ANA: antinuclear antibody, ANCA: antineutrophil cytoplasmic antibody, CHP: chronic hypersensitivity pneumonitis, COP: cryptogenic organizing pneumonia, CTD-ILD: connective tissue disease-associated interstitial lung disease, EP: eosinophilic pneumonia, F: female, GGO: ground glass opacities, HP: hypersensitivity pneumonitis, IPF: idiopathic pulmonary fibrosis, M: male, MP: mercaptpurine, MTX: methotrexate, NSIP: nonspecific interstitial pneumonia, OP: organizing pneumonia, PE: pulmonary embolus, PM/DM: polymyositis/dermatomyositis, RBILD/DIP: respiratory bronchiolitis-associated interstitial lung disease/desquamative interstitial pneumonia, SSA: SS-A antibody, and UIP: usual interstitial pneumonia. A staging system, originally proposed for ILD with systemic sclerosis, by Goh et al. . Patient had a mild elevation of serum SS-A (1.20 AI) but lacked sicca symptom and other symptoms suggestive of underlying autoimmune disease (i.e., arthralgia, digital fissuring/ulceration, and Raynaud’s phenomenon). Patients had positivity of serum ANCA but lacked clinical symptom suggestive of underlying systemic vasculitis (i.e., skin rash, alveolar haemorrhage, and glomerulonephritis). #We defined both radiological “definitive UIP pattern” and “probable UIP pattern” as “UIP pattern” in the present study.