Lateralized periodic discharges and photic sensitivity in adult onset MELAS syndrome in twin sisters.

Mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome is one of the most common mitochondrial disorders, typically presenting with symptoms before the age of 40. Epileptic seizures are a common manifestation, with both focal and generalized seizures being observed. EEG findings can be variable, with the most common patterns being slow background activity followed by epileptiform discharges.Here, we present monozygotic twin sisters with late-onset MELAS and specific EEG features, including lateralized periodic discharges and sensitivity to photic stimulation, which have been rarely reported in the literature. These cases emphasize the importance of considering MELAS in the differential diagnosis of late-onset symptoms. Furthermore, EEG findings such as sensitivity to photic stimulation may contribute to understanding MELAS pathophysiology, even during asymptomatic periods.