Key Clinical Questions
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?
How do you distinguish an acute exacerbation of IPF from other causes of worsening in ILD?
What are the indications for pulmonary consultation? For bronchoscopy in the diagnosis or evaluation of ILD?
When do you use newer antifibrotic agents in hospitalized patients with ILD?
How do you discharge patients with high oxygen requirements to 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. These disorders are also described as the diffuse parenchymal lung diseases. Numerous potential etiologies for ILD may be broadly divided into five categories: idiopathic, drug/medication related, environmental/occupational, genetic/hereditary and autoimmune associated (Table 233-1). 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 due to misidentification of patients as having more common disorders such as congestive heart failure or chronic obstructive pulmonary disease (COPD). The epidemiology varies based on the ILD subtype.
TABLE 233-1Etiologies of Interstitial Lung Disease (ILD) by Category |Favorite Table|Download (.pdf) TABLE 233-1 Etiologies of Interstitial Lung Disease (ILD) by Category
Systemic lupus erythematosis
Bird fancier’s lung
Mucin 5b (Muc5b) variant
Surfactant protein A&C deficiency
CLASSIFICATION AND COMMON PRESENTATION
The term ILD encompasses a diverse group of diseases. The American Thoracic Society and European Respiratory Society developed a two-level classification system to facilitate the clinical evaluation of ILD (Figure 233-1). This system divides ILDs initially based on specific mechanisms of disease into: disorders of known etiology, idiopathic interstitial pneumonias (IIPs), granulomatous diseases and rare diseases. The idiopathic interstitial pneumonias are further classified into a second level based on histologic appearance. We will focus primarily on the IIPs and mention several other ILDs of particular relevance to the hospitalist. A general approach to the diagnostic evaluation of suspected ILD is presented in Figure 233-2.
ATS/ERS Classification of Interstitial Lung Disease (Diffuse Parenchymal Lung Disease, DPLD). Adapted from An official American Thoracic Society/European Respiratory Society statement: Update of the international multidisciplinary classification of the idiopathic interstitial pneumonias. This updated joint statement of the American Thoracic Society (ATS), and the European Respiratory Society (ERS) was adopted by the ATS board of director the ERS Executive Committee in 2013. Am J Respir Crit Care Med. 2013;188(6):733-748.