Comparison of pulmonary and small airways function between idiopathic inflammatory myopathies patients with and without interstitial lung disease

ObjectiveTo evaluate pulmonary and small airways function in patients with idiopathic inflammatory myopathies (IIM) and make comparisons between patients with and without interstitial lung disease (ILD). MethodsNewly diagnosed IIM patients with and without ILD determined by high resolution computed tomography were included in the study.Pulmonary and small airways function was assessed by spirometry, diffusing capacity for carbon monoxide (DLCO), body plethysmography, single and multiple breath nitrogen washout, impulse oscillometry and measurement of respiratory resistance by the interrupter technique (R int ) using the Q-box system.We used discrepancies between lung volumes measured by multiple breath nitrogen washout and body plethysmography to evaluate for small airways dysfunction. ResultsStudy cohort comprised of 26 IIM patients, 13 with and 13 without ILD.IIM-ILD patients presented more frequently with dyspnoea, fever, arthralgias and positive anti-synthetase antibodies, compared to IIM patients without ILD.Classic spirometric parameters and most lung physiology parameters assessing small airway function did not differ between the two groups.Predicted total lung capacity and residual volume (TLC N2WO , RV N2WO ) measured by multiple breath nitrogen washout and the TLC N2WO /TLC pleth ratio were significantly lower in IIM-ILD patients compared to those without ILD (mean: 111.1% vs. 153.4%,p=0.034, median: 171% vs. 210%, p=0.039 and median: 1.28 vs. 1.45, p=0.039, respectively).R int tended to be higher among p=0.053). Conclusion Discrepancies between lung volumes measured by multiple breath nitrogen washout and body plethysmography in IIM-ILDpatients indicate an early small airways dysfunction in these patients.