Interstitial Lung Disease: A Clinical Overview and General Approach
Commonly, interstitial lung disease (ILD) presents with dyspnea on exertion, diffuse bilateral infiltrates on chest imaging, and restriction with diffusion impairment on physiologic testing. When tissue is obtained, the lung parenchyma may contain any combination of abnormalities, including inflammation, fibrosis, and granulomas. While many forms of ILD are extremely rare, there are some, such as idiopathic pulmonary fibrosis (IPF) and sarcoidosis that are seen commonly in general pulmonary practice. Masqueraders of ILD such as infection, pulmonary edema, and malignancy will be encountered in the assessment of an abnormal chest radiograph, and distinguishing these from true ILD is crucial.
ILD refers to a heterogeneous collection of more than one hundred distinct lung disorders that tend to be grouped together because they share clinical, radiographic, and pathologic features. These disorders are sometimes called diffuse parenchymal lung disease (DPLD) to make the point that the interstitium is not the only compartment of the lung affected. Entities such as organizing pneumonia or pulmonary alveolar proteinosis may cause an alveolar filling process. Respiratory bronchiolitis and chronic hypersensitivity pneumonitis may center on the airway, involving this compartment as well. Occasionally, purely airway-centered diseases like bronchiolitis obliterans may be initially identified as an ILD because of overlapping radiographic findings. A structured approach is necessary since treatments may vary considerably depending on the diagnosis.
Diagnosis is based upon a comprehensive history, a careful physical examination, as well as review of laboratory data, physiologic studies, radiography, and in some cases, pathologic tissue obtained from lung biopsy. Multidisciplinary review is an important part of the process and can have a significant impact on diagnostic and management decisions. For each patient, decisions regarding diagnostic approach and therapy must be individualized based upon the patient’s respiratory status, comorbid medical conditions, and personal approach to medical care.
Diagnostic Approach to ILD
Several classification schemes for ILD have been proposed, which include histopathologic and clinical characteristics.1 The American Thoracic Society (ATS)/European Respiratory Society (ERS) consensus panel classification system was published in 2001 and has recently been revised.2 One approach is given in Figure 54-1.
An overview of ILD classification. DIP, desquamative interstitial pneumonia; RB-ILD, respiratory bronchiolitis interstitial lung disease; LCH, Langerhans cell histiocytosis; LAM, lymphangioleiomyomatosis; IPF, idiopathic pulmonary fibrosis; NSIP, nonspecific interstitial pneumonia; COP, cryptogenic organizing pneumonia; LIP, lymphocytic interstitial pneumonia; AIP, acute interstitial pneumonia. (Data from ATS/ERS classification, 2001.)
It is often helpful in the case of any individual patient to incorporate a combination of historical, clinical, radiographic, and pathologic features. Distinguishing those patients who have a known cause for their ILD (e.g., connective tissue disease, occupational or environmental exposure, or drug toxicity) from those who do not (e.g., IPF, sarcoidosis) is an important ...