Outcomes in ankylosing spondylitis: what makes the assessment of treatment effects in ankylosing spondylitis different?

There are four major challenges in the assessment of outcomes in patients with ankylosing spondylitis (AS) that are particularly relevant to the evaluation of new therapies. Firstly, measures of symptoms and impairment in AS are not specific for inflammatory processes, they also capture mechanical symptoms and fixed limitations. The non-specific nature of these measures may cause them to be less responsive and therefore less useful in determining treatment efficacy. Secondly, acute phase reactants have limited value as measures of AS activity and other surrogate markers have not yet been established. Thirdly, the assessment of the disease modifying potential of new therapies is hampered by the slow rate of spinal fusion. Fourthly, work disability has not be studied as an endpoint in clinical trials in AS, despite the fact that work disability is an important outcome in patients with AS. Research into ways to overcome these challenges in outcome measurement will help identify useful therapies and define the range of outcomes that they influence.