Results of a retrospective analysis show that patients who develop epilepsy at age 67 or older have a threefold increased risk of subsequent dementia versus their counterparts without epilepsy.
Dr. Emily L. Johnson
“This is an exciting area, as we are finding that just as the risk of seizures is increased in neurodegenerative diseases, the risk of dementia is increased after late-onset epilepsy and seizures,” study investigator Emily L. Johnson, MD, assistant professor of neurology at Johns Hopkins University, Baltimore, said in an interview. “Several other cohort studies are finding similar results, including the Veterans’ Health Study and the Framingham Study,” she added.
The study was published online Oct. 23 in Neurology
Bidirectional relationship?
Previous research has established that dementia is a risk factor for epilepsy, but recent studies also suggest an increased risk of incident dementia among patients with adult-onset epilepsy. Several risk factors for late-onset epilepsy, including diabetes and hypertension, also are risk factors for dementia. However, the effect of late-onset epilepsy on dementia risk in patients with these comorbidities has not been clarified.
To investigate, the researchers examined data from the Atherosclerosis Risk in Communities (ARIC) study. Participants include Black and White men and women from four U.S. communities. Baseline visits in this longitudinal cohort study began between 1987 and 1989, and follow-up included seven additional visits and regular phone calls.
The investigators identified participants with late-onset epilepsy by searching for Medicare claims related to seizures or epilepsy filed between 1991 and 2015. Those with two or more such claims and age of onset of 67 years or greater were considered to have late-onset epilepsy. Participants with preexisting conditions such as brain tumors or multiple sclerosis were excluded.
ARIC participants who presented in person for visits 2, 4, 5, and 6 underwent cognitive testing with the Delayed Word Recall Test, the Digit Symbol Substitution Test, and the Word Fluency Test.
Testing at visits 5 and 6 also included other tests, such as the Mini-Mental State Examination, the Boston Naming test, and the Wechsler Memory Scale-III. Dr. Johnson and colleagues excluded data for visit 7 from the analysis because dementia adjudication was not yet complete.
The researchers identified participants with dementia using data from visits 5 and 6 and ascertained time of dementia onset through participant and informant interviews, phone calls, and hospital discharge data. Participants also were screened for mild cognitive impairment (MCI) at visits 5 and 6.
Data were analyzed using a Cox proportional hazards model and multinomial logistic regression. In subsequent analyses, researchers adjusted the data for age, sex, race, smoking status, alcohol use, hypertension, diabetes, body mass index (BMI), APOE4 status, and prevalent stroke.
The researchers found that of 9,033 study participants, 671 had late-onset epilepsy. The late-onset epilepsy group was older at baseline (56.5 vs. 55.1 years) and more likely to have hypertension (38.9% vs. 33.3%), diabetes (16.1% vs. 9.6%), and two alleles of APOE4 genotype (3.9% vs. 2.5%), compared with those without the disorder.
In all, 1,687 participants developed dementia during follow-up. The rate of incident dementia was 41.6% in participants with late-onset epilepsy and 16.8% in participants without late-onset epilepsy. The adjusted hazard ratio of subsequent dementia in participants with late-onset epilepsy versus those without the disorder was 3.05 (95% confidence interval, 2.65-3.51).
The median time to dementia ascertainment after late-onset epilepsy was 3.66 years.