Flashcards in Epilepsy Deck (74)
What are seizures?
Clinical manifestation of an abnormally excessive and hypersynchronous activity of neurones located predominantly in the cerebral cortex (ie. excessive neuronal firing)
Why do convulsions occur?
The cortical discharges from the excessive neuronal activity of the seizures can be transmitted to the muscles causing twitches or convulsions
Do seizures always manifest in the same way?
No, epileptic seizures manifest in different ways depending on their site of origin
What are the 3 main classifications of seizures - what does each refer to?
Based on the origin and spread of activity
1) Generalised - with initial activation of neurons throughout both hemispheres
2) Partial - with initial activation of a limited number of neurons in a part of one hemisphere
3) Secondary generalised - a partial seizure that later spreads to involve the majority of the 2 cerebral hemispheres
What is a myoclonic seizure?
Jerking movements of the body
What is a tonic-clonic seizure?
Stiffening, falling and jerking of the body
What is an atonic seizure?
Falling heavily to the ground
What is an absence seizure?
Staring and blinking without falling
What are the 5 sub-types of generalised seizure?
What are the types of partial seizures - what does each refer to?
1) Simple - seizure activity whilst the person is alert
2) Complex - Seizure activity with change in awareness of surroundings
3) With secondary generalisation - seizure activity begins in one area and spreads
What is the manifestation of a partial seizure originating in the parietal lobe?
Tingling in or jerking of arm, leg and face
What is the manifestation of a partial seizure originating in the frontal lobe?
Jacksonian seizure (tingling feeling in the hand or arm)
What is the manifestation of a seizure beginning in the frontal lobe?
Adversive seizures - eyes or head both turn to one side
What is the manifestation of a seizure beginning in the occipital lobe?
Flashing lights or spots, vomiting
What is the manifestation of a seizure originating in the temporal lobe?
Strange smell or taste, altered behaviour, de ja vu, lip smacking or chewing movements
What does electroencephalography (EEG) do?
Scalp electrodes record the electrical activity along the scalp produced by the firing of neurones within the brain - this converts the electrical impulses into waves (Spike-wave discharges) which can be monitored and analyzed
What is the difference in appearance of a partial and generalized seizure on EEG?
Partial - only half of the electrodes show the amplified waves of excessive activity
Generalised - all of the electrodes show the amplified waves of excessive activity
What is status epilepticus?
Life threatening condition in which the brain is in a state of persistent seizure - more than 30 mins continuous seizure activity or 2 or more sequential seizures spanning this period without full recovery between seizures
Why is status epilepticus a medical emergency?
Its a medical emergency because the longer the seizure lasts, the less likely it is to stop on its own. SE confers greater risk for future unprovoked seizures
How is epilepsy defined?
Epilepsy can be defined as a condition in which seizures recur, usually spontaneously; a single seizure episode is not considered as epilepsy - ie. need 2 or more unprovoked seizure
What are the 2 basic mechanism underlying seizures?
1) Excitation (too much)
- Ionic - Na+, Ca2+ influx
- Neurotransmitter - glutamate, aspartate release
2) Inhibition (too little)
- Ionic - Cl- influx, K+ efflux
-Neurotransmitter - GABA release
Either situation can result in too much neuronal activity and cause a seizure
What neurons are involved in preventing seizures physiologically, how?
Inhibitory interneurons - allow activity to spread in one direction, but not to spread out sideways
They do so by releasing the inhibitory neurone GABA
How are interneurones involved in the manifestation of a seizure?
Have initial localized hyperexcitability which spreads into surrounding neuronal networks - this may be counterbalanced by inhibitory mechanisms or, after involving more and more neurones, can cause a clinically visible seizure
What is GABA, where is it found?
Major inhibitory neurotransmitter - found at ~30% of synapses
What are the 2 GABA receptors and what kinds are they?
GABAa - ligand-gated chloride channel receptor
GABAb - G protein-coupled receptor
What is the structure of GABAa receptor?
Pentameric - typical in vivo subunit composition is 2 alpha, 2 beta and 1 gamma or delta subunit
How can GABAa receptor structure affect drug therapies?
GABAR subunit composition determines the intrinsic properties of each channel - different subunits have different affinities for different drugs
What are the 5 currently known epilepsies caused by GABAa receptor mutations?
1) CAE - childhood absence epilepsy
2) FS - pure fibrile seizures
3) GEFS+ - generalised seizures with febrile seizures plus
4) JME - juvenile myoclonic epilepsy
5) DS - dravet syndrome (also known as SMEI - severe myoclonic epilepsy in infancy)
How many transmembrane domains does each GABA receptor subunit have?