EEG, clinical, and MRI features of status epilepticus associated with mitochondrial diseases

This study aimed to identify specific EEG features of status epilepticus (SE) in patients with mitochondrial diseases and correlate them with clinical and neuroimaging findings.

Clinical, EEG, and brain MRI data from adult patients with mitochondrial-related SE treated at Pitié-Salpêtrière hospital between 2010 and 2021 were reviewed.

Thirteen patients were included, with MELAS (n = 5), POLG (n = 3), MERRF (n = 2), COQ8A (n = 2), and MT-ND1 variant (n = 1). One patient had two distinct SE episodes, totaling 14 episodes. Three main EEG patterns were identified: Type 1 (rhythmic sequences with definite evolution, n = 6), Type 2 (Lateralized Periodic Discharges with plus-modifiers (LPDs-plus) and clinical ictal manifestations, n = 12), and Type 3 (LPD-plus evolving into rhythmic activities, n = 11). MRI findings revealed FLAIR hyperintensities indicative of stroke-like lesions in 12 patients (onset: 4-28 days). In three cases, initial MRI was normal, with delayed hyperintensities (5-35 days). In 11/12 cases, stroke-like lesions were confirmed using perfusion or ASL. The localization of these lesions corresponded to electroclinical presentation of SE in most cases. In two patients, the spatial distribution of FLAIR hyperintensities did not align with EEG findings. Evolution of EEG patterns was seen during SE in 12 out of 14 episodes: Type 1 to Type 2 (n = 3), Type 2 to Type 3 (n = 6), and Type 1 to Type 2, then Type 3 (n = 3).

SE is a severe complication of mitochondrial diseases. Three main EEG patterns were identified across episodes. Correlation with MRI suggests two mechanisms: (i) neuronal dysfunction generate rhythmic SE patterns that subsequently induce stroke-like lesions, due to increased local energy demands, and (ii) in more severe cases, acute bioenergetic failure and stroke-like lesions may directly trigger a specific EEG pattern, prolonging SE duration.