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We would like to thank Chattopadhyay et al for their interest in our article presenting the low incident rate of vertebral fractures in an early axial spondyloarthritis (axSpA) population. We have read with interest their comments regarding the external validity of the data we are presenting.1 2
We would like to highlight that the manuscripts the authors are referring to in their letter were focusing only in patients with either very long-standing disease (22.5 years in the Montala study3) or with radiographic involvement (ie, radiographic axSpA, also referred as ankylosing spondylitis) in both studies.4
We would like to emphasise that Devenir des Spondylarthropathies Indifférenciées Récentes (DESIR) is an early axSpA cohorts and to be included, patients could not have axial symptoms for more than 3 years. Furthermore, the presence of radiographic abnormalities was not an inclusion criteria.5 Other early onset axSpA cohorts, such as SPondyloArthritis Caught Early (SPACE) or German Spondyloarthritis Inception cohort (GESPIC) have shown comparable populations. Male gender was 46.6% in the DESIR cohort, 44.6% in the SPACE cohort6 and 51% patients in the GESPIC cohort,7 human leukocyte antigen-B27 was positive in 57.8 %, 67.7% and 79.0% in DESIR, SPACE and GESPIC cohorts, respectively. This phenomenon (early disease presentation being slightly different from long-standing disease) is not unique in axSpA and has also been reported in other diseases such as rheumatoid arthritis (RA). The percentage of anti-citrullinated protein antibody (ACPA)-positive patients included in randomised phase III clinical trials with established disease is usually >75%, whereas the percentage is around 30% in the early RA cohorts.8
Concerning the comment on the diagnostic utility of the low back pain as a criteria for axSpA, we would like also to emphasise that in order to be included in DESIR, patients had to present with inflammatory back pain (and not just low back pain) according to the Calin9 or the Berlin10 criteria for inflammatory back pain for more than 3 months and less than 3 years. But they also have an axSpA diagnosis confidence >5/10 according to the rheumatologist.5 Furthermore, at inclusion, 92.1% patients fulfilled at least one classification for axSpA.
Finally, the authors suggest that perhaps our results are different from the literature due to the inclusion of both nonradiographic and radiographic forms of axSpA. This seems difficult to confirm, since in our analysis, the prevalence of vertebral fracture was not different in both groups, but the incidence was so low overall that it could not be tested.
Handling editor Josef S Smolen
Contributors All the authors contributed equally to the this response.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Patient consent Not required.
Provenance and peer review Commissioned; internally peer reviewed.
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