epilepsy Flashcards
what is epilepsy?
sudden excessive or synchronous discharge of cerebral cortical neurones
what are the two classifications of epilepsy?
idiopathic:
- no known cause can be identified
symptomatic:
- congenital CNS defects
- cerebrovascular disease
- perinatal or postnatal trauma
- tumours
- CNS infections
what are the two main types of epilepsy?
partial: this involves only local discharge in one area of the brain
generalised: this can involve both hemispheres of the brain
how are partial seizures subdivided? and what are their characteristics?
simple partial: consciousness is preserved (involves frontal cortex)
- motor spasm
-sensory hallucinations
complex partial: consciousness is altered (involves temporal cortex)
- possible automatism
secondary generalised: consciousness is impaired, and the seizures are no longer localised to one area of the brain
how are primary generalised seizures subdivided? and how are they characterised?
tonic clonic:
- a.k.a grand mal
- loss of consciousness
- convulsions
absence:
- brief interruption of consciousness and motor activity
- involves a thalamocortical mechanism
atonic:
- sudden loss of muscle tonic
myoclonic:
- brief contractions of muscle groups
tonic:
- sustained increase in muscle tone
what is status epilepticus? and how is it dealt with?
status epilepticus is continuous seizures which are not separated by time, and are not self limiting. this can involve metabolic and neuronal damage.
usually clonazepam is given intravenously
how does epilepsy arise?
results from abnormal, hyper excitable neurones.
those neurones undergo, repetitive depolarizations called paroxysmal depolarisation shifts, PDS
- those are caused by changes in the intrinsic properties of the neurones including
- sustained supra threshold depolarisation (due to entry of sodium and calcium)
- normally the entry of calcium currents would cause an entry of potassium currents (which would cause hyper polarisation
- the failure of the entry of calcium dependant potassium currents is crucial for the transformation from interictal spike to PDS
what is the mechanism of action of most anti-epileptic drugs?
they inhibit sodium channels in hyper excitable cells without affecting normal electrical activity. those drugs decrease the activity of voltage gates in hyper excitable cells, because the preferentially bind to inactivated sodium channels (aka use dependant block)
how does ethosuxamide work?
inhibits calcium channel voltage gates in the thalamus (THE T-TYPE)
hence very good to use in absence seizures
what is the mechanism of action of sodium valproate
inhibits GABA metabolism after uptake
also inhibits sodium channels
effective against most forms of epilepsy
what is the mechanism of action of vigabatrin?
irreversible selective GABA transaminase inhibtior, reduces GABA metabolism
- more effective in partial than generalised seizures
- may exacerbate absence seizures
what is the mechanism of action of Gabapentin?
blocks calcium gated voltage channels
effective against partial and generalised seizures
what is the best treatment option for partial seizures?
carbemazepine
and valprotate and phenytoin
what is the best treatment option for generalised tonic clonic?
valproate
and carbemazepine
what is the best treatment option for generalised absence?
ethosuximide
