitial fibrosis: report of 3 cases and review of the literature.

There have been a few reports on lung diseases associated with an increased number of infiltrating IgG4-positive plasma cells or lung involvement of IgG4-related sclerosing disease, although their characteristic histologic features have not been well described. Herein, we present 3 cases of interstitial lung disease with common histology and abundant IgG4-positive cell infiltration. Patient 1, a 65-year-old man, was incidentally noted to have a nodular lesion in the left hilar region. In patient 2, a 78-year-old man with dyspnea on effort, computed tomography revealed multifocal consolidation adjacent to the pleura in both lower lobes. Patient 3, a 74-year-old man, underwent lung biopsy for right-sided pleural effusion of unknown etiology. The histologic findings of the 3 individuals were characterized by expansion of the interstitium by dense lymphoplasmacytic infiltrate with prominent vascular involvement, which was indistinguishable from grade 1 lesion of lymphomatoid granulomatosis (LYG-G1). In situ hybridization for Epstein-Barr virus-encoded small RNA (EBER) revealed few or no EBER-positive lymphocytes. Vascular involvement showed subendothelial lymphoplasmacytic infiltrate, including numerous IgG4-positive plasma cells. The percentages of IgG4-positive to IgG-positive plasma cells were 85%, 47%, 46%, respectively. Similar vascular lesions have been described in previous reports of lung complications in IgG4-related sclerosing diseases. Some of these lesions were diagnosed as LYG-G1 without EBER-positive cells. In conclusion, LYG-G1-like lesion characterized by lymphoplasmacytic vasculitis might be a characteristic feature of IgG4-related lung disease.