Antibody predictors of mortality and lung function trends in myositis spectrum interstitial lung disease

Objectives The impact of autoantibody profiles on the prognosis for idiopathic inflammatory myositis-associated interstitial lung disease (IIM-ILD) and myositis spectrum ILD with myositis-specific antibodies (MSAs) remains unclear. This retrospective cohort study examined whether serological profiles were associated with mortality or longitudinal lung function change.Methods The baseline clinical/demographic characteristics and follow-up lung function data of consecutive adult patients with IIM-ILD or interstitial pneumonia with autoimmune features (IPAF) positive for MSAs (IPAF-MSA) were extracted from three hospitals. Univariate and multivariate Cox proportional hazards analyses were used to compare mortality between groups of patients with different autoantibodies. Regression models were used to analyse their lung function trends.Results Of the 430 included patients, 81% met the IIM criteria, and the remaining 19% were diagnosed with IPAF-MSA. On univariate analysis, the risk factors associated with mortality included higher age, Charlson Comorbidity Index, and CRP; and lower BMI, baseline TLCO% and FEV1%. Compared with anti-MDA5 negativity, anti-MDA5 positivity (MDA5+) was associated with higher mortality in the first 3 months [hazard ratio (HR) 65.2, 95% CI 14.1, 302.0], while no significant difference was seen thereafter (HR 0.55, 95% CI 0.14, 2.28). On multivariate analysis, combined anti-synthetase antibodies were associated with a reduced risk of mortality (HR 0.63), although individually, mortality was reduced in patients with anti-Jo1+ (HR 0.61, 95% CI 0.4-0.87) and increased in patients with anti-PL7+ (HR 2.07, 95% CI 1.44-2.99). Anti-MDA5+ was associated with slow improvement in %FVC over the first 3 years, while anti-PL7+ was linked with a slow decline from 12 months onwards.Conclusion Among the autoantibody profiles in myositis spectrum disorders, anti-MDA5+ and anti-PL7+ conferred higher mortality risks in patients with IIM-ILD. Survivors of an early peak of mortality in anti-MDA5+ disease appeared to have a favourable prognosis.