Clinical significance of thyroid hormone and antibodies in patients with idiopathic interstitial pneumonia

Interstitial pneumonia is characterized by inflammation and excess deposition of the extracellular matrix in the pulmonary interstitium. There are some causes of interstitial pneumonia identified such as exposure to occupational dusts and organic substances, and connective tissue diseases (CTDs) are one of the main causes of interstitial pneumonia. However, the exact causes cannot be often identified, and the diagnosis of idiopathic interstitial pneumonia (IIP) is made for such cases. Although IIP is a heterogeneous group of interstitial pneumonia with unknown etiology, growing evidence suggests that IIP with autoimmune features which are not enough for the specific diagnosis of CTD are focused as a clinically distinct phenotype. Several definitions such as undifferentiated CTD (1), lung dominant CTD (2) and autoimmune featured interstitial lung disease (3) have been proposed by research groups for such cases, and the European Respiratory Society/American Thoracic Society Task Force put them together and proposed the tentative clinical entity “interstitial pneumonia with autoimmune features (IPAF)” in 2015 (4). These suggest that autoimmune features are important to identify the different clinical phenotypes among IIPs