Objective: Interstitial lung disease (ILD) is an important feature of idiopathic inflammatory myositis (IIM). Factors associated with its development and progression remain incompletely understood. The authors report ethnicity differences and lung function trends that characterize the predilection for and natural history of ILD in a group of British patients with IIM.
Methods: A 10-year retrospective analysis of patients with IIM at two hospitals was conducted. Demographic, clinico-radiological and laboratory features of cases with and without ILD were compared. Serial pulmonary function tests, including measurements of forced vital capacity, volume and diffusing capacity for carbon monoxide, were used to identify longitudinal patterns of lung disease.
Results: A total of 107 patients with IIM were identified. ILD was present in 37.4%, with non-specific interstitial pneumonia being the most common radiological pattern (75%). ILD was more common in IIM patients of Black ethnicity (OR 3.42), and in cases where ANA (OR 3.06) and anti-histidyl-tRNA synthetase (OR 3.2) antibodies were detected. In the ILD cohort, 50% deteriorated, defined as a drop in diffusing capacity of the lung for carbon monoxide by <15% or forced vital capacity <10% during the study period, occurring in all within a year of onset of ILD and significantly more frequently in those with a synchronous onset of IIM and ILD. Black ethnicity was not associated with poor lung function outcome.
Conclusion: In IIM, the risk of developing ILD is significantly higher in patients of Black ethnicity. Progressive lung damage occurs in an appreciable subgroup of patients with IIM-ILD, heralded by functional lung decline at 1 year despite systemic immunomodulatory treatment.