Background Non-radiographic axial spondyloarthritis (nr-axSpA) and radiographic axial SpA (=ankylosing spondylitis – AS) are considered currently as two stages of axial SpA. We reported recently that about 12% of the patients with non-radiographic axial SpA progress in AS over 2 years . Although it can be expected that in the first years after back pain onset non-radiographic (without definite sacroiliitis on the x-ray) SpA is more likely to see than established AS, their frequencies and their ratio in relation to back pain duration at the referral time point is not known.
Objectives To estimate the ratio of nr-axSpA and AS diagnoses in relation to the symptom duration in patients referred to a rheumatologist because of chronic back pain and suspicion of axial SpA.
Methods In this monocenter study performed in Berlin  orthopaedists and primary care physicians were requested to refer patients with chronic low back pain (duration >3 months) and onset of back pain before <45 years of age to a SpA-specialized rheumatology outpatient clinic for further diagnostic investigation if at least one of the following screening parameters was present: 1) inflammatory back pain, 2) positive HLA-B27, and 3) sacroiliitis detected by imaging. The final diagnosis was made according to the opinion of rheumatologist.
Results In total, 522 patients were referred. A diagnosis of definite axial SpA was made in 43.7% of the cases. Among patients who were referred with chronic back pain axial SpA was diagnosed in a similar percentage of about 50% if symptom (back pain) duration was <9 years and of 36% if symptom duration was >9 years. The ratios of nr-axSpA to AS among patients with definite axial SpA in relation to the duration of back pain at the time-point of referral are presented in figure. Nr-axSpA represented the majority of patient (67.3%) only if duration of back pain was 1 year and less at the time of referral. Between 1 and 6 years of back pain duration the probability of nr-axSpA and AS was nearly equal. In patients with back pain duration of more than 6 years, AS was more likely to be diagnosed than nr-axSpA, and this increased further over time.
Conclusions Non-radiographic axial SpA is a relevant diagnosis in patients with axial SpA at any time point, however, the probability of non-radiographic form of axial SpA is highest if symptom duration is short.
Poddubnyy D, et al. Ann Rheum Dis 2011;70:1369-74.
Brandt HC, et al. Ann Rheum Dis 2007;66:1479-84.
Disclosure of Interest None Declared