Reduced excitability of the motor cortex in untreated patients with de novo idiopathic "grand mal" seizures.
OBJECTIVE
Transcranial magnetic stimulation (TMS) was used to investigate motor cortex excitability, intracortical excitatory, and inhibitory pathways in 18 patients having experienced a first "grand mal" seizure within 48 hours of the electrophysiological test. All had normal brain MRI, and were free of any treatment, drug, or alcohol misuse. Results were compared with those of 35 age matched normal volunteers.


METHODS
The following parameters of responses to TMS were measured: motor thresholds at rest and with voluntary contraction, amplitudes of responses, cortical silent periods, and responses to paired pulse stimulation with interstimulus intervals of 1 to 20 ms.


RESULTS
In patients, there were significantly increased motor thresholds with normal amplitudes of motor evoked potentials (MEPs), suggesting decreased cortical excitability. Cortical silent periods were not significantly different from those of normal subjects. Paired TMS with short interstimulus intervals (1-5 ms) induced normal inhibition of test MEPs, suggesting preserved function of GABAergic intracortical inhibitory interneurons. On the contrary, the subsequent period of MEP facilitation found in normal subjects (ISIs of 6-20 ms) was markedly reduced in patients. This suggests the existence of abnormally prolonged intracortical inhibition or deficient intracortical excitation. In nine patients retested 2 to 4 weeks after the initial seizure, these abnormalities persisted, although to a lesser extent.


CONCLUSIONS
The present findings together with abnormally high motor thresholds could represent protective mechanisms against the spread or recurrence of seizures.
Delvaux
V
V
University Department of Neurology, Hôpital de la Citadelle, B-4000 Liège, Belgium.
Alagona
G
G
Gérard
P
P
De Pasqua
V
V
Delwaide
P J
PJ
Maertens de Noordhout
A
A
D000293:Adolescent; D000328:Adult; D000368:Aged; D016022:Case-Control Studies; D004569:Electroencephalography; D004830:Epilepsy, Tonic-Clonic / Q000175:diagnosis* / Q000209:etiology / Q000503:physiopathology*; D019054:Evoked Potentials, Motor; D005260:Female; D006801:Humans; D008280:Magnetics; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000503:physiopathology*; D015999:Multivariate Analysis; D012008:Recurrence; D013997:Time Factors; D005680:gamma-Aminobutyric Acid / Q000502:physiology
D005680:gamma-Aminobutyric Acid