Implantable Devices to Detect Impending Seizures
For years, conventional wisdom is that epileptic seizures begin abruptly, just before the manifestation of clinical attacks. However, there is growing evidence that seizures begin minutes or hours before clinical onset. Understanding these processes is helping to bring closer to reality the use of implantable devices which can detect impending seizures and deliver preventative therapy.
In their analysis of quantitative studies of long digital intracranial electroencephalographic (EEG) recordings of patients being evaluated for epilepsy surgery, Dr. Brian Litt (Departments of Neurology and Biomedical Engineering, University of Pennsylvania, Philadelphia, Pennsylvania) and Dr. Javier Echauz (Senior Research Scientist at NeuroPace Inc., Sunnyvale, California) suggest that implantable devices could be used to deliver electrical stimulation treatment or localized (focal) drug infusions on demand. This might eliminate the side effects of long-term anti-seizure medication therapy for some people living with epilepsy.
Interest in such technology has been growing during the past decade. Implantable medical devices, including pacemakers, implantable cardiac defibrillators, and brain stimulators for Parkinson's disease, tremor, pain and seizure control, show tremendous efficacy and have seen both commercial success and public acceptance. Digital EEG technology is widely accepted and methods to record localized seizures from intracranial electrodes have matured. A pre-ictal state before temporal-lobe seizures has been discovered.
The researchers' work gives "convincing evidence" that measurable changes in the EEG take place far in advance of clinical seizures. However, "no truly prospective studies of long-term data have been done". Evidence suggests that seizure precursors may come and go, perhaps over days, as non-clinical seizure activity waxes and wanes in the temporal lobe, before some synchronizing event triggers electrical and clinical seizure onset.
Much remains to be done before these findings, which vary in methods and from person to person, can be developed into reliable, real time seizure-prediction systems. Although such technology has become available only recently, the pace of development is accelerating. A key to this development is access to large quantities of continuous, high-quality human intracranial EEG data, covering all physiological states relevant to seizures, for analysis.
In the view of the researchers, all the approaches used to predict or anticipate seizures provide important insight into seizure generation and probably constitute different ways of viewing the same thing. It is probable that some rarified combination of quantitative features, encompassing parts of many of methods used by major research groups and tailored to individuals, will be required to reliably predict seizures. Real progress will require ongoing collaboration — already begun — between the major research groups involved in this effort.
Sources
Lancet Neurology 2002;1:22-30. "Prediction of epileptic seizures"
http://neurology.thelancet.com/journal/vol1/iiss1/full/lneu.1.1.review_and_opinion.20637.1
