Epilepsy was strongly associated with dementia before age 65

Design

Nationwide nested case-control studies (France, Sweden) and a French retrospective cohort

Population

11,360 French and 16,433 Swedish young-onset dementia cases with matched controls; 206,000 French adults aged 30 to 55 in the cohort

Primary outcome

Young-onset dementia (diagnosed before age 65)

Effect

French OR 3.76 (95% CI 3.42 to 4.14) for prior epilepsy codes; 10-year cumulative incidence 2.20% vs 0.21% (adjusted HR 6.02, 95% CI 4.98 to 7.26)

This study ran three nationwide analyses. A French nested case-control study compared 11,360 people with young-onset dementia diagnosed between 40 and 64 years with 113,600 matched controls. A Swedish replication used 16,433 cases and 164,330 controls. A French cohort followed adults aged 30 to 55 with new epilepsy, existing epilepsy or no epilepsy for up to 10 years.

In France, 12.5% of cases and 1.2% of controls had earlier epilepsy-related diagnoses (adjusted OR 3.76, 95% CI 3.42 to 4.14), and 27.3% vs 10.3% had antiseizure medication dispensed (adjusted OR 1.44, 95% CI 1.36 to 1.52). In the cohort, 10-year cumulative incidence of young-onset dementia was 2.20% with new epilepsy and 0.21% without (adjusted HR 6.02, 95% CI 4.98 to 7.26); with long-standing epilepsy the hazard ratio was 5.38. Associations weakened with longer lags but persisted beyond five years.

These are registry associations. Early dementia can itself cause seizures, and the lag analyses address this only partly. In practice, cognitive symptoms in a person with epilepsy who is under 65 deserve a proper assessment and not an automatic attribution to medication or seizures.

• Previous epilepsy codes were present in 12.5% of French young-onset dementia cases vs 1.2% of controls (adjusted OR 3.76).
• The 10-year risk of young-onset dementia was 2.20% after new epilepsy at 30 to 55 years vs 0.21% without epilepsy.
• The association persisted beyond a five-year lag, which argues against pure reverse causation.
• Consider a formal cognitive assessment when a person with epilepsy has new memory or behaviour change before 65.
• The data show association only, and the absolute 10-year risk after epilepsy remains about 2%.

Why it matters

Epilepsy is usually discussed as a late-life dementia risk, and this extends the link to midlife.

Don't overread it

These are registry associations, and neither design can show that epilepsy or its drugs cause dementia.

The statistics, in plain English

The adjusted hazard ratio of 6.02 means that, over the 10 years, people with new epilepsy developed young-onset dementia at about six times the rate of those without. The absolute difference is much smaller: about 2.2 vs 0.2 per 100 people. A very high relative risk of a rare outcome still leaves most people with epilepsy free of early dementia.

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