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Background IgG4-related disease (IgG4RD) is a recently recognized disease entity. Differentiating IgG4RD from plasma cell type Castleman's disease (PCD) is important but also difficult using only pathological findings. In addition, little is known about the association between these two diseases with diffuse parenchymal lung involvement. Methods We analyzed the serum IgG4 levels and the ratio of IgG4/IgG-positive plasmacytes in the lung and lymph node specimens of eight patients previously pathologically diagnosed of PCD with diffuse parenchymal lung involvement (DL-PCD). We also compared the clinical and laboratory findings observed in these patients. Results Six of the eight patients exhibited abundant IgG4-positive plasmacytes in the lung and lymph node tissues and elevated serum IgG4 levels, thereby fulfilling the diagnostic criteria of IgG4RD with DL (DL-IgG4RD) in addition to having obstructive phlebitis and massive lymphoplasmacytic infiltration with fibrosis. However, three of these six patients exhibited higher levels of serum interleukin-6 and were still diagnosed with DL-PCD. Accordingly, three of these eight patients were considered as IgG4RD with DL (DL-IgG4RD), and the other five patients were ultimately given a diagnosis of DL-PCD. These two diseases have different characteristics in terms of age, symptoms, serum levels of C-reactive protein, and IgA, complicating allergic disorders, response to corticosteroids, and prognosis. Conclusions This is the first report to show a high prevalence of DL-IgG4RD in DL-PCD patients, although additional large investigations are necessary. Clinical and laboratory findings are important for distinguishing between these two diseases in other organs, as previously described., Author(s): Takaaki Ogoshi[sup.1] [sup.2] , Takashi Kido[sup.1] , Kazuhiro Yatera[sup.1] , Keishi Oda[sup.1] , Toshinori Kawanami[sup.1] , Hiroshi Ishimoto[sup.1] , Noriho Sakamoto[sup.3] , Arisa Sano[sup.4] , Chiharu Yoshii[sup.5] , Shohei [...]

Background IgG4-related disease (IgG4RD) is a recently recognized disease entity. Differentiating IgG4RD from plasma cell type Castleman's disease (PCD) is important but also difficult using only pathological findings. In addition, little is known about the association between these two diseases with diffuse parenchymal lung involvement. Methods We analyzed the serum IgG4 levels and the ratio of IgG4/IgG-positive plasmacytes in the lung and lymph node specimens of eight patients previously pathologically diagnosed of PCD with diffuse parenchymal lung involvement (DL-PCD). We also compared the clinical and laboratory findings observed in these patients. Results Six of the eight patients exhibited abundant IgG4-positive plasmacytes in the lung and lymph node tissues and elevated serum IgG4 levels, thereby fulfilling the diagnostic criteria of IgG4RD with DL (DL-IgG4RD) in addition to having obstructive phlebitis and massive lymphoplasmacytic infiltration with fibrosis. However, three of these six patients exhibited higher levels of serum interleukin-6 and were still diagnosed with DL-PCD. Accordingly, three of these eight patients were considered as IgG4RD with DL (DL-IgG4RD), and the other five patients were ultimately given a diagnosis of DL-PCD. These two diseases have different characteristics in terms of age, symptoms, serum levels of C-reactive protein, and IgA, complicating allergic disorders, response to corticosteroids, and prognosis. Conclusions This is the first report to show a high prevalence of DL-IgG4RD in DL-PCD patients, although additional large investigations are necessary. Clinical and laboratory findings are important for distinguishing between these two diseases in other organs, as previously described. Keywords Diffuse parenchymal lung disease * ImmunoglobulinG4-related disease * IgG4-related lung disease * Plasma cell type Castleman's disease, Introduction IgG4-related disease (IgG4RD) is a recently described systemic fibroinflammatory disease that is associated with elevated circulating levels of IgG4 [1, 2]. IgG4RD is clinically characterized by the enlargement of [...]