Abstracts

Unilateral or bilateral asymmetric or symmetric tonic posturing of limbs is usually observed in Supplementary Sensorimotor Area (SSMA) seizures. Our primary objective was to evaluate the reliability of early tonic limb posturing in localizing the seizure generator in patients with SSMA seizures.
Fifty-one patients with medically intractable frontal lobe epilepsy who had stereoencephalographic (SEEG) recordings between January 1993 and January 2003 at the Montreal Neurological Hospital were reviewed. Fourteen patients with typical SSMA semiology were selected. Limb posturing was defined as early when it was the first objective manifestation of the seizures. The mean number of depth electrodes inserted was 6.5 per patient with one at least SSMA explored. Additional epidural electrodes (mean number per patient, 7.6) were used to cover the frontocentral cortex.
Fourteen patients (9 men) with mean age of 24 and mean duration of epilepsy of 18 years at time of evaluation were studied. By definition, all selected patients had early symmetric or asymmetric ictal tonic posturing of limbs. In addition they had somato-sensory aura (42%), tonic contraction of the face (42%), tonic head deviation with or without conjugated eye turning (100%) usually following arm posturing, vocalization (50%), late clonic jerks (64%, unilateral in 1/3) and post-ictal motor deficit (28%). Six patients had MRI abnormalities: a mild left parahippocampal or hippocampal atrophy, 2; diffuse hemispheric atrophy, 1; a small hypointense signal in the right frontal lobe and a right temporal subarachnoid cyst, 1; and focal cortical dysplasia, 2, one in the mid portion of the second frontal gyrus near the anterior aspect of the left SSMA and the other in the right frontal operculum.
Patients were divided into three groups according to SEEG findings: three had focal SSMA onset, and three regional seizure onset with involvement of one SSMA plus adjacent neocortex, and eight diffuse uni- or bilateral seizure onset. Therefore, seizure semiology predicted focal or regional ictal EEG onset in the SSMA in six (43 %) patients. Eleven patients underwent resective or palliative surgery. Eight had a frontal or central cortical resection, but a good outcome (Engel, class Ia) was seen in only three (one from group 1, and two from group 3), two with no SSMA resection and one with an extensive mesial frontal and central removal.
This study showed that early symmetrical or asymmetrical tonic limb posturing has little localizing value, even with the help of other typical clinical manifestations, and does not reliably predict ictal onset in the SSMA. This seizure semiology cannot by itself distinguish patients with ictal onset confined to the SSMA from those with ictal onsets that include the SSMA, or from those in whom seizures originate from adjacent fronto-central compartments.