Abstract
OBJECTIVES: To investigate the relationship between smoking history and pack-year exposure on the rate of end-organ damage in systemic lupus erythematosus (SLE). METHODS: The SLE incident cohort included patients who met American College of Rheumatology (ACR) 1997 or SLE International Collaborating Clinics (SLICC) 2012 SLE criteria and had rheumatology encounters at a US academic institution (2008-16). The primary outcome was median time to SLICC/ACR damage index (SLICC/ACR-DI) increase or death. Main explanatory variables were smoking status and pack-years. Covariates included age, sex, race, ethnicity, receipt of Medicaid, neighborhood area deprivation index, and baseline SLE damage. Damage increase-free survival was evaluated by smoking status and pack-years using Kaplan-Meier and Cox proportional hazards methods. RESULTS: Patients of Black race and Medicaid recipients were more commonly current smokers (p's < 0.05). Former smokers were older and more likely to have late-onset SLE (54% versus 33% of never and 29% of current smokers, p = 0.001). Median time to SLICC/ACR-DI increase or death was earlier in current or former compared to never smokers (4.5 and 3.4 versus 9.0 yrs; p = 0.002). In multivariable models, the rate of damage accumulation was twice as fast in current smokers (HR 2.18; 1.33, 3.57) and smokers with a >10 pack-year history (HR 2.35; 1.15, 3.64) versus never smokers. CONCLUSIONS: In this incident SLE cohort, past or current smoking predicted new SLE damage 4-5 years earlier. After adjustment, current smokers and patients with a pack-year history of >10 years accumulated damage at twice the rate of never smokers.