Prognostic significance of 1-year pulmonary function changes in inflammatory myopathy-related interstitial lung disease

BACKGROUND: The prognostic value of pulmonary function test (PFT) trends in idiopathic inflammatory myopathy-related interstitial lung disease (IIM-ILD) remains unclear. We evaluated whether one-year changes in forced vital capacity (FVC) and diffusing capacity (DLCO) predict 10-year mortality and lung transplantation. METHODS: In a retrospective, single-center cohort of adults with IIM-ILD classified by autoantibody status and 2017 EULAR/ACR criteria, ILD was defined by high-resolution chest CT (HRCT). Inclusion required baseline and follow-up PFTs 6-18 months apart. Cox regression and Kaplan-Meier analyses assessed associations between PFT changes and survival. Multivariable models adjusted for age, sex, smoking, baseline FVC, and PFT timing. RESULTS: The most common IIM subset among 149 patients (mean age 50.5 ± 12.9 years, 63 % female) was anti-synthetase syndrome (73 %). Over mean 6.3-year follow-up, 41 (27.5 %) died and 6 (4.0 %) underwent transplantation. In multivariate analyses, absolute and relative FVC declines of ≥5% over one year were significantly associated with increased 10-year mortality (HR=2.78, CI 1.27-6.09, p = 0.01 and HR=2.37, CI 1.11-5.05, p = 0.025) . Larger FVC declines (≥10%/≥15 %) showed stronger mortality associations, whereas stable or improved FVC predicted better outcomes (HR=0.38, CI 0.18-0.82, p = 0.01). DLCO decline was not associated with survival. Kaplan-Meier analysis demonstrated worse survival with FVC decline≥5 % (p = 0.028). Survival did not differ by autoantibody subtype or HRCT pattern. CONCLUSION: Even modest FVC decline (≥5 %) over one year predicts mortality and transplant in IIM-ILD, while stabilization or improvement in FVC associates with improved survival and should be considered therapeutic goals. Routine FVC monitoring may support risk stratification, guide transplant referral, and serve as a trial endpoint.