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Background: CPRD and linked HES provide a national resource to further explore the epidemiology of Behcet's syndrome (BS) in a western population. Conditions with both phenotypic and genetic overlap could also be examined along with demographic factors during the evolution of the BS phenotype towards a confirmed diagnosis. Objectives: 1. Establish epidemiology of BS: Annual incidence rate and prevalence per million person years will be calculated stratified by age, sex, ethnicity and patient level/area-based deprivation. 2. Explore risk factors for BS including age, smoking, obesity, ethnicity, gender, socio-economic deprivation and presence of phenotypically linked, MHC class 1 opathy related diseases. 3. Examine time to diagnosis of BS from first recorded symptom: oral or genital apthosis, ocular manifestations, cutaneous, neurological, GI, and vascular manifestations. Methods: CPRD and linked HES databases were used to estimate yearly point prevalence and incidence rates for BS using read code diagnosis of BS in either CPRD or CPRD linked HES between2001 to 2020. For those with both HES and CPRD read code of BS, the earliest date was used for diagnosis. A retrospective matched case control study design was used to evaluate BS risk (odds ratio) for a variety of pre-selected covariates of interest. Controls were selected at a 1: 4 ratio (age, gender and practice matched). To evaluate the relationship of phenotypically related inflammatory conditions (MHC Class 1 opathy) at baseline on BS risk in cases versus controls, logistic regression was used to calculate unadjusted odds ratios. We estimated median time from first clinical code of a manifestation of interest and CPRD/HES confirmed diagnosis of BS. CPRD obtains annual research ethics approval from the UK's Health Research Authority Research Ethics Committee (reference no. 05/MRE04/87). The use of CPRD Gold/Aurum data for the study was approved by the CPRD Independent Scientific Advisory Committee (reference no. 22₀01725). Results: A total of 4810 cases of BS were noted during the study period. Prevalence of BS was 19. 07 per 100, 000 (95% CI 19. 93, 18. 23) in 2020, rising compared to previous years (12. 5/100, 000 in 2006) (Figure 1). Incidence of BS was stable, 0. 89 per 100, 000 (95% CI 1. 09, 0. 71). Both prevalence and incidence were highest amongst females, in Southwest England and amongst those of mixed-race ethnicity. Prevalence and incidence were highest amongst the 31 – 40 age group in 2020. A sample of 1752 cases of BS in CPRD were compared with 5716 age and gender matched controls. As expected, there was a significantly increased risk of genital ulceration (OR 88. 21 (41. 70-221. 91), uveitis (OR 28. 57 (19. 12-44. 18) and oral ulceration (OR 27. 50 (21. 62-35. 33) amongst participants with BS compared to controls. Of interest, coded conditions with potential phenotypic and genetic overlap (MHC Class 1 opathy concept) including Inflammatory bowel disease, Ankylosing Spondylitis, Reactive Arthritis, Psoriatic and enteropathic arthritis were significantly associated with BS compared to controls at baseline. Using Read and Snomed codes a chronological sequence for appearance of phenotypic element leading to a BS diagnosis was established. The shortest median time to diagnosis of BS was 85 days (IQR 0, 9412) from having the first clinical code for genital ulceration and for oral ulceration 886 days (IQR 274. 75, 16613) (Figure 2). Conclusion: The prevalence of BS appears higher than previously thought in the UK consistent with our previous observations. Misclassification with phenotypically and genetically related conditions may also be a factor. BS phenotype might have multiple origins through conditions with genetic and phenotypic overlap as risk of BS seems to be increased in those with a genetically linked condition. Evident diagnostic delay can be avoided by increased recognition of key clinical manifestations. Exploring such factors could be further facilitated by establishing a UK BS registry. REFERENCES: NIL. Acknowledgements: Behcets UK, SWBH NHS Trust and Behcets Centre of Excellence, Birmingham. Disclosure of Interests: Priyanka Chandratre Honorarium from Novartis and UCB, Joht Chandan: None declared, Samuel Cusworth: None declared, Ben Hammond: None declared, Rasiah Thayakaran: None declared, Nicola Adderley: None declared, Deva Situnayake: None declared.
Chandratre et al. (Sat,) studied this question.