Abstracts

Rationale: Inhibitory motor seizures have been classified including atonic seizure, astatic seizures, hypomotor seizures, akinetic seizures, negative myoclonic seizures and aphasic seizures. In contrast with the abrupt falls seen in patients with Lennox-Gastaut syndrome, the head drops in the patients showing axial muscle hypotonia during seizure were slow, taking 2-5 sec to fall down. Which special seizures cover axial muscle hypotonia as semiology? Methods: We included 5 patients with inhibitory motor seizures. There were 2 males and 3 females. We excluded 1 male and 1 female who had aphasic seizures. A long-term video/electroencephalogram (EEG) monitoring, electromyogram (EMG), brain magnetic resonance imaging (MRI) and Single photon emission computed tomography (SPECT) were carried out and compared with previously reported cases. Results: During video/EEG monitoring, patient 1 had 21 habitual seizures, patient 2 had none habitual seizures and patient 3 showed not inhibitory seizure, but bilateral asymmetric tonic seizure. Interictal EEG of Patient 1 showed C3, P3 sharp waves as interictal epileptiform discharges approximately once every 3~5 min during sleep. Ictal semiology consisted of abrupt onset of slow head drop or diminution of neck muscle tone. Consciousness is not impaired, and the neck muscle hypotonia returns to normal by degrees. In all of the seizures recorded by video, patient 1 fell down forward when they occurred while she sat down on the bed, and it took 20 to 30 sec to fall down forward. Ictal EEG started with low-voltage 15- to 18-Hz beta range activities in the vertex areas (Cz maximum), and then repetitive spikes were seen at the centroparietal to vertex area (F4, C4 to Cz), lasting 50-70 sec. (Fig. 1 A) EMG from the neck muscle revealed the neck muscle hypotonia and gradually restoring normal tone. (Fig. 1 B) MRI showed cortical dysplasia involving left parietal lobe. (Fig. 2 A) By using Statistical Parametric Mapping (SPM), the ictal blood flow increase in left parietal lobe. (Fig. 2 B) Conclusions: Neck muscle hypotonia might be a feature of atonic seizures in partial epilepsy. Two possible mechanisms were implicated in atonic seizure development: (1) epileptic activities arising from the premotor areas directly inhibit primary motor cortex or are involved in voluntary movement integration and cannot function during 50-Hz electrical stimulation (negative motor area) or (2) sustained atonia with successive electromyogram (EMG) silent or hypotonic periods caused by epileptic discharges arising from the inhibitory area of the primary sensorimotor area.