Diffuse lung disease in patients with autoimmune disease is complex and requires accurate characterization during clinical evaluation, pulmonary function test interpretation, and imaging evaluation. Chest radiography and computed tomography (CT) are the mainstays of lung evaluation in these patients, and this imaging occurs in a variety of clinical settings. Some patients with autoimmune diseases are at especially high risk for lung disease, and in these cases screening or baseline imaging may be indicated. Some patients with autoimmune disease may present acutely with respiratory symptoms requiring urgent imaging, in which case acute lung injury must be differentiated from background lung disease. Finally, patients with suspected or established chronic fibrosing lung disease will be diagnosed or surveilled with lung imaging.

This work will focus primarily on chronic lung disease in patients with autoimmune disease. However, it is important to first acknowledge that imaging manifestations of acute lung injury from infectious disease may be indistinguishable from acute acceleration of inflammation or fibrosis. Therefore, in the acute setting, temporal evolution of imaging findings may be the only discriminator.

Asymptomatic patients with autoimmune disease may develop subtle or mild imaging findings of lung fibrosis, often termed interstitial lung abnormality. Some chronic, diffuse lung diseases in patients with autoimmune disease may not be purely interstitial, such as pulmonary alveolar hemorrhage or granulomatous processes. For these reasons, the term “interstitial lung disease” may in some cases be misleading or misapplied, and the more appropriate terminology may be “diffuse lung disease” or when irrefutable imaging signs of fibrosis are present, “chronic fibrosing lung disease.” However, in keeping with general clinical practice, and while keeping these caveats in mind, we will refer to imaging manifestations of chronic fibrosing lung disease with or without inflammation as interstitial lung disease (ILD).

To better understand imaging in ILD, we will begin with the individual imaging findings of lung fibrosis across radiography and CT. We will use a few specific autoimmune diseases such as the idiopathic inflammatory myopathies as illustrative examples of ILD. Finally, we will include more rare entities of lung fibrosis in autoimmune patients, such as pleuroparenchymal fibroelastosis.