Studies have established ties between epilepsy and Alzheimer’s disease (AD), but how the two relate in time and what exactly is the nature of seizures in AD patients remain poorly understood. A report published online July 8 in JAMA Neurology addresses these questions by examining patients with epileptic brain activity and either amnestic mild cognitive impairment (aMCI) or AD. Researchers led by Lennart Mucke and Keith Vossel of the Gladstone Institute of Neurological Disease, San Francisco, California, found that in these patients, as was previously found in mouse models, epileptic activity often manifests as non-convulsive seizures. They also report that these types of seizure are associated with earlier cognitive decline. Though preliminary, the results could steer clinicians toward using certain anticonvulsant medications for the treatment of AD in the future.
“Seizures represent an aspect of Alzheimer’s disease that may be treatable,” Vossel told Alzforum. “If nothing else, it could improve symptoms, but in the best-case scenario, we might actually target some mechanisms at play early in the disease process by suppressing aberrant network activity.”
Many studies have characterized epileptic seizures as an endpoint in the late stages of Alzheimer’s (see review by Mendez et al., 2003 and Romanelli et al., 1990). These studies typically described convulsive seizures in people already diagnosed with AD. First author Keith Vossel and colleagues wanted to know if epileptic activity occurred earlier in the disease, how it manifested, what regions of the brain were most affected, and whether it might be helpful in diagnosing AD.
The researchers collaborated with Bruce Miller of the Memory and Aging Center at the University of California, San Francisco, to undertake a retrospective study in which they searched the center’s database for patients diagnosed with amnestic mild cognitive impairment (aMCI) or AD between 2007 and 2012. The scientists narrowed their selection to those with a diagnosis of epilepsy or evidence of epileptic brain activity. They excluded anyone whose seizures had started at a young age or who had other epilepsy risk factors such as stroke or a tumor. Out of 233 people with aMCI, 12 had developed epilepsy after the age of 30. Of the 1,024 diagnosed with AD, 35 had epilepsy and seven more showed signs of epileptiform activity on electroencephalographs (EEG). Mucke emphasized that these numbers likely underestimate the real incidence of epileptiform activity in aMCI and AD, because most patients included in this study did not undergo extensive testing by the most sensitive methods available.
On average, cognition in people with epilepsy declined about five to seven years earlier than in people with normal brain activity. Decline began before age 65 in half of those with epilepsy, but in only about a quarter of those without. Seizures often began around the same time cognition began to deteriorate, when neuropsychological deficits were still mild. Records showed about half of the epilepsy patients had only non-convulsive seizures, exhibiting sensory distortions, speech problems, emotional abnormalities, or feelings of déjà vu. Electroencephalography (EEG) had picked up epileptiform activity in 62 percent of patients with seizures and 6 percent of people who underwent EEG for other reasons.
Epileptic foci were located most commonly in the temporal cortex, followed by the frontotemporal, frontal, and central cortices. In general, long-term video or serial EEGs detected epileptiform activity better than did routine EEG.
That epileptic activity commonly affected the temporal lobes makes it likely that it contributes to memory impairment in these patients, the authors claim. However, its contribution to the overall cognitive decline in AD remains to be determined. “We do not know the extent to which seizures are causing cognitive loss in this particular population,” said Michela Gallagher, John’s Hopkins University, Baltimore, Maryland, who was not involved in the study. Gallagher previously found that reducing hippocampal hyperactivity with a low dose of the anticonvulsant drug levetiracetam improved hippocampal function and memory in people with MCI (see ARF related news), suggesting that such medications could improve cognition.
Studies in transgenic mouse models of AD support that idea. Mucke previously reported that dampening neuronal hyperactivity improves cognition in J20 mice (see ARF related news). That suggests aberrant network excitability could lead to cognitive dysfunction, Mucke told Alzforum. What leads to this hyperactivity? Previous work indicates that in mouse models elevated soluble Aβ appears to be a factor (see ARF related news).
If anti-epileptic treatments might improve cognition, then which drug might work best? Vossel and colleagues found that in the UCSF patient population, some anticonvulsants performed better than others Lamotrigine and levetiracetam, when used at low doses, either partially or fully relieved seizures in about 94 percent of the epilepsy patients. Phenytoin and valproate, which failed in a phase 3 AD trial (see ARF related news) proved less tolerable, and provided less relief. “Together with our previous data from AD animal models, these observations suggest that long-term phenytoin treatment is probably best avoided in this patient population,” Mucke told Alzforum (see Verret et al. 2012 and Sanchez et al. 2012).
The authors acknowledged that this was a small study, relying on data from a single memory center that specializes in early onset dementia, and on notes that lacked standardized methods. Vossel is leading an ongoing prospective study enrolling healthy controls, people with MCI, and AD patients. Using 36-hour video-EEG monitoring and magnetoencephalography (MEG), the scientists hope to identify a subpopulation who might benefit from epilepsy-related diagnostics and medication. So far, in cohorts enriched with early onset AD cases, epileptiform abnormalities are seen in nearly half of those tested. In the future, the scientists plan to spin off a pilot study in which some people with epileptic activity receive levetiracetam.
“This is a much-needed exploration into the association of degenerative disease with seizures,” wrote Gregory Jicha, University of Kentucky Medical Center, Lexington, to Alzforum in an email. However, he cautioned against drawing conclusions about antiepileptic treatments based on this small retrospective study. He also pointed out that no data have yet shown that improved seizure control helps cognitive or behavioral symptoms in dementia.—Gwyneth Dickey Zakaib