The subject of diffuse parenchymal lung disease has been considered a difficult one for practicing pathologists. The reasons for this are diverse. Open lung biopsies (now performed by minimally invasive video-assisted techniques) are relatively rare, histologic findings can be nonspecific, there are pathologic sample limitations requiring radiologic correlation, and we have an incomplete knowledge of the natural history of several of the pathologic processes resulting in diffuse lung fibrosis.
This volume illustrates a wide range of interstitial lung diseases, with computed tomographic imaging correlation. The first entry in this volume is an overview of the major problems involving the diagnosis of interstitial lung disease, with some historical background in terminology and classification. The prototypic fibrotic lung disease, idiopathic pulmonary fibrosis, is presented next by Kokh et al, with a pathologic discussion of usual interstitial pneumonia correlated with imaging findings. Choi et al illustrate a case report and discussion of Hermansky-Pudlak syndrome, a rare cause of diffuse interstitial fibrosis, which was once thought to result in pathologic and imaging findings identical to idiopathic pulmonary fibrosis but is currently believed to have distinct pathologic and radiologic findings. Morais et al present several cases of acute lung injury, including idiopathic interstitial pneumonia (Hamman-Rich syndrome) and acute exacerbations of interstitial fibrosis. In the article of Morais et al, 1 patient with acute exacerbation presented with acute lung injury superimposed on nonspecific interstitial pneumonia, and another had a history of fibrotic lung disease with acute exacerbation months later
There are several articles that follow, which involve secondary causes of diffuse parenchymal lung disease. There are 2 entries that discuss lung disease associated with rheumatologic disorders. Collins et al present a patient with rheumatoid arthritis and discuss the differential diagnosis of rheumatoid lung disease, organizing pneumonia, and drug-induced pulmonary toxicity. Huebner et al present 2 patients with interstitial fibrosis associated with dermatomyositis-polymyositis, one of whom was positive for the anti–Jo-1 antibodies, suspected to increase the risk of lung disease in patients with rheumatologic disorders.
The final 3 articles in this volume are examples of diffuse pulmonary fibrosis with a specific cause, the result in imaging and pathologic patterns that differ from usual or nonspecific interstitial pneumonia. Goicochea et al present 2 patients with Langerhans cell histiocytosis. One patient had localized lung involvement (pulmonary Langerhans cell histiocytosis or PLCH). The other patient experienced systemic neoplastic Langerhans cell histiocytosis, with lung involvement that mimicked radiologically the primary reactive form of the disease. Xu et al discuss pulmonary sarcoidosis, one of the more common secondary forms of pulmonary fibrosis that results in end-stage lung disease requiring transplant. Finally, Fix et al present a case of radiation pneumonitis, an iatrogenic form of pulmonary fibrosis that differs pathologically and radiologically from the other entities discussed.