Prevalence of epilepsy: a population-based cohort study in Denmark with comparison to Global Burden of Disease (GBD) prevalence estimates.

Background: The Global Burden of Disease Study (GBD) produces prevalence estimates for 'idiopathic epilepsy' (ie, of unknown aetiology) and 'secondary epilepsy' (ie, with known aetiology) but does not report prevalence by underlying aetiologies for 'secondary epilepsy'.

Methods: We used nationwide, population-based register data from Denmark to identify underlying causes of epilepsy and their contribution to prevalence of 'secondary epilepsy' and compared with global prevalence data from GBD 2019. We identified all persons with a hospital-based epilepsy diagnosis and a filled prescription for antiseizure medication between 1 January 2009 and 31 December 2018. Epilepsy was categorised into 'idiopathic' or 'secondary' and 'total epilepsy' as the sum of the two epilepsy categories.

Results: On 31 December 2018, a total of 5 784 284 individuals (49.7% males) were living in Denmark including 40 336 with epilepsy (51.5% males). Perinatal conditions, traumatic brain injury, brain tumours and stroke were prominent underlying causes of 'secondary epilepsy'. The prevalence of 'total epilepsy' in Denmark was 697 (95% CI 691 to 704) per 100 000 population (264 (95% CI 260 to 269) for 'secondary epilepsy' and 433 (95% CI 428 to 438) for 'idiopathic epilepsy'). In the GBD 2019 Study, the prevalence of 'total epilepsy' in 2018 was 682 (95% uncertainty interval (UI) 586 to 784) per 100 000 population (359 (95% UI 324-397) for 'secondary epilepsy' and 324 (95% UI 249 to 404) for 'idiopathic epilepsy').

Conclusions: Prevalence estimates of 'total epilepsy', 'idiopathic epilepsy' and 'secondary epilepsy' in Denmark align with the GBD 2019 estimates. In future studies, it is suggested to explicitly include all types of epilepsy, including 'secondary epilepsy', which is currently estimated as sequelae (consequences) of underlying diseases.