Orphan Lung Diseases.

There are hundreds of rare orphan lung diseases. We have highlighted five of them, one from each of the five major categories of pulmonary disorders: pleuroparenchymal fibroelastosis (a rare diffuse parenchymal lung disease), pulmonary alveolar proteinosis (a rare autoimmune and diffuse parenchymal lung disease), lymphangioleiomyomatosis (a rare cystic lung disease), yellow nail syndrome (a rare pleural disease), and Mounier-Kuhn syndrome (a rare airway disorder). The pathogenesis, clinical presentation, diagnostic criteria, treatment options, and prognosis of each disorder is discussed. This review is by no means exhaustive and further research is needed to improve our understanding of these disorders.