Interstitial lung diseases (ILDs) are a group of >200 disease entities characterized by diffuse lung parenchymal abnormalities. ILDs can be classified into two major groups: (1) diseases associated with predominant inflammation and fibrosis, and (2) diseases with predominantly granulomatous reaction in interstitial or vascular areas (Table 136-1 Major Categories of Alveolar and Interstitial Inflammatory Lung Disease). ILDs are nonmalignant and noninfectious, and they are typically chronic. The differential diagnosis of ILDs often includes infections (e.g., atypical mycobacteria, fungi), congestive heart failure, and malignancy (e.g., bronchoalveolar cell carcinoma). One of the most common ILDs associated with a granulomatous reaction, sarcoidosis, is discussed in Chap. 169 Sarcoidosis. Other common ILDs include idiopathic pulmonary fibrosis (IPF) and ILDs related to connective tissue diseases. Many ILDs are of unknown etiology; however, some ILDs are known to be associated with specific environmental exposures including asbestos, radiation therapy, and organic dusts.
| APPROACH TO THE PATIENT | ||
Interstitial Lung DiseaseHistory: Common presenting symptoms for pts with ILDs include dyspnea and nonproductive cough. Hemoptysis is uncommon in ILDs and could suggest diffuse alveolar hemorrhage, lymphangioleiomyomatosis (LAM), or granulomatosis with polyangiitis (GPA), as well as a secondary pulmonary infection. Assessment for connective tissue disease symptoms (e.g., Raynaud's) should be performed. Symptom onset and duration can assist in the differential diagnosis. Chronic symptoms (over months to years) are typically seen in most ILDs, including IPF, pneumoconioses, connective tissue diseases, and pulmonary Langerhans cell histiocytosis (PLCH or eosinophilic granuloma). Subacute symptoms (over weeks to months) can also be observed in many ILDs, especially in sarcoidosis, drug-induced ILDs, and cryptogenic organizing pneumonitis (COP, also known as bronchiolitis obliterans with organizing pneumonia [BOOP]). Acute presentations are uncommon for ILDs but are typically observed with acute interstitial pneumonia (AIP), and they can also occur with eosinophilic pneumonia, GPA, and hypersensitivity pneumonitis (HP). Sudden onset of dyspnea can indicate a pneumothorax, which occurs in PLCH and tuberous sclerosis/LAM. Fatigue is common in all ILDs. Episodic presentations also are unusual, but they are more typical for eosinophilic pneumonia, HP, pulmonary hemorrhage, Churg-Strauss syndrome, and COP. Age at presentation also can guide the differential diagnosis. IPF pts typically present at age >60, while sarcoidosis, PLCH, LAM, and connective tissue disease-related ILD often present between the ages of 20 and 40. LAM occurs exclusively in women, while IPF and ILD in rheumatoid arthritis (RA) occur more often in men. Cigarette smoking is a risk factor for several ILDs including IPF, PLCH, Goodpasture syndrome, pulmonary alveolar proteinosis (PAP), and respiratory bronchiolitis/desquamative interstitial pneumonia. Occupational exposures and hobbies can be important risk factors for many types of HP as well as pneumoconioses. Previous medical treatment with radiation and drugs also should be assessed. Family history of ILD should be obtained; variants in MUC5B and telomerase pathway genes are associated with IPF. Physical examination: Bibasilar end-inspiratory crackles are commonly observed in inflammatory ILDs, but they are less frequent in granulomatous ILDs. Clubbing of the digits is observed in some pts with advanced ILD. Laboratory studies: Testing can suggest an underlying connective tissue disorders (e.g., anti-cyclic citrullinated peptide antibody for RA). Specific serum antibodies can confirm exposure to relevant antigens in HP, but they do not prove causation. Anti-GM-CSF antibodies are diagnostic of acquired PAP. Chest imaging: Chest x-ray (CXR) does not typically provide a specific diagnosis but often raises the possibility of ILD by demonstrating a bibasilar reticular pattern. Upper-lung-zone predominance of nodular opacities is noted in several ILDs, including PLCH, sarcoidosis, chronic HP, and silicosis. High-resolution chest CT scans provide improved sensitivity for the early detection of ILDs and may be sufficiently specific to allow a diagnosis to be made in ILDs such as IPF, PLCH, and asbestosis. Honeycombing is indicative of advanced fibrosis. Pulmonary function testing: Lung function measurements can assess the extent of pulmonary involvement in pts with ILD. Most ILDs produce a restrictive ventilatory defect with reduced total lung capacity. The forced expiratory volume in 1 s (FEV1) and forced vital capacity (FVC) are typically reduced, but the ratio of FEV1/FVC is usually normal to increased. Reduction in the diffusing capacity of the lung for carbon monoxide (DLCO) is commonly observed. Tissue and cellular examination: In order to provide a specific diagnosis and assess disease activity, lung biopsy is often required. Bronchoscopy with transbronchial biopsies can be diagnostic in some ILDs, including sarcoidosis and eosinophilic pneumonia. In addition, bronchoscopy can assist by excluding chronic infections or lymphangitic carcinomatosis. However, the more extensive tissue samples provided by surgically obtained lung biopsies, typically obtained by video-assisted thoracic surgery, are often required to establish a specific diagnosis. Evidence for diffuse end-stage disease, such as widespread honeycombing, or other major operative risks are relative contraindications to lung biopsy procedures. |