Investigators from the Hospital for Sick Children, Toronto, Canada, and Okayama University Hospital, Japan, analyzed the high occurrence rate (OR) of interictal high frequency oscillations (HFOs) at 80-200 Hz (ripples) and >200 Hz (fast ripples, FRs). The resection ratios of high-OR ripples and high-OR FRs showed significant correlations with seizure outcome (p=0.038 and 0.048, respectively). Multiple extensive zones with high-OR HFOs suggest a complex and widespread epileptic network in TSC. In patients with drug-resistant epilepsy, resection of cortex with both interictal high-OR ripples and high-OR FRs on IVEEG correlated with a good seizure outcome. [1]

COMMENTARY. A previous study by investigators at the Royal Children's Hospital, Melbourne, Australia, found interictal FR involved tubers in TSC more commonly than perituberal cortex but were not associated with electroclinically distinct seizures (EDS). Tubers play a greater role in seizure genesis than perituberal cortex, suggesting that tuberectomy may be a sufficient surgical approach in a number of TSC patients with seizures. Ictal fast rhythms at seizure onset were confined to tubers in 73% and involved tuber with perituberal cortex in 27% [2].

In a subset of TSC patients, the distribution of the epileptogenic zone propagates with time from a single focus at the onset of seizures to bilateral and multiple foci. The laterality of spikes during REM sleep on video EEG monitoring correlates with the epileptogenic hemisphere. The video EEG and MEG are helpful in identifying the epileptogenic zone among multiple cortical tubers [3].