Prevalence and severity of interstitial lung disease in mixed connective tissue disease: a nationwide, cross-sectional study

Background Mixed connective tissue disease (MCTD) is an immune-mediated, systemic disorder of unknown cause. Objective To assess the prevalence, pattern and severity of interstitial lung disease (ILD) in a cross-sectional study of the nationwide, Norwegian MCTD cohort. Methods 126 patients with MCTD were systematically examined for ILD by high-resolution CT (HRCT), pulmonary function tests (PFT), 6 min walk test (6MWT) and by the New York Heart Association (NYHA) functional classification of dyspnoea. The extent and type of HRCT lung abnormalities were scored according to the CT criteria of ILD recommended by the Fleischner Society. Results All 126 patients were Caucasian, 75% women. At the time of the cross-sectional ILD study, the patients had a mean disease duration of 9.0 years. 52% of the patients had abnormal HRCT findings, most commonly reticular patterns consistent with lung fibrosis (35%). Lung fibrosis was quantified as minor in 7%, moderate in 9% and severe in 19% of the patients. Fibrosis was uniformly concentrated in the lower parts of the lungs and was not associated with smoking. Patients with severe lung fibrosis had lower PFT values, shorter 6MWT and a higher mean NYHA functional class. After a mean 4.2 years' follow-up, overall mortality was 7.9%. Mortality in patients with normal HRCT was 3.3%, as compared with 20.8% in patients with severe lung fibrosis (p<0.01). Conclusions Severe lung fibrosis is common in MCTD, has an impact on pulmonary function and overall physical capacity and is associated with increased mortality.