Interstitial lung disease in SLE: a 30-year population study

OBJECTIVES: To compare incidence, risk factors and outcomes for interstitial lung disease (ILD) between patients with SLE and controls. METHODS: We performed a population-level cohort study using state-wide longitudinal hospital data from Western Australia (WA) for patients with SLE (n = 1854, median age 40 years, 86% female) and matched hospitalized controls (n = 12107, median age 40 years, 88% female) over the period 1985-2014. We estimated ILD incidence rate (IR), determined independent risk factors for ILD using multivariate logistic regression and assessed outcomes including mortality rate (MR) and cause of death. Results presented as median, frequency, IR or MR per 1000 person years (PY) with 95% CIs and IR or MR ratios (IRR or MRR). RESULTS: ILD occurred in 3.8% of SLE patients with a higher IR in SLE than the controls (3.11, 95% CI 2.44-3.91 vs 0.12, 95% CI 0.08-0.16; IRR 26.8) that was stable over time. Time to ILD from index was shorter in SLE and risk factors for ILD included older age, smoking and serositis. SLE-ILD patients experienced higher MRs (MR 52.0, 95% CI 37.0-71.1) than both SLE patients without ILD (MR 17.7, 95% CI 16.0-19.6; MRR 2.94) and controls with ILD (MR 22.8, 95% CI 12.1-38.9; MRR 2.28). ILD decreased survival for SLE and control cohorts and respiratory causes of death predominated in both the ILD groups. CONCLUSION: ILD occurred more frequently in SLE than the controls with older age, smoking and serositis as risk factors. As SLE-ILD adversely impacts prognosis with increased mortality, greater awareness and earlier management is warranted.