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. 2021 Dec;7(3):e001888.
doi: 10.1136/rmdopen-2021-001888.

Changes in ankylosing spondylitis incidence, prevalence and time to diagnosis over two decades

Samantha S R Crossfield  1   2 , Helena Marzo-Ortega  2   3 , Sarah R Kingsbury  2   3 , Mar Pujades-Rodriguez  4 , Philip G Conaghan  2   3
Affiliations

Changes in ankylosing spondylitis incidence, prevalence and time to diagnosis over two decades

Samantha S R Crossfield et al. RMD Open. 2021 Dec.

Abstract

Objectives: To assess changes in ankylosing spondylitis (AS) incidence, prevalence and time to diagnosis, between 1998 and 2017.

Methods: Using UK GP data from the Clinical Practice Research Datalink, we identified patients diagnosed with AS between 1998 and 2017. We estimated the annual AS incidence, prevalence and length of time from first recorded symptom of back pain to rheumatology referral and diagnosis.

Results: We identified 12 333 patients with AS. The incidence declined from 0.72 (±0.14) per 10 000 patient-years in 1998 to 0.39 (±0.06) in 2007, with this decline significant only in men, then incidence rose to 0.57 (±0.11) in 2017. By contrast, prevalence increased between 1998 and 2017 (from 0.13%±0.006 to 0.18%±0.006), rising steeply among women (from 0.06%±0.05 to 0.10%±0.06) and patients aged ≥60 (from 0.14%±0.01 to 0.26%±0.01). The overall median time from first symptom to rheumatology referral was 4.87 years (IQR=1.42-10.23). The median time from first symptom to diagnosis rose between 1998 and 2017 (from 3.62 years (IQR=1.14-7.07) to 8.31 (IQR=3.77-15.89)) and was longer in women (6.71 (IQR=2.30-12.36)) than men (5.65 (IQR=1.66-11.20)).

Conclusion: AS incidence declined significantly between 1998 and 2007, with an increase between 2007 and 2017 that may be explained by an improvement in the recognition of AS or confidence in diagnosing AS over time, stemming from increased awareness of inflammatory back pain and the importance of early treatment. The rising AS prevalence may indicate improved patient survival. The persisting delay in rheumatology referral and diagnosis remains of concern, particularly in women.

Keywords: ankylosing; ankylosing spondylitis; arthritis; epidemiology; spondylitis.

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Conflict of interest statement

Competing interests: SSRC reports a studentship grant from the Medical Research Council Leeds Medical Bioinformatics Centre. HM-O reports grant support from Janssen and Novartis, and personal fees from AbbVie, Celgenes, Eli-Lilly, Janssen, Novartis, Pfizer, Takeda and UCB. PGC reports personal fees from AbbVie, BMS, Eli Lilly, Galapagos, Gilead, Novartis and Pfizer. MP-R is currently employed by IQVIA, a research contract organisation.

Figures

Figure 1
Figure 1
Study design for the ‘at risk’ cohort. AS diagnoses recorded during the period represented by a dashed line (observed/enrolment in database) contributed to prevalence but not incidence estimates. AS, ankylosing spondylitis.
Figure 2
Figure 2
Study flow diagram of cohort selection. AS, ankylosing spondylitis; CPRD, Clinical Practice Research Datalink; UTS, up to standard.
Figure 3
Figure 3
Annual incidence rate among women and men. Annual incidence rate among women and men, 1998–2017; (A) all patients (N=8 052 546); (B) patients in the sensitivity analysis (N=7 919 770).
Figure 4
Figure 4
Annual percentage prevalence, by sex and by age-group. Annual percentage prevalence of ankylosing spondylitis (AS) (A) among women and men for all patients, 1998–2017 (N=8 052 980) and for patients in the sensitivity analysis, 1998–2016 (N=7 413 674); (B) per age-group among patients aged 18–99, 1997–2017 (N=7 532 700). Sensitivity analysis=patients with an additional diagnostic or AS measurement code recorded >7 days later.
Figure 5
Figure 5
Annual median time in years from first recorded symptom to diagnosis. Annual median time in years from first recorded symptom to diagnosis, with IQR, 1998–2017 (N=2120). Dashed line represents the overall annual diagnostic delay, and the shaded area the IQR.
See this image and copyright information in PMC

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