From the Research
Approximately 70-90% of patients with focal seizures show EEG abnormalities when appropriate recording techniques are used. Standard routine EEG may only detect abnormalities in about 50% of cases during the interictal period (between seizures), but this detection rate increases significantly with repeated recordings, sleep-deprived EEG, and prolonged monitoring 1. The most common EEG finding in focal seizures is focal interictal epileptiform discharges, typically appearing as sharp waves or spikes localized to the region of seizure onset. These abnormalities reflect the hyperexcitable neuronal networks responsible for seizure generation.
The likelihood of detecting abnormalities increases with the use of additional electrodes (such as anterior temporal electrodes), activation procedures (hyperventilation, photic stimulation), sleep recording, and especially with prolonged video-EEG monitoring over 24-72 hours. It's essential to note that a normal EEG does not rule out epilepsy, as the abnormal electrical activity may occur intermittently or in brain regions not easily accessible to scalp electrodes. This is why clinical history remains crucial in diagnosis even when EEG findings are negative.
Some studies have investigated the predictive value of EEG abnormalities in patients with focal seizures. For instance, a study published in 2015 found that focal EEG abnormalities were predictive of later epilepsy in patients with febrile seizures 2. However, the most recent and highest-quality study on this topic is not directly related to the predictive value of EEG abnormalities but rather focuses on the effectiveness and cost-effectiveness of different antiepileptic drugs for newly diagnosed focal epilepsy 3.
In terms of the percentage of EEG abnormalities in focal seizures, the provided evidence does not give a specific percentage but highlights the importance of using appropriate recording techniques to increase the detection rate of abnormalities. The detection rate of EEG abnormalities in focal seizures can be as high as 70-90% with appropriate recording techniques. This information is crucial for clinicians to make informed decisions about diagnosis and treatment.
Key points to consider:
- The detection rate of EEG abnormalities in focal seizures increases with repeated recordings, sleep-deprived EEG, and prolonged monitoring.
- Focal interictal epileptiform discharges are the most common EEG finding in focal seizures.
- Clinical history remains crucial in diagnosis even when EEG findings are negative.
- The use of additional electrodes and activation procedures can increase the likelihood of detecting abnormalities.