Interstitial lung disease in connective tissue diseases: evolving concepts of pathogenesis and management

The term interstitial lung disease (ILD) is used to describe a heterogeneous group of parenchymal lung disorders that share common radiologic, pathologic, and clinical manifestations. ILD in its various guises can be asymptomatic but detected by high-resolution computed tomography (HRCT) of the chest or by pulmonary function tests. The fibrosing forms of ILD are often incurable, and are associated with significant morbidity and mortality.ILD is subdivided into idiopathic interstitial pneumonia, of which idiopathic pulmonary fibrosis (IPF) is one subset, and diffuse parenchymal lung diseases, which may be secondary to a variety of occupational or environmental exposures, or - as discussed in the present review - can complicate multiple rheumatic or connective tissue diseases (CTDs). These diseases include systemic sclerosis (SSc), where ILD occurs in a majority of patients, and rheumatoid arthritis (RA), polymyositis/dermatomyositis (PM/DM), Sj？gren's syndrome, systemic lupus erythematosus (SLE), undifferentiated CTD, and mixed CTD, where ILD is a less frequent complication (Table 1). In addition to ILD, other forms of lung damage involving the pleura, vasculature, airways, and lymphatic tissues can complicate CTDs. These complications will not be covered in the present review.The frequency of ILD in CTDs varies based on patient selection and the methods used for detection. In general, the prevalence appears to be higher than previously thought. The clinical presentation is variable, ranging from cough to pleuritic pain and progressive shortness of breath. In some patients, ILD may be the presenting feature that predates the rheumatic disease, while in others the rheumatic symptoms predate ILD. Early recognition of pulmonary involvement in these patients is important for initiating appropriate therapy.Multidisciplinary combined connective tissue disease-associated interstitial lung disease (CTD-ILD) clinics with rheumatologists and respiratory specialists are being e