Connective tissue disease-associated interstitial pneumonia and idiopathic interstitial pneumonia: similarity and difference.

Interstitial lung diseases (ILDs) are increasingly recognized in patients with systemic diseases. Patients with early ILD changes may be asymptomatic. Features of ILD overlap among systemic diseases and with idiopathic variety. High-resolution computed tomography plays a central role in diagnosing ILDs. Imaging features are often nonspecific. Therapy- and complication-related lung changes would pose difficulty in diagnosing and classifying an ILD. Biology and prognosis of secondary ILDs may differ between different disease-related ILDs and idiopathic variety. Combination of clinical features, serological tests, pulmonary and extrapulmonary imaging findings, and pathology findings may help to diagnose ILDs.