Diffuse parenchymal lung diseases consist of disorders of known causes (rheumatic disease, environmental or drug related) as well as disorders of unknown cause. The latter include IIPs, granulomatous lung disorders (eg, sarcoidosis), and other forms of interstitial lung disease including LAM, PLCH, and eosinophilic pneumonia. The interstitial pneumonias are further categorized as chronic fibrosing, acute or subacute fibrosing, or smoking-related. Lymphoid interstitial pneumonia is typically associated with other disease processes, such as rheumatic disease or immunosuppression; idiopathic lymphoid interstitial pneumonia is rare.