Diffuse parenchymal lung disease

The diffuse parenchymal lung diseases (DPLDs) are a group of over 200 diverse conditions all of which affect either the alveolar space or the pulmonary interstitium. All DPLDs typically present with dyspnoea and diffuse infiltrates on chest X-ray. Achieving an exact diagnosis is frequently challenging and requires a careful history, detailed examination and assimilation of appropriate investigations. Key amongst these is high-resolution CT (HRCT) scanning. The recognition that many of the DPLDs have distinctive HRCT appearances has greatly reduced the need for lung biopsy. Understanding of the natural history of many of the DPLDs has also been greatly improved by insights derived from HRCT. Furthermore, novel treatments have been developed over the last decade and these may improve the outcome of many of the interstitial lung diseases. This article covers the key aspects to be considered in the history, examination and investigation of patients with suspected DPLD. Also covered is the classification of the idiopathic interstitial pneumonias with particular attention to pathogenesis, diagnosis and management and a brief summary of some rarer DPLDs.