The findings suggest that researchers may soon be possible for clinicians to identify when patients are at highest risk for seizures, allowing patients to plan around these brief but potentially dangerous events.
Study's senior author Vikram Rao, MD, PhD, an assistant professor of neurology at UCSF, said, "One of the most disabling aspects of having epilepsy is the seeming randomness of seizures. If your neurologist can't tell you if your next seizure is a minute from now or a year from now, you live your life in a state of constant uncertainty, like walking on eggshells. The exciting thing here is that we may soon be able to empower patients by letting them know when they are at high risk and when they can worry less."
During a seizure, abnormal electrical activity in the brain can cause numerous symptoms, including a loss of awareness or consciousness, changes in the senses, hallucinations, numbness, feelings of electric shocks, drooling, convulsions and difficulty in breathing.
The new study, based on recordings from the brains of 37 patients fitted with NeuroPace implants, a brain stimulation device that can quickly halt seizures by precisely stimulating a patient's brain as a seizure begins, confirmed previous clinical and research observations of daily cycles in patients' seizure risk, explaining why many patients tend to experience seizures at the same time of day.
But the study also revealed that brain irritability rises and falls in much longer cycles lasting weeks or even months, and that seizures are more likely to occur during the rising phase of these longer cycles, just before the peak.
The lengths of these long cycles differ from person to person but are highly stable over many years in individual patients, the researchers found.
The researchers show in the paper that when the highest-risk parts of a patient's daily and long-term cycles of brain irritability overlap, seizures are nearly seven times more likely to occur than when the two cycles are mismatched.
The team is now using data to develop a new approach to forecasting patients' seizure risk, which could allow patients to avoid potentially dangerous activities such as swimming or driving when their seizure risk is highest, and to potentially take steps (such as additional medication doses) to reduce their seizure risk.
Rao concluded by saying, "I like to compare it to a weather forecast. In the past, the field has focused on predicting the exact moment a seizure will occur, which is like predicting when lightning will strike. That's pretty hard. It may be more useful to be able tell people there is a 5 percent chance of a thunderstorm this week, but a 90 percent chance next week. That kind of information lets you prepare."
The study was published in journal Nature Communications.
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