Analysis of spatio-temporal propagation of occipito-frontal spikes in childhood epilepsies by 3D sequential voltage mapping and dipole localization.

Objective: We sought to study the spatio-temporal propagation of occipito-frontal spikes in childhood epilepsies by voltage mapping and dipole localization and identify types of occipito-frontal spikes based on onset, propagation, and stability of their dipoles.

Methods: Sleep EEG data of children, aged 1-14 years, with a minimum 1 h of recording from June 2018 to June 2021, were analyzed to identify occipito-frontal spikes. In total, 150 successive occipito-frontal spikes were manually selected from each EEG and using a source localization software were averaged using automated pattern matching with a threshold of 80%, and sequential 3D voltage maps of averaged spike were analyzed. Stability quotient (SQ) was calculated as the total number of averages/150. Stable dipole was defined as SQ ≥ .8. Dipole analysis was performed with principal component analysis using an age-appropriate template head model.

Results: Ten children with occipito-frontal spikes were identified; five with self-limited epilepsy with autonomic seizures (SeLEAS) and five with non-SeLEAS epilepsies. Three types of occipito-frontal spikes were identified: (1) narrow occipito-frontal spikes with stable dipoles seen in all five children with SeLEAS which were "apparently" synchronous and bilateral clone-like with an occipito-frontal interval of 10-30 ms and a homogeneous propagation pattern from a unilateral medial parieto-occipital region to an ipsilateral mesial frontal region; (2) wide occipito-frontal spikes with stable dipoles seen in one child with non-SeLEAS and developmental and/or epileptic encephalopathy with spike-wave activation in sleep (D/EE-SWAS) with an occipito-frontal interval of 45 ms, caused by focal spike propagation from a deeper temporal focus to ipsilateral peri-rolandic cortex; and (3) wide occipito-frontal spikes with unstable dipoles seen in four children with non-SeLEAS lesional epilepsies with an occipito-frontal latency of >50 ms and heterogeneous propagation patterns with poor intra-individual dipole stability.

Significance: We successfully identified different types of occipito-frontal spikes in childhood epilepsies. Although the term "occipito-frontal" is used to describe these spikes on the 10-20 EEG system, true propagation from occipital to frontal regions is not necessary. It is possible to differentiate idiopathic from symptomatic cases by analyzing the stability quotient and the occipito-frontal interval of occipito-frontal spikes.