Ictal magnetoencephalographic study in a patient with ring 20 syndrome
- 1Department of Psychiatry and Neurology, Hokkaido University School of Medicine, Sapporo, Japan
- 2Department of Neurosurgery, Chitose City Hospital, Sapporo, Japan
- 3Research Institute for Electronic Science, Hokkaido University, Sapporo, Japan
- Correspondence to: Dr N Tanaka Department of Psychiatry and Neurology, Hokkaido University School of Medicine, North 15, West 7, Sapporo 060-8638, Japan; naoromed.hokudai.ac.jp
- Received 9 June 2003
- Accepted 6 August 2003
- Revised 6 August 2003
Abstract
Objective: To report the ictal magnetoencephalography (MEG) in a patient with ring chromosome 20 mosaicism, a rare chromosomal anomaly associated with intractable epilepsy.
Methods: MEG and simultaneous EEG were recorded with a 204 channel whole head MEG system. Ten habitual seizures occurred during the acquisition, which was done twice. The equivalent current dipoles (ECDs) for ictal discharges on MEG were calculated using a single dipole model. The ECDs were superimposed on a magnetic resonance image.
Results: During the seizures, EEG showed prolonged bursts of 5–6 Hz high voltage slow waves with spike components, dominantly in the bilateral frontal region. MEG showed epileptiform discharges corresponding to the ictal EEG. Ictal discharges on MEG were dominant in the frontal area in the initial portion, and then spread in the bilateral temporal area in the middle of the seizure. ECDs obtained from the spikes of the initial portion were clustered in the medial frontal lobe.
Conclusions: The source of the ictal MEG was localised in the medial frontal lobe. The findings suggest that the mechanism underlying epilepsy in this case might be similar to medial frontal lobe epilepsy. Ictal MEG is a valuable tool for detecting the site of seizure onset.
- ECD, equivalent current dipole
- MEG, magnetoencephalography
- WAIS-R, Wechsler adult intelligence scale, revised
Footnotes
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Competing interests: none declared
