Histopathology
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There have been few reports on immunoglobulin-G4 (IgG4)-related interstitial pneumonia (IP), and its clinical features remain unclear. The objective of this study was to assess whether IP with marked IgG4-positive plasma cell infiltration without extrathoracic lesions of IgG4-related disease (RD) should be diagnosed as a subtype of IgG4-RD or a separate entity. ⋯ IP with marked IgG4-positive plasma cell infiltration without extrathoracic lesions of IgG4-RD had different pathological features from those of IgG4-RD, and it is appropriate to regard this as a separate entity.