Recurrent anterior uveitis and subsequent incidence of ankylosing spondylitis: a nationwide cohort study from 2002 to 2013

Background: Anterior uveitis is the most common extra-articular manifestation of ankylosing spondylitis (AS). AS-related anterior uveitis frequently presents as acute, recurrent iridocyclitis; therefore, AS is often initially suspected by an ophthalmologist, not by a rheumatologist. In this study, we aimed to investigate the relationship between the recurrence of anterior uveitis and the subsequent incidence of AS. Methods: From a national sample cohort, 10,483 patients with new-onset uveitis between 2004 and 2013 and 52415 matched control subjects who had never experienced uveitis were selected. Among the patients with new-onset uveitis, a subpopulation of patients with recurrent uveitis, defined as a minimum 120-day reported interval between consecutive claims of uveitis (based on diagnostic codes) treated with local or systemic steroids or immune-modulating drugs, was identified. The incidence rates of AS were calculated according to the number of episodes of uveitis, and the incidence rate ratios (IRRs) were derived on the basis of the incidence rate in the control group. Results: The incidence rate per 100,000 person-years of AS after the first uveitis episode was 121.5, whereas the incidence in the control group was 16.9 (IRR, 7.40; 95% CI, 4.99-10.98); after the second uveitis episode, the IRR increased to 17.71 (95% CI, 10.44-30.06). In male and female patients with recurrent uveitis, the incidence rates of AS were 284.1 and 268.7 per 100,000 person-years, respectively. In patients aged under 40 years, the IRR of the recurrent uveitis group was 46.78 (95% CI, 19.61-111.61). In patients aged over 59 years, AS incidence in the recurrent uveitis group did not differ from that in the control group. Conclusions: The risk of subsequent AS increased with the number of episodes of anterior uveitis. This quantitative evidence could contribute to the establishment of a rationale for ancillary workup for possible systemic associations in patients with recurrent uveitis.