Sick leave in patients with ankylosing spondylitis before and after anti-TNF therapy: a population-based cohort study

To study levels of sick leave and disability pension before and after TNF-antagonist therapy in AS patients.

Using the population-based South Swedish Arthritis Treatment Group register, we identified 139 AS patients (aged 18-58 years, 78% men), who between January 2002 and December 2008 started their first treatment with adalimumab, etanercept or infliximab. We linked data to the payment register by the Swedish Social Insurance Agency and calculated the proportion on sick leave in 30-day intervals from 12 months before treatment start until 12 months after. For each AS patient, we randomly selected four subjects from the general population matched for age, sex and area of residence.

One to 3 months before treatment, an average of 24% of AS patients were on sick leave. During the first 6 months after treatment start, this fraction dropped to 15%, and further declined to 12% at 12 months (P < 0.001). Comparing AS patients with the general population, the relative risk of being on sick leave 3 months before treatment, treatment start and 12 months after treatment start was 8.0 (95% CI 4.6, 13.9), 9.2 (95% CI 5.4, 15.7) and 4.0 (95% CI 2.1, 6.3), respectively. The decrease in sick leave was not substantially offset by changes in disability pension.

There is a decline in sick leave during the first 12 months after initiation of TNF-antagonist treatment in AS patients not explained by societal factors or secular trends. The proportion of AS patients on disability pension remained unchanged during the observation period.