Progression of Nonradiographic Axial Spondyloarthritis to Ankylosing Spondylitis: A Population‐Based Cohort Study

Abstract

Objective The long-term outcome of patients with non-radiographic axial spondyloarthritis (nr-axSpA) is unclear, particularly whether few or most progress to ankylosing spondylitis (AS). Our objective was to examine the progression to AS in a population-based inception cohort of patients with nr-axSpA. Methods The Rochester Epidemiology Project (REP) is a longstanding population-based study of health in the residents of Olmsted County, Minnesota. We searched the REP from 1985 to 2010 using diagnostic and procedural codes for back pain, HLA-B27 and pelvis magnetic resonance imaging, and performed detailed chart review to identify subjects who fulfilled the Assessment of Spondyloarthritis International Society classification criteria for axSpA but did not have AS. We followed these subjects from disease onset to March 15th, 2015, and used survival analysis to measure time to progression to AS. Results After screening 2151 patients, we identified 83 subjects with new-onset nr-axSpA. Over a mean follow-up of 10.6 years, 16 subjects progressed to AS. The probabilities of remaining as nr-axSpA at 5, 10, and 15 years were 93.6%, 82.7%, and 73.6%, respectively. Subjects in the imaging arm (n=18) progressed more frequently and rapidly than those in the clinical arm (n=65) (28% versus 17%; hazard ratio 3.50, 95% CI 1.15–10.6, p=0.02). Conclusions A minority (26%) of patients with nr-axSpA progressed to AS when followed for up to 15 years. This suggests that the classification criteria for nr-axSpA identifies many patients unlikely to progress to AS, or that nr-axSpA is a prolonged prodromal state, requiring longer follow-up to evolve to AS.

Rate and Predisposing Factors for Sacroiliac Joint Radiographic Progression After a Two‐Year Follow‐up Period in Recent‐Onset Spondyloarthritis

“…The findings of the present study (a low rate of progression after a 2‐year follow‐up period) do not confirm the usual 10% rate (i.e., 10% of patients with nonradiographic structural damage will switch to radiographic structural damage after 2 years of follow‐up) that is frequently mentioned in reviews . The low rate of progression observed in the present study has recently been confirmed in a population‐based cohort study, with 6.4%, 17.3%, and 26.4% of patients switching from nonradiographic to radiographic disease after 5, 10, and 15 years of follow‐up, respectively .…”

Ankylosing Spondylitis and Axial Spondyloarthritis

“…Progression to ankylosing spondylitis occurs in only a minority of patients who have had nonradiographic axial spondyloarthritis for a decade or more. 12 It is unclear whether nonradiographic axial spondyloarthritis and ankylosing spondylitis reflect a single entity that varies along a continuum of duration and severity or whether nonradiographic axial spondyloarthritis includes one or more pathogenetically distinct subsets of disease that either have not been previously recognized or have been given other diagnoses, including undifferentiated spondyloarthritis. [13][14][15] Among patients with nonradiographic axial spondyloarthritis, there is a significantly higher proportion of female patients, a shorter median duration of disease, and lower levels of inflammatory markers than among those with ankylosing spondylitis.…”

Assessing the construct validity of clinical tests to identify sacroiliac joint inflammation in patients with non‐radiographic axial spondyloarthritis

“…It is also important to acknowledge that the current “gold standard” for identifying sacroiliitis, is neither 100% sensitive nor specific for these articular structures. Recently, the use of MRI as criterion for classification of nrAxSpA has been questioned . A population‐based cohort study showed only a minority (26%) of patients presenting with MRI inflammation evolving to AS (the radiographic subset of the disease) with an average follow‐up of 10 years .…”

“…Recently, the use of MRI as criterion for classification of nrAxSpA has been questioned . A population‐based cohort study showed only a minority (26%) of patients presenting with MRI inflammation evolving to AS (the radiographic subset of the disease) with an average follow‐up of 10 years . Furthermore, MRI inflammatory changes are also seen in individuals who have had recent mechanical stress, such as runners as well as women in the post‐partum period .…”

“…The ASAS criteria were designed to facilitate earlier detection of axial SpA with the aim of improving outcomes in SpA patients. Studies suggest that approximately one in four patients with nrAxSPA will progress to true AS; however, in general patients with nrAxSPA do not appear to differ symptomatically from those with AS across a range of outcomes . Moreover, there is increasing evidence that treatment with anti‐tumor necrosis factor (TNF) alpha inhibitors may retard radiologic progression through the abrogation of inflammation .…”