Does the hospitalized patient with unexplained dyspnea have interstitial lung disease (ILD)?
How and why should idiopathic pulmonary fibrosis (IPF) be differentiated from other forms of ILD?
What is an acute exacerbation of IPF, and how can it be discriminated from other causes of worsening in ILD?
When is bronchoscopy indicated in the diagnosis or evaluation of ILD?
When should a pulmonary consultation be requested for patients with ILD?
How can patients with high oxygen requirements be transitioned home?
The interstitial lung diseases (ILDs) are a heterogeneous group of disorders with the common feature of inflammatory or fibrotic injury to the lung parenchyma. Hence, these disorders are also described as the diffuse parenchymal lung diseases (DPLDs). There are numerous potential etiologies for ILD which can be broadly divided into five categories: idiopathic, drug/medication related, environmental/occupational, genetic/hereditary, and autoimmune associated (Table 241-1).
Table 241-1 Etiologies of Interstitial Lung Disease by Category |Favorite Table|Download (.pdf)
Table 241-1 Etiologies of Interstitial Lung Disease by Category
- Rheumatoid arthritis
- Systemic lupus erythematosis
- Sjorgren syndrome
- Bird fancier's lung
- Surfactant protein A and C deficiency
- Telomerase mutations
While considered rare, these diseases affect approximately 500,000 individuals in the United States each year and result in 40,000 deaths, comparable to the number of deaths from breast cancer. The exact epidemiology is difficult to determine as patients presenting with these diseases are sometimes misidentified as having more common disorders such as congestive heart failure or chronic obstructive pulmonary disease. Further the epidemiology varies based on the subtype of ILD. Thus, epidemiology is best considered in the context of the ILD subsets.
Classification and Presentation
Because of the diversity of diseases encompassed in ILD, the American Thoracic Society and European Respiratory Society developed a two-level classification system to facilitate the clinical evaluation of ILD (Figure 241-1). This system divides ILDs initially based on specific mechanisms of disease into disorders of known etiology, idiopathic interstitial pneumonia, granulomatous disease, and rare diseases. The idiopathic interstitial pneumonias (IIPs) are further classified in a second level based on histologic appearance. For the purpose of this discussion, we will focus primarily on the IIPs and mention several other ILDs of particular relevance to the hospitalist.
American Thoracic Society/European Respiratory Society classification of interstitial lung disease. DPLD, diffuse parenchymal lung disease; LAM, lymphangioleiomyomatosis; HX, histiocytosis X. (Adapted from American Thoracic Society/European Respiratory Society International Multidisciplinary Consensus Classification of the Idiopathic Interstitial Pneumonias. This joint statement of the American Thoracic Society [ATS], and the European Respiratory Society [ERS] was adopted by the ATS board of directors, June 2001 and by the ERS Executive Committee, ...