Physical functioning is a key outcome in chronic diseases such as axial spondyloarthritis/ ankylosing spondylitis, and should be closely monitored. There is modest evidence to show that physical functional status in ankylosing spondylitis correlates independently with both radiographic damage and disease activity. However, findings regarding the efficacy of current therapies in preventing radiographic progression of ankylosing spondylitis are sparse, and of limited quality.
In this article, we evaluate the extent to which current pharmacologic therapies for ankylosing spondylitis delay radiographic progression. In order to assess the efficacy of these therapies, however, we must first understand the context of disease progression for ankylosing spondylitis, as assessed by radiographs.
Radiographic progression in ankylosing spondylitis is generally assessed via the mean modified Stoke Ankylosing Spondylitis Spinal Score (mSASSS). Measuring disease progression in ankylosing spondylitis is complicated by highly variable progression rates (even in the absence of immunosuppressants), slow-developing spinal lesions, and suboptimal study design.
Furthermore, syndesmophytes often do not develop until 5 years after baseline conventional radiographs. It is highly likely that therapies may have changed during such a prolonged interval; therefore, when attempting to determine whether current therapies slow radiographic progression, this prolonged interval introduces the possibility of confounding.
Some investigators have demonstrated that disease progression in ankylosing spondylitis is typically linear for cohorts of patients. However, individual patients frequently display nonlinear progression, which can occur at any time during their disease. This variation in individual disease courses manifests as wide standard deviations.
In one study, Ramiro et al found a standard deviation of 16.2 points, over 20% of the total mSASSS scale, when measuring radiographic progression. Similarly, Baraliakos et al found that while 43% of subjects were rapid progressors (showing a fourfold greater rate of progression than the mean), 25% of patients exhibited no progression (