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Diffuse parenchymal lung disease: an introduction 

Diffuse parenchymal lung disease: an introduction

Diffuse parenchymal lung disease: an introduction

A.U. Wells


A relevant case history from Oxford Case Histories in Respiratory Medicine has been added to this chapter.

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date: 24 April 2017

The nomenclature of diffuse parenchymal lung disease has caused a great deal of confusion, with use of complicated histopathological terms not always corresponding exactly to clinico-radiological entities.

‘Cryptogenic fibrosing alveolitis’—Hamman and Rich first described a presentation of rapidly progressive fatal diffuse parenchymal lung disease in which the cardinal histological features were interstitial inflammation and fibrosis. A typical clinical picture was defined, consisting of progressive dyspnoea, bilateral predominantly basal crackles on auscultation, reticulonodular predominantly basal abnormalities on chest radiography, and a restrictive ventilatory defect on lung function testing. This clinical entity was termed ‘cryptogenic fibrosing alveolitis’ (CFA) or ‘idiopathic pulmonary fibrosis’, but it has become clear that the outcome associated with this presentation—termed the ‘CFA clinical syndrome’—is highly heterogeneous.

Diffuse parenchymal lung diseases can be subdivided into five major groupings: (1) idiopathic interstitial pneumonias; (2) diseases associated with systemic conditions, including rheumatological disease; (3) diseases caused by environmental triggers or drug ingestion; (4) granulomatous diseases; and (5) other diffuse lung diseases.

Idiopathic interstitial pneumonias

Classification—this is based on recognition of clinical, radiological, and histopathological patterns, as opposed to the purely histopathological terminology. The following are recognized: (1) usual interstitial pneumonia (UIP); (2) nonspecific interstitial pneumonia (NSIP); (3) desquamative interstitial pneumonia (DIP); (4) respiratory bronchiolitis–interstitial lung disease (RBILD); (5) diffuse alveolar damage (DAD); (6) lymphocytic interstitial pneumonia (LIP); and (7) cryptogenic organizing pneumonia.

Diagnosis—is complicated by the large number of disorders grouped within the diffuse parenchymal lung diseases. A systematic diagnostic algorithm, based upon careful clinical evaluation and a logical sequence of tests, is essential. This approach can be broken down into two phases: (1) clinical history, clinical examination, chest radiography, pulmonary function tests, and selective blood tests; and (2) high-resolution CT, bronchoalveolar lavage (in some cases), and lung biopsy (in a few cases).

Clinical patterns of disease—the chronic diffuse parenchymal lung diseases can be broadly subclassified into five patterns of longitudinal disease behaviour, based upon cause, severity, the relative degree of inflammation and fibrosis, and observed change in the short term. Each clinical pattern is associated with a separate approach to management: 1 Self-limited inflammation—usually caused by an extrinsic agent, usually responds to withdrawal of an offending agent, and other therapy is unnecessary. 2 Stable fibrotic disease—most commonly encountered in sarcoidosis, following drug-induced lung disease, and in patients with formerly active rheumatological disorders. Treatment is not required, but monitoring of serial pulmonary function tests is needed. 3 Major inflammation, with or without supervening fibrosis—often a feature of drug-induced lung disease, and also of some patients with cryptogenic organizing pneumonia, DIP, hypersensitivity pneumonitis, sarcoidosis, and aggressive inflammatory disease in rheumatological disease. Treatment with corticosteroids is usual, initially at high dosage. 4 Slowly progressive fibrotic disease, in which stabilization is a realistic goal—frequently seen in sarcoidosis, hypersensitivity pneumonitis, rheumatological conditions, and in many patients with fibrotic NSIP. Aggressive initial treatment is usually warranted to ensure optimal control of disease activity. Long-term therapy is often required. 5 Inexorably progressive fibrotic disease—the hallmark of IPF, but an IPF-like course is sometimes observed in idiopathic fibrotic NSIP, rheumatological disease, and in a few patients with chronic hypersensitivity pneumonitis. Long-term treatment may slow disease progression, but initial high-dose therapy achieves nothing in known IPF and may cause unnecessary drug toxicity.

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