Counterintuitive finding
The relationship between late-onset epilepsy and subsequent dementia was stronger in patients without stroke. The investigators offered a possible explanation for this counterintuitive finding. “We observed an interaction between [late-onset epilepsy] and stroke, with a lower (but still substantial) association between [late-onset epilepsy] and dementia in those with a history of stroke. This may be due to the known strong association between stroke and dementia, which may wash out the contributions of [late-onset epilepsy] to cognitive impairment,” the researchers wrote.
“There may also be under-capturing of dementia diagnoses among participants with stroke in the ascertainment from [Centers for Medicare & Medicaid Services] codes, as physicians may be reluctant to make a separate code for ‘dementia’ in those with cognitive impairment after stroke,” they added.
When the researchers restricted the analysis only to participants who attended visits 5 and 6 and had late-onset epilepsy ascertainment available, they found that the relative risk ratio for dementia at visit 6 was 2.90 (95% CI, 1.22-6.92; P = .009). The RRR for MCI was 0.97 (95% CI, 0.39-2.38; P = .803). The greater functional impairment in patients with late-onset epilepsy may explain the lack of a relationship between late-onset epilepsy and MCI.
“It will be important for neurologists to be aware of the possibility of cognitive impairment following late-onset epilepsy and to check in with patients and family members to see if there are concerns,” said Dr. Johnson.
“We should also be talking about the importance of lowering other risk factors for dementia by making sure cardiovascular risk factors are controlled and encouraging physical and cognitive activity,” she added.
The results require confirmation in a clinical population, the investigators noted. In addition, future research is necessary to clarify whether seizures directly increase the risk of dementia or whether shared neuropathology between epilepsy and dementia explains the risk.
“In the near future, I plan to enroll participants with late-onset epilepsy in an observational study to better understand factors that may contribute to cognitive change. Collaborations will be key as we seek to further understand what causes these changes and what could be done to prevent them,” Dr. Johnson added.
Strengths and weaknesses
In an accompanying editorial, W. Allen Hauser, MD, professor emeritus of neurology and epidemiology at Columbia University in New York, and colleagues noted that the findings support a bidirectional relationship between dementia and epilepsy, adding that accumulation of amyloid beta peptide is a plausible underlying pathophysiology that may explain this relationship.
Future research should clarify the effect of factors such as seizure type, seizure frequency, and age of onset on the risk of dementia among patients with epilepsy, the editorialists wrote. Such investigations could help elucidate the underlying mechanisms of these conditions and help to improve treatment, they added.
Commenting on the findings, Ilo Leppik, MD, professor of neurology and pharmacy at the University of Minnesota in Minneapolis described the research as “a very well-done study by qualified researchers in the field. … For the last century, medicine has unfortunately become compartmentalized by specialty and then subspecialty. The brain and disorders of the brain do not recognize these silos. … It is not a stretch of the known science to begin to understand that epilepsy and dementia have common anatomical and physiological underpinnings.”
The long period of prospectively gathering data and the measurement of cognitive function through various modalities are among the study’s great strengths, said Dr. Leppik. However, the study’s weakness is its reliance on Medicare claims data, which mainly would reflect convulsive seizures.
“What is missing is how many persons had subtle focal-unaware seizures that may not be identified unless a careful history is taken,” said Dr. Leppik. “Thus, this study likely underestimates the frequency of epilepsy.”
Neurologists who evaluate a person with early dementia should be on the lookout for a history of subtle seizures, said Dr. Leppik. Animal studies suggest treatment with levetiracetam or brivaracetam may slow the course of dementia, and a clinical study in participants with early dementia is underway.
“Treatment with an antiseizure drug may prove to be beneficial, especially if evidence for the presence of subtle epilepsy can be found,” Dr. Leppik added.
Greater collaboration between epileptologists and dementia specialists and larger studies of antiseizure drugs are necessary, he noted. “These studies can incorporate sophisticated structural and biochemical [analyses] to better identify the relationships between brain mechanisms that likely underlie both seizures and dementia. The ultimate promise is that early treatment of seizures may alter the course of dementia,” Dr. Leppik said.
The study by Dr. Johnson and colleagues was supported by a contract from the National Institute on Aging; ARIC from the National Heart, Lung, and Blood Institute; the National Institutes of Health; and the Department of Health & Human Services. The authors and Dr. Leppik have disclosed no relevant financial relationships.
A version of this article originally appeared on Medscape.com.