Conversely, medications that increase GABA-B activity (e.g., vigabatrin) exacerbate the frequency of absence seizures. Medications that suppress T-type calcium channels, such as ethosuximide and valproate, are effective anti-absence drugs. Īs explained by the genetics of absence epilepsy, genes coding for T-type calcium channels and for GABA receptors have been associated with the etiopathogenesis of this type of epilepsy. Therefore, abnormal oscillatory rhythms can originate from T-type channel abnormalities or from increased GABA-B activity. Reactivation requires a relatively long hyperpolarization facilitated by GABA-B receptors. After depolarization, T-type channels briefly allow calcium inflow before becoming inactivated. These are mediated through low-threshold transient calcium channels known as T-type channels. Shifts between these two firing patterns in the thalamic nucleus reticularis are modulated by spikes in thalamocortical networks and neurons from the thalamic nucleus reticularis. Neurons from the thalamic nucleus reticularis can fire in an oscillatory pattern (for example, rhythmic bursts involved in the generation of sleep spindles) or continuously in single spikes (tonic firing during wakefulness). Neurons from the thalamic nucleus reticularis containing inhibitory GABA-ergic projections that connect with other neurons from the same nucleus and with thalamic relay neurons these neurons do not connect directly with the cortex The International League Against Epilepsy Classification of 2017 defines absence seizures as “generalized non-motor seizures.” However, this term is not entirely precise because, as discussed below, motor manifestations of absence epilepsy are frequently seen. Historically, absence epilepsy was known as “pyknolepsy.” This term originates from the Greek term pyknos, which means “very frequent” or “grouped.” The term “petit mal” seizure was once used to describe an absence seizure in the past, but it is no longer encouraged. Absence seizures are brief seizures characterized by a behavioral arrest that correlates with generalized 3-Hertz spike-and-wave discharges on electroencephalogram (EEG.) Absence seizures occur in multiple genetic generalized epilepsies, including childhood absence epilepsy (CAE), juvenile absence epilepsy (JAE), and juvenile myoclonic epilepsy (JME.) Atypical absence seizures have been reported in up to 60% of patients with Lennox-Gastaut syndrome.
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