Epilepsy Flashcards
Define seizure
Clinical manifestation of abnormally excessive & hyper synchronous activity of neurons located mainly in cerebral cortex
How are seizures classified?
- Generalized= initial activation of neurons throughout both hemispheres
- Partial= initial activation of limited number of neurons in part of 1 hemisphere
- Secondary generalized= partial seizure that spreads to involve majority of 2 cerebral hemispheres
What are the manifestations of a partial seizure in the different lobes?
- Frontal= Jacksonian seizure- tingling in hand/arm, adverse seizures- eyes/head turn to one side
- Parietal= tingling/jerking of leg, arm, face
- Occipital= flashing lights/spots, vomiting
- Temporal= smell/taste, altered behaviour, deja vu, lip smacking, chewing movements
What is status epilepticus?
- Life threatening
- Brain in state of persistent seizure= 30+mins OR 2+ without full recovery
- Confers greater risk for future unprovoked seizures
What is the mechanism of a seizure?
- Excitation= ionic: Na+, Ca2+ influx, neurotransmitter: aspartate & glutamate release
- Inhibition= Ionic: Cl-, K+ efflux, neurotransmitter: GABA release
- Either can result in too much neuronal activity-seizure
- Initially localised hyper excitability spreads to surrounding neuronal networks
- Either inhibited or chain reaction-seizure
What is the function of inhibitory interneurons?
- Allow activity to spread in one direction but not sideways
- Release neurotransmitter GABA
Describe GABA
- γ-aminobutyric acid
- Major inhibitory neurotransmitter
- GABA(A)= ligand gated chloride channel receptor
- GABA(B)= G protein-coupled receptor
What types of epilepsy are caused by a mutation in GABA(A) receptor subunits?
- Childhood absence epilepsy
- Pure febrile seizures
- Juvenile myoclonic epilepsy
- Generalized epilepsy with febrile seizures
- Dravet syndrome/ SMEI
What are the modes of action for anti-epileptic drugs?
- Suppress a.p= Na channel blocker, K channel opener
- Enhance GABA transmission= GABA mimetics/uptake inhibitor
- Suppression of excitatory transmission= glutamate receptor antagonist
Name some Benzodiazepines and describe them
- Clonazepam= generalized tonic-clonic, absence & partial seizures
- Clorazepate= partial seizures
- Diazepam/valium/lorazepam= SE given IV
What is the mechanism of action for benzodiazepines
- Inc affinity of GABA for receptor
- Inc Cl- current
- Suppresses seizure focus by raising ap threshold
- Strengthens surrounding inhibition-prevents spread
What are the negatives of using benzodiazepines?
- Sedation major side effect
- Problems with tolerance & dependance (avoid LT use)
- Respiratoy depression in IV use
What is the mechanism of action for Phenytoin?
-When Na+ channels inactivated after depolarisation it binds to receptor so slows down recovery
Describe epilepsy & pregnancy
- Very harmful to pregnant women
- Folic acid recommended
- Phenytoin/ valproic acid contraindicated
What anti-epileptic drugs have mixed actions?
- gabapentin
- valproate (valproic acid)= tonic-clonic & absence, also used in bipolar
