Recent advances in interstitial lung disease research

The interstitial lung diseases are a diverse collection of disorders characterized by impaired gas exchange, restricted physiology on lung function testing, and diffuse parenchymal lung infiltrates on radiography. Although the interstitial lung diseases are many (Table 1), in routine clinical practice, the most commonly encountered in general internal medicine practice are sarcoidosis, idiopathic pulmonary fibrosis, and connective tissue disease-associated interstitial lung diseases. In immunocompromised patients, infection is the most common cause of diffuse lung infiltrates and must be ruled out before any attempt to treat with immune altering agents like corticosteroids. This review will focus on the more clinically significant recent advances in the broad field of interstitial lung disease research, with emphasis on the more common interstitial lung diseases occurring in immunocompetent hosts. Advances in the classification of idiopathic interstitial lung diseases Idiopathic pulmonary fibrosis (cryptogenic fibrosing alveolitis in the British literature), is one of the commonly encountered interstitial lung diseases, with an estimated prevalence of 5-20 per 100,000. Formerly, the term idiopathic pulmonary fibrosis was used to describe a variety of idiopathic interstitial pneumonias (listed in Table 1), characterized clinically by finger clubbing and bibasilar “velcro” crepitations on examination. It is now apparent that these findings are not specific, and may be associated with any of the idiopathic interstitial pneumonias listed in Table 1. Robert Vassallo MD Thoracic Diseases Research Unit and Division of Pulmonary, Critical Care and Internal Medicine, Mayo Clinic and Foundation, Rochester, USA Email: [email protected] A recent joint statement by the American Thoracic Society and the European Respiratory Society, recommended that the term idiopathic pulmonary fibrosis be restricted to patients with the histopathologic lesion of usual interstitial pneumonia (Table 1).1 These guidelines resulted from the demonstration by numerous groups that the prognosis of patients with the lesion of usual interstitial pneumonia is distinctly worse than other types of idiopathic interstitial pneumonia. The median survival of patients with usual interstitial pneumonia is 3-5 years, and response to corticosteroid therapy is uniformly poor. 5 In contrast, the other idiopathic interstitial pneumonias are frequently steroid-responsive, and most patients survive >10 years after diagnosis. As a result of these recent findings, it is recommended that definite diagnosis with lung biopsy be considered in all patients suspected of having an idiopathic interstitial pneumonia. Advances in Diagnostic Imaging: the High Resolution CT scan The chest high resolution CT scan (HRCT) emerged over the 1990s as an indispensable non-invasive diagnostic tool. Whereas conventional CT of the chest examines 7to 10-mm slices obtained at 10-mm intervals, HRCT examines 1.0to 1.5-mm slices at 10-mm intervals, illustrating lung parenchyma in much better detail than conventional CT. In patients with interstitial lung disease, a systematic analysis of HRCT patterns is very important, permitting a diagnostic accuracy ranging from 50 to 90% (in selected series comparing HRCT with histopathology), depending on disease entity, and the experience of the interpreting radiologist. Characteristic HRCT appearances have been described in sarcoidosis, idiopathic pulmonary fibrosis, pulmonary Langerhans’ cell Histiocytosis, pulmonary alveolar proteinosis, and lymphangioleiomyomatosis. In the appropriate clinical setting, a characteristic HRCT may enable a provisional diagnosis without resort to lung biopsy. HRCT is also useful to guide the selection of lung regions to biopsy when either bronchoscopic or surgical lung biopsy is planned. It is important to remember that the utility of HRCT in diagnosing interstitial lung disease is directly proportional to the degree of expertise of attending radiologists reading the scans. It is also essential to emphasize that confirmation of the diagnosis by histopathology remains essential prior to embarking on potentially toxic immunosuppressive trials, with the exception of those cases when the HRCT findings and clinical data are absolutely characteristic of the disease entity.