CORTICO-THALAMIC LOOP OSCILLATIONS MAY NOT BE NECESSARY FOR 3/SECOND CLONIC EPILEPTIC SEIZURES WHEN INDUCED BY SYNCOPES IN THE CONTEXT OF ANOXIC-EPILEPTIC SEIZURES
Abstract number :
2.205
Submission category :
Year :
2003
Submission ID :
1063
Source :
www.aesnet.org
Presentation date :
12/6/2003 12:00:00 AM
Published date :
Dec 1, 2003, 06:00 AM
Authors :
John B.P. Stephenson Fraser of Allander Neurosciences Unit and EEG Department, Royal Hospital for Sick Children, Glasgow, Scotland, United Kingdom
Animal studies suggest that cortico-thalamic oscillations underlie generalised epileptic seizures with rhythmic bilateral EEG discharges. An opportunity to test this hypothesis in man arises in the so-called anoxic-epileptic seizure. In this combinatory event hypoxia from a severe syncope induces first an isoelectric EEG and thereafter an epileptic seizure, usually [quot]generalised[quot] clonic in appearance. If the cortex is involved in the 3/second rhythmic bilateral limb jerking then one would expect that 3/second generalised spike and wave EEG discharges would coincide with the onset of this rhythmic myoclonus. On the other hand, if a brainstem generator more resistant to hypoxia than the cortex is responsible for this rhythmicity, then one might expect to see rhythmic limb jerking while the EEG remains isoelectric.
I reviewed the best available published recording of an anoxic-epileptic seizure. This is shown in figure 11.4 in [italic]Fits and Faints[/italic]1. The trace comes from a boy of about 1 year in whom brief ocular compression was used to reproduce an anoxic-epileptic seizure to confirm the clinical diagnosis.
The resulting cardiac asystole leads to an isoelectric EEG after about 10 seconds. Down-beat nystagmus then gives prominent oculogenic oscillations under frontopolar electrodes without true EEG change. Hypoxic nonepileptic tonic extensions follows. Then, close to the time of return of EKG complexes and not less than 5 seconds before return of EEG activity, 3/second rhythmic bursts of EMG activity with embedded movement artefact are seen both on the EEG and on the EKG channels. By 10 seconds after the onset of this rhythmic clonus generalised spike wave is clearly seen on EEG, later slowing in frequency.
This single observation albeit in a young child suggests that cortico-thalamic oscillation is not necessary for the genesis of rhythmic clonic epileptic activity and is more in keeping with a less oxygen dependent brainstem generator being responsible.
1. Stephenson JBP. [italic]Fits and faints[/italic]. MacKeith Press London 1990: 122-3.