Abstracts

RATIONALE: The syndrome of hypothalamic hamartoma (HH) and gelastic epilepsy (GE) has been proposed as a model for symptomatic generalized epilepsy (SGE), with spike-wave (SW) and decremental EEG patterns and mixed generalized seizures developing in an age-dependent fashion in many patients.
METHODS: Of 17 children with intractable GE who underwent detailed neurological evaluation prior to transcallosal resection/disconnection of HH at our center since 1997, 12 (age 4-17 yrs) had features of SGE defined as the presence of tonic and other generalized seizures, abundant interictal SW, generalized decremental or fast ictal rhythms, and neurobehavioral disturbance. Interictal scalp EEG recordings were performed 1-113 weeks (median 1) before and 1-17 weeks (median 2) after surgery. Interictal SW was measured as a percentage (SW%) of 5-minute samples of awake and asleep EEG for each patient, and the preoperative and first postoperative EEGs compared. In 7 patients, intraoperative EEG was recorded by depth electrode from the HH prior to resection and simultaneously from the frontotemporal scalp and exposed frontal cortex before, during and after resection.
RESULTS: Onset of gelastic seizures was at 0-18 mths (mean 3); 6 had neonatal onset. Complex partial features developed between 0.3-7 yrs (mean 4) and tonic features between 1-9 yrs (mean 6). 11 had normal development in the first year of life. Preoperatively, intellectual impairment was present in all and behavioral disturbance in 9. Several children had normal EEGs in early life. Preoperatively, all had abundant interictal SW, with slow SW in 9 and continuous SW during sleep in 5. SW was recorded intraoperatively over the scalp and cortex before, during and after HH resection in 6/7 cases. None of the HH depth recordings showed SW or other epileptiform patterns. Postoperatively (mean follow-up 15 mths), tonic seizures ceased in 10 patients and 5 are seizure free. Early behavioral improvement (e.g. alertness and speech) occurred in all and continued in 10. SW activity was markedly reduced in 9 patients awake and in 7 asleep. Mean SW% for the group decreased from 14% to 4% awake and from 43% to 19% asleep. All 6 in whom awake SW was abolished had cessation of tonic seizures and sustained behavioral improvement; later EEGs performed at 4-41 mths in 3 showed continued absence of SW.
CONCLUSIONS: Resolution of SGE clinical features after HH resection is associated with a marked reduction in interictal SW activity, which may be the basis of the neurobehavioral improvements. Whereas seizures in this syndrome arise from the HH, interictal SW does not and is most likely a secondary thalamocortical phenomenon.
Support: Dr Freeman is supported by a Trainee Research Scholarship from the Murdoch Childrens Research Institute and by a Faculty Research Scholarship from the University of Melbourne, Faculty of Medicine, Dentistry and Health Sciences (Department of Paediatrics).