Introduction
The electroencephalogram known as the EEG is one of the main clinical tools used by neurologists to capture a seizure so as to make a diagnosis of epilepsy (Assessment 7). The EEG is a 20 minute procedure in which electrodes are placed on the scalp and brain wave activity is recorded and analyzed. It has many flaws.
EEG limitations
The EEG has serious limitations, chief of which is its short duration. Therefore, the EEG is unable to detect most seizures since most seizures, occur randomly. In lieu of an EEG seizure, physicians rely on the patient and/or family observations of seizure activity for a diagnosis. Thus, physicians make a selection of anti-seizure medication without hard evidence of seizure type and brain location. Although this empirical approach may eventually lead to seizure suppression for the patient, albeit with side effects, it does not advance the field of epilepsy. Treating the symptoms of epilepsy does not add to understanding the disease in order to find a cure.
Insights from intracranial EEG recordings
Cyclic Nature
Brain wave recordings gathered over a period of years in patients with epilepsy have revealed new and important insights into the nature of epilepsy. Basically, these findings show that epilepsy creates a brain where abnormal brain waves (interictal epileptiform activity) occur in cycles of 7, 15, 20-30 days or more.
What this means is that abnormal brain wave activity flows over the brain like ocean waves, rising to a peak and then falling to a baseline. Cycle length is unique to each patient with epilepsy. Importantly, these cycles are predictive of a seizure. This is because it is the rising number of abnormal brain waves of a cycle (the upswing of the cycle) that is associated with seizure onset. Therefore, as the number of abnormal brain waves in each cycle increases to its peak so does the risk of seizures. The waning number of abnormal brain waves of each cycle is not related to seizure risk. The section below describes the supportive experiments.
These are incredibly significant revelations. Firstly, cyclic brain wave activity exists in epilepsy. Secondly, the upward swing to the peak of each cycle is the time of greatest risk for seizures. Therefore, cycle intervals are unique for each patient with epilepsy. Each cycle predicts the next round of seizures (since it follows the rise in wave number per cycle). The knowledge of this relation between cycle and seizure could allow for adequate intervention and prevention.
Source of Insights
These findings appear in a publication by Baud MO et al. Under-sampling in epilepsy: Limitations of conventional EEG. Clinical Neurophysiology Practice 6 : 41–49, 2021. Since copyright laws prevent reproduction of Baud’s figures, it is recommended that the reader obtain the free publication through PubMed (https://pubmed.ncbi.nlm.nih.gov/). The representative EEGs with superimposed seizure events provide visual confirmation of these findings.
These findings are important. Two hundred patients with generalized epilepsy of unknown cause (idiopathic) resistant to antiseizure medication participated in Baud’s clinical study. To suppress their uncontrolled seizures they chose an FDA approved intracranial neurostimulator (RNS_System.NeuroPace, Inc). The device captures the abnormal brain waves (interictal epileptiform activity) described and can respond with a counter stimulation to neutralize the seizure.
Sixty percent of the patients in Baud (2021)’s study exhibit cyclic rhythms as described above. This is certainly a significant number of patients to propose cyclic brain waves rhythms as a basic characteristic of idiopathic generalized epilepsy. However, in the future, it is important to evaluate patients with different types of epilepsy to determine if these cycles also occur across all epilepsies.
Future Challenges
The hurdle to more wide spread research is how to obtain years long data without implantation of electrodes directly into the brain. Intracranial electrode implantation is major invasive surgery and hence, a choice of last resort. Since these observations would never have been obtained in a 20 minute diagnostic EEG, there is clearly a need to develop external devices with the same sensitivity and accuracy as intracranial devices that would be suitable for long term use.
Summary
The exciting findings of Baud et al (2021) uncovered significant novel characteristics in the brains of patients with epilepsy. Results of years long brain recordings of patients with idiopathic generalized epilepsy show abnormal brain wave activity that continuously cycles over intervals of weeks or months. As the number of abnormal waves increase so does the risk of seizures. This is an incredible insight and if confirmed in other types of epilepsy, provides the first step toward understanding the disease of epilepsy.
Great content! Keep up the good work!