Background/Purpose: Juvenile idiopathic arthritis (JIA) is the most common childhood onset inflammatory arthritis.  The last estimates of incidence of this disease in the United Kingdom are from nearly 30 years ago, prior to international classification consensus and the emergence of paediatric and adolescent rheumatology as a specialty.  The aim of this study was to estimate incidence of JIA from primary care records in the UK since 2000.

Methods: The study used data from the Clinical Practice Research Datalink (CPRD) Gold, a database of UK primary care records considered broadly representative of the UK as a whole in terms of age, gender and ethnicity.  A pre-defined list of JIA Read codes were used to identify incident cases annually from 2000-2018.  Incidence rates with 95% confidence intervals (CI) were calculated.  The denominator was the population of CPRD < 16 years old on the 31st December each year.  Age and gender stratified rates were calculated. Direct standardisation was used to estimate the UK IR using the Office for National Statistics mid-2017 population data (latest available). Incidence rates in 5-year groupings were calculated 2000-2015 to identify any change over time.

Results: There were 1927 incident cases of JIA from 2000-2018, from a total population of 23,328,676 children < 16 years old in CPRD.  This gave a total incident rate (IR) (95% confidence interval (CI)) of 8.26 (7.90-8.64) per 100,000 population.  There was a slight female preponderance, with IR (95% CI) 9.83 (9.27-10.43) per 100,000 in females, compared to 6.78 (6.33-7.27) per 100,000 in males.  Age adjusted direct standardisation to the UK population estimated a total IR of 9.66 per 100,000 person years.  Incident rates by age group are shown in table 1.  There appeared to be a slightly lower incidence in middle childhood compared to early childhood and adolescents, as well as infancy where lower rates may be due to difficulties in recognising the disease.   IRs over time did not appear to change (figure 1).

Conclusion: This is the first study to provide contemporary UK estimates of the incidence of JIA for nearly 30 years.  We have shown JIA is more common in girls compared to boys, and is slightly more common in early childhood and adolescence compared to other age groups.  Incidence appears to have been stable over a fifteen-year period.  These data provide important information for patients, their families and healthcare providers; in addition, they are vital for appropriate resource planning and service provision in paediatric and adolescent rheumatology.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/incidence-of-juvenile-idiopathic-arthritis-in-the-united-kingdom-estimates-from-a-national-primary-care-dataset/