Epilepsy Incidence in Older Adults Is Highest Among Black Patients

VANCOUVER—At a rate of 2.5 per 1,000 person-years, epilepsy incidence in adults age 65 and older is common, according to a retrospective analysis of clinical and administrative data. "To put these study results in context, this incidence rate is 1.5 times higher than that of Parkinson's disease," said Hyunmi Choi, MD, MS, of Columbia University, New York City. Most important, she said, is the finding that black older adults have double the incidence rate of their white counterparts, independent of stroke. "These findings underscore the need for further studies that directly examine the mechanisms by which race affects epilepsy risk," said Dr. Choi at the 68th Annual Meeting of the American Academy of Neurology.

Hyunmi Choi, MD, MS

Geographic and Cultural Diversity

Dr. Choi and colleagues from Columbia University and the University of Washington in Seattle, examined data from the Cardiovascular Health Study (CHS), a prospective cohort study of coronary heart disease and stroke. CHS began in 1989 and enrolled 5,201 adults age 65 and older from multiple regions of the country: Sacramento county, California; Washington county, Maryland; Forsyth county, North Carolina; and Pittsburgh, Pennsylvania. A second cohort of 687 predominantly African American participants was enrolled in 1992. In-person evaluations were conducted at baseline, followed by annual in-person evaluations interspersed with phone calls every six months. "Recently, CHS merged its data with those of the Centers for Medicare and Medicaid Services (CMS)," Dr. Choi said.

The researchers used multiple data sources to identify potential epilepsy cases, including self report, information on antiepileptic medication, hospitalization discharge claims data, and outpatient CMS claims data using International Classification of Diseases, ninth edition codes. "Two independent reviewers applied the specific criteria to classify the cases, then we assessed the agreement between them. All discordant cases were discussed, and we arrived at a final consensus diagnosis." The study end points were prevalent epilepsy (ie, those who had epilepsy at baseline) and incident epilepsy (ie, those who developed epilepsy during follow-up).

Incidence and Prevalence Data

Dr. Choi and colleagues found the inter-rater reliability to be high and, in the final analysis, identified 335 participants from the CHS cohort with probable epilepsy at baseline. "This is the group that we used to define an overall epilepsy prevalence of 5.7% out of 5,888 participants," Dr. Choi said. Black participants with a prior history of transient ischemic attack were more likely to have prevalent epilepsy.

In addition, Dr. Choi and colleagues identified 120 participants who developed epilepsy during follow-up, for an overall incidence rate of 2.5 per 1,000 person-years, which is similar to that of prior research by Faught and colleagues, she pointed out. In the current study, the incidence rate was elevated in black participants at 4.2 per 1,000 person-years versus 2.1 per 1,000 person-years for white participants.

In addition, Dr. Choi and colleagues identified 120 participants who developed epilepsy during follow-up for an overall incidence rate of 2.5 per 1,000 person-years, which is similar to that of prior research by Faught and colleagues, she pointed out. In the current study, the incidence rate was elevated in black participants at 4.2 for per 1,000 person-years versus 2.1 per 1,000 person-years for white participants.

Adjustment for Stroke Risk

Epilepsy incidence was highest among participants age 75 to 79; however, the incidence rate dropped among those who were older. Using a model that examined participants with a history of cardiovascular risk factors at CHS baseline, Choi and colleagues found that black race, age 75 to 79, and history of stroke were independent risk factors for incident epilepsy. In a second model, which looked at patients who did not have cardiovascular risk factors prior to CHS enrollment but developed these conditions before the onset of epilepsy, black race and incident stroke were independent risk factors for incident epilepsy.

Dr. Choi acknowledged that survival bias may have occurred, whereby healthy participants were retained in the analysis and the sicker patients, possibly with seizures, died earlier. Also, while the analysis adjusted for stroke risk and stroke incidence (which is disproportionately higher in black older adults), other covariates may be more likely to occur in elderly black patients that may have confounded the relationship and increased epilepsy risk.

—Adriene Marshall