Background Acute anterior uveitis (AAU) is the most common extra-articular manifestation in patients with ankylosing spondylitis (AS), developing in 20-30% of these patients during the course of their disease.

Objectives Our aim was to study the characteristics and risk factors associated with AAU in our cohort of AS patients.

Methods From our longitudinal observational cohort, 716 patients with AS (meeting modified New York Criteria) and at least 2 years follow up were included and who were followed from January 2006 to November 2013. Patients with (AAU+) and without (AAU-) uveitis were compared. Uveitis flare rates were calculated per year. T-test, Chi-squared tests and logistic regression were used where appropriate.

Results Of the 716 patients, 225 (31.4%) had a reported diagnosis of AAU at their baseline clinic visit. Patients with AAU+ were older compared to the AAU- group (mean age of 42.6 vs 37.9 years; p<0.001). AAU started after the onset of back pain in the majority of patients with only 10.5% of patients reporting onset of AAU before onset of AS related back pain. Patients with AAU had higher HLA-B27 (B27) prevalence (91.8% vs 82.1%, p<0.05). In the multivariate analysis (MVA), AAU was independently associated with age, B27, psoriasis, IBD and elevated CRP. B27 (OR=2.66 [95% CI=1.44-4.9]), psoriasis (OR=2.36 [95% CI=1.41-3.97]) and IBD (OR=2.25 [95% CI=1.27-4]) are the strongest independent predictors of AAU. Within the AS/IBD group (n=86), 43% of these patients had a history of AAU, of which 81% were B27 positive.

In patients with AAU, there was a trend towards more peripheral arthritis and enthesitis. The BASMI score was higher in patients with AAU (3.3 vs 2.7, P<0.05), however there was no association found on MVA. There was no significant difference found between the two groups in terms of BASDAI score, hypertension, diabetes, previous history of myocardial infarctions and smoking history.

There was no difference found between NSAID use at baseline (66.1% vs. 66.5%, p=0.90). Patients with AAU were more frequently treated with DMARDs (26% vs. 16.5%, p<0.01). Sulfasalazine was used more frequently in the AAU+ group (14.2% vs. 7.9%, p<0.01). Use of biologics was similar at baseline (22.2% vs. 18.4%, p=0.23).

Conclusions In our cohort of AS patients, an increased frequency of HLA-B27 was seen in AAU+ AS. AAU+ AS is associated with psoriasis and IBD. The psoriasis and IBD association is independent of HLA-B27, suggesting an interaction of other genetic as well as environmental factors. At baseline DMARD use was associated with AAU, likely reflecting the association with peripheral joint disease.

Disclosure of Interest None declared