Interstitial lung disease in inflammatory myopathies: clinical phenotypes and prognosis.

Interstitial lung disease (ILD) is a very important complication of the idiopathic inflammatory myositides (IIM), with a prevalence of approximately 40 %. Characteristic HRCT changes, most commonly NSIP, together with a restrictive ventilatory defect and an associated decline in DLco support the presence of ILD. The strongest risk factors are the presence of the anti-amino-acyl-tRNA synthetases (ARS) and anti-MDA-5 antibodies, but a raised index of suspicion for ILD should also apply to IIM patients of black ethnicity. Overall, the prognosis of ILD in IIM is good; between 50 and 66 % of cases have a stable disease course over a substantial period of time. The remaining proportion will show signs of worsening lung disease within 12 months of diagnosis. Whereas ARS antibodies and black ethnicity have no influence on ILD prognosis, detection of the anti-MDA-5 antibody carries a poor ILD outcome, in which hyperferritinaemia appears to be an important diagnostic and prognostic feature.