Typical Absence (Petit Mal) Seizure Hyperventilation: A common trigger of absence seizures
in pediatric patients with existing absence seizures ↑ respirationà↑ CO2 expelled from body & blood
↓ acidic CO2 levels in bloodà↑ blood pH (↓ blood acidity)
Predisposes neurons to fire spontaneously and asynchronouslyà↓ seizure threshold
Pathogenesis of absence seizure is complex and not yet fully elucidated, but evidence supports the cortical focus theory:
Hyperexcitable focal neurons on cerebral cortex send activation signals down to thalamocortical neuron network
Activated neurons in thalamus interact with cortical neurons to produce rhythmic oscillatory neuronal firing (brain waves) between these two regions of the brain
Abnormal rhythmic and bilaterally synchronous activation of the cerebral cortex during wakefulness
Between seizures (inter-ictal)
Inter-ictal changes in neuronal firing patterns and connectivity in sensorimotor cortices (mechanism unclear)
First degree relative with absence epilepsy
Genetic predisposition/idiopathic (>90%)
No single identified cause such as a structural lesion or single genetic mutation
Multiple gene mutations that predispose to epilepsy when occurring together
Authors: Alyssa Federico, Davis Maclean, Erika Russell, Harjot Atwal Reviewers: Ario Mirian, Shaily Singh*, Kim Smyth*, Yan Yu* * MD at time of publication
Monogenetic mutation (<10%) Single gene mutation predisposing to epilepsy Mutations involve genes encoding voltage-gated calcium channels and gamma aminobutyric acid (GABA) receptors, which are important in regulating thalamocortical activity Absence Seizure: Brief lapse of consciousness with a vacant stare lasting 3-10 seconds, without convulsions or loss of motor tone. May occur up to 100 times per day. Seizure features (ictal phase) Absence seizures generally occur in the context of an epilepsy syndrome and present in childhood Childhood absence epilepsy: Most common form of pediatric epilepsy, characterized by absence seizures Juvenile absence epilepsy: Characterized by absence seizures +/- generalized tonic-clonic seizures Juvenile myoclonic epilepsy: Characterized by myoclonic seizures +/- absence seizures Post-seizure (post-ictal) Mechanisms unclear Consciousness regained immediately after seizure No post-ictal symptoms No memory of event Neuropsychiatric symptoms (poor attention, memory, mood, cognition) seen in 60% of children Smooth/rapid transition to seizure No aura (warning sign) prior to seizures Seizure activity directly or indirectly impairs communication between neural networksà alters activity of brain structures involved in maintaining awareness Some simple response to internal or external stimuli may remain intact (mechanisms unclear) Automatisms: Eye movements (fluttering), oral (lip smacking, swallowing, chewing), manual (finger tapping, scratching) Brain wave oscillations generated in the thalamus EEG findings: Generalized 3 Hz spike-wave activity with maximum amplitude in both frontal lobes Impaired awareness Inhibition of response to external stimuli Impaired school performance and social interactions Legend: Pathophysiology Mechanism Sign/Symptom/Lab Finding Complications Published January 2, 2021 on www.thecalgaryguide.com