Interstitial pneumonia with autoimmune features that met the proposed diagnostic criteria for IgG4‐related respiratory disease

We held a multidisciplinary discussion (MDD) about a 61‐year‐old woman who had an interstitial lung disease (ILD) without extrathoracic lesions that met the classification criteria for interstitial pneumonia with autoimmune features (IPAF) and the proposed diagnostic criteria for immunoglobulin G4 (IgG4)‐related respiratory disease (IgG4‐RRD). Clinically, the marked progression of lung‐limited diffuse lesions was consistent with IPAF. Serum IgG4 and rheumatoid factor levels simultaneously increased and did not contribute to a diagnosis. Pathologically, the significant hyperplasia of lymphoid follicles was consistent with rheumatoid arthritis (RA)‐associated ILD. Pulmonary venous occlusions by intimal fibrosis and intimal thickening were not important because these occlusions are found in IgG4‐related lung disease (IgG4‐RLD) and also in IPAF or ILDs related to connective tissue diseases (CTDs). Radiologically, fibrosing shadows that remained in the lung periphery after treatment were compatible with RA‐associated chronic ILD. We concluded that the present case was IPAF that met the proposed diagnostic criteria for IgG4‐RRD.