Pulmonary hypertension is common in severe diffuse parenchymal lung disease, resulting from hypoxemia and obliteration of small pulmonary vessels.
Clinical features
Patients with diffuse parenchymal lung disease most commonly have dyspnea as the presenting symptom. Dyspnea is noticed initially on exertion but, with severe disease, may be experienced even at rest. Cough, usually nonproductive, is also common. On physical examination, auscultation of the chest characteristically reveals dry crackles or rales, which often are most prominent on inspiration at the lung bases. However, the likelihood of hearing crackles depends on the particular diagnosis; for example, crackles are especially prominent in IPF and less frequent in sarcoidosis. Clubbing may be present, particularly with certain types of diffuse parenchymal lung disease. If cor pulmonale develops, cardiac physical findings may be associated with pulmonary hypertension and right ventricular hypertrophy.
Chest examination is often notable for inspiratory crackles, particularly at the lung bases.
Diagnostic approach
The chest radiograph is the most important means for making the initial macroscopic assessment of diffuse parenchymal lung disease. The characteristic radiographic picture of diffuse parenchymal involvement that primarily involves alveolar walls is described as either reticular (increased linear markings) or reticulonodular (increased linear and small nodular markings; see Fig. 3.6). The pattern has also previously been called an “interstitial pattern” because it was believed to reflect a process limited to the alveolar walls. However, histopathology often indicates that some of these processes extend into alveolar spaces as well. The absence of chest x-ray abnormalities does not exclude the presence of diffuse parenchymal disease; entirely normal chest radiographic findings have been reported in up to 10% of patients. The pattern on chest radiograph is not particularly useful for gauging the relative amounts of inflammation versus fibrosis, each of which may result in a similar pattern.
Reticular or reticulonodular changes are frequently diffuse throughout both lung fields, although individual causes of diffuse parenchymal lung disease may be more likely to result in either an upper or a lower lung field predominance of the abnormal markings. In addition to the reticular or reticulonodular pattern, certain diseases may reveal other associated findings on chest radiograph, such as hilar adenopathy or pleural disease. These additional features noted with some diseases are discussed in Chapters 10 and 11.
A reticular or reticulonodular pattern on chest radiograph is characteristic of many diffuse parenchymal lung diseases, but up to 10% of patients have normal radiographic findings.
With long-standing and severe disease, the lungs may become grossly distorted. In addition, regions of cyst formation between scarred and retracted areas of lung often occur (see Fig. 9.7). A corresponding pattern of honeycombing on chest radiograph may be apparent. Cor pulmonale may be suspected on chest radiograph by the presence of right ventricular enlargement, best appreciated on the lateral view (see Fig. 14.3).
HRCT of the chest is an important step in the evaluation of diffuse parenchymal lung disease (see Figs. 3.9 and 11.2). Because of the quality of images of the pulmonary parenchyma, early changes that are not evident on routine chest radiography often can be seen by HRCT. In addition, the specific pattern of
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abnormality on an HRCT scan may be suggestive of a particular underlying diagnosis such as IPF and may help to distinguish inflammation from fibrosis.
Bronchoalveolar lavage (BAL) is a relatively noninvasive procedure for sampling the cell population of the alveolitis. A flexible bronchoscope is placed as distally as possible into an airway, and an irrigation or lavage of normal saline through the bronchoscope enables collection of cells from the alveolar spaces. These cells are thought to be representative of the cell populations responsible for the alveolitis. Although this technique has been useful as a relatively noninvasive means of obtaining cells for research studies on diffuse parenchymal lung disease, its clinical usefulness for making a diagnosis or for sequential evaluation of disease activity is limited. Samples obtained by BAL in the evaluation of diffuse parenchymal lung disease are primarily useful for ruling out pulmonary hemorrhage or infection.
When a careful evaluation of the clinical, radiographic, laboratory, and pulmonary function findings does not allow the clinician to make a confident diagnosis, a lung biopsy is considered. A variety of biopsy procedures have been used to obtain tissue specimens from the lung, which are subjected to several routine staining techniques. The most frequently used biopsy procedures for this purpose are thoracoscopic lung biopsy and transbronchial biopsy (via flexible bronchoscopy). More recently, cryobiopsies with a bronchoscope, using a liquid cooling agent to freeze the tissue being biopsied, are being investigated as a means of obtaining larger, more useful specimens nonsurgically. Thoracoscopic biopsy often is the most appropriate procedure for obtaining a sufficiently large specimen of tissue for examination. However, when sarcoidosis (or several other specific forms of diffuse parenchymal disease) is suspected, transbronchial biopsy is a particularly suitable initial procedure because the characteristic pathology is present in tissue adjacent to the airways.
Findings on functional assessment of the patient with diffuse parenchymal lung disease were reviewed under Pathophysiology. Briefly, patients have a restrictive pattern on pulmonary function testing, with decreased lung volumes and preserved airflow. Diffusing capacity usually is reduced, which is indicative of loss of surface area for gas exchange. Hypoxemia is usually (although not necessarily) present, and PO2 falls even further with exercise. Hypercapnia is rarely a feature of the disease. When it occurs, hypercapnia usually reflects preterminal disease or an additional unrelated process.
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