Mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) with high-frequency oscillations on scalp EEG: A case report

Mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) is a rare mitochondrial disease with a prevalence of 16-18 per 100,000 persons. Most patients with MELAS develop epilepsy and require effective control of recurrent attacks. High-frequency oscillations (HFOs) on scalp EEG are transient bursts of EEG activity with frequencies beyond 80 Hz and are a promising biomarker for seizure control in epilepsy. However, reports on scalp HFOs are limited to some epilepsy syndromes. Herein, we report on the appearance of scalp HFOs in a pediatric patient with MELAS. The patient, a 13-year-old boy, presented with a stroke-like episode at age 9 years and was diagnosed with MELAS. The main symptom was visual disturbances, but epilepsia partialis continua (EPC) was also observed. Scalp EEG recordings were made six times: 8 days before the stroke-like episode (day -8 EEG), the day of appearance (day 1 EEG), and 4, 8, 10, and 100 days after the episode. Analysis of scalp HFOs showed that no scalp HFOs were detected in the day -8 EEG, whereas 1.20 scalp HFOs per minute were detected in the day 1 EEG at the appearance of the stroke-like episode with EPC. The scalp HFO detection rate decreased with the loss of EPC, and no scalp HFOs appeared on EEG, although visual disturbances continued to be observed. By contrast, epileptic discharges remained on EEG after EPC disappearance. Scalp HFOs have the potential to be a useful biomarker for reflecting epileptic seizure in patients with MELAS.