The Idiopathic Interstitial Pneumonias and Connective Tissue Disease-Associated Interstitial Lung Disease

The idiopathic interstitial pneumonias (IIP) are seven fibro-inflammatory interstitial lung diseases of unknown cause, grouped together because of potentially similar clinical features. Each of the seven has a distinct histologic pattern; however, these patterns are not specific to the IIP, and they provide a framework for defining interstitial lung disease (ILD) of known-cause, including ILD associated with underlying connective tissue disease (CTD). With the exception of respiratory bronchiolitis, the histologic patterns corresponding with the other six IIP can be found in association with CTD. Considering all CTD together, the pattern of non-specific interstitial pneumonia is most common. High-resolution computed tomography (HRCT) can hint at the histologic pattern, track changes over time, and assess response to therapy. The goal of this article is to review histologic patterns and HRCT findings of the IIP as they relate to CTD-associated ILD.