Objective: In Ankylosing spondylitis (AS), chronic spinal inflammation is the main feature. The reported prevalence for VF is highly variable and long-term outcome data sparse. We compared VF prevalence and mortality in patients with AS compared to the population risk.
Methods: State-wide observational study using linked health data for 2,321 AS patients and 22,976 non-exposed controls presenting to West Australian hospital between 1980-2015. We estimated survival by Kaplan-Meier curves, hazard ratios by conditional Cox regression and odds ratios by logistic regression.
Results: Period prevalence for VF was 9.3% for AS patients (60% males, mean age 39±19) and 2.5% for controls (p<0.01). The age, gender and osteoporosis adjusted risk for VF was nearly tripled for AS patients (HR=2.84; 95%CI: 2.36, 3.43) with little change over decades. Survival was significantly lower in AS patient with VF compared to AS without VF at 5, 10 and 20-years (98% vs 95%, 81% vs 90%, 43% vs 79%) respectively (p<0.001), and the age, gender and osteoporosis adjusted risk for death was HR=1.57(95%CI: 1.57, 2.64). AS patients with VF had on average 4-years shorter survival compared to control population (79 vs 83 years, p<0.0001). As patients with VF were more likely to have sustained multiple VF (OR=2.53; 95%CI: 1.49, 4.28; age-gender adjusted).
Conclusion: AS patients have over triple the risk of VF. The long-term VF prevalence for AS was nearly 10%. There was little change over time despite better treatments being available. VF prevalence significantly reduces survival rates in AS patients compared to controls.