Epilepsy Flashcards
Define seizures
Seizures are temporary abnormal electro-physiological phenomena of brain, resulting in abnormal synchronisation of electrical neuronal activity
Term can be used for any sudden, short lasting & transient event
2 types: focal & generalised
Define epilepsy
Epilepsy is disease of brain characterised by enduring predisposition to create epileptic seizures
At least 2 unprovoked seizures >24 hours apart
Define convulsions
Convulsions are sudden & violent motor activity of cerebral or brainstem origin
May also occur in absence of electrical cerebral discharge
e.g. response to hypotension, hypoxia
Not all epileptic seizures cause convulsions
What are the causes of convulsions
Discontinuation of antiepileptic drugs
Idiopathic epilepsy
Anorexia, metabolism, hemorrhage, systemic infection, tumor, trauma, drugs, CNS infection, congenital
How does epilepsy work
Epilepsy is characterised by recurrent episodes of paroxysmal (sudden & uncontrolled) brain dysfunction due to sudden, disorderly & excessive neuronal discharge
At level of single neurons, epileptiform activity consists of sustained neuronal depolarisation resulting in burst of action potentials, a plateau-like depolarisation associated with completion of action potential burst, rapid repolarisation followed by hyperpolarisation
Sequence is called paroxysmal depolarising shift
Bursting activity from prolonged depolarisation is due to influx of extracellular Ca2+
Leads to opening of voltage-dependent Na+ channels, influx of Na+ & generation of repetitive action potentials
Subsequent hyperpolarisation is mediated by GABA receptors & Cl-/K+ efflux
What are focal seizures
Abnormal electrical activity arises in localised groups of neurons or network within one hemisphere
Clinical signs reflect functions of areas involved
Motor:
Lip smacking, chewing, licking, teeth grinding, swallowing, running movement
Autonomic:
Dilated pupils, hypersalivation, vomiting
Behavioural:
Anxiousness, restlessness, unexplainable fear reactions, abnormal attention seeking
What is status epilepticus
Neurological emergency
Conscious epileptic seizure activity lasting longer than 5 min or 2+ with incomplete recovery or consciousness
What is the epilepsy treatment
Epileptic seizures caused by imbalance of inhibitory & excitatory activity in brain
Anticonvulsive drugs restore balance, predominantly by facilitation of inhibitory activity
Treatment works by:
Altering intrinsic membrane properties (primarily Na+ channels)
Increasing inhibitory transmitter function (GABA system)
Decreasing excitatory transmitter function (glutamate system)
Describe barbiturates in epilepsy treatment
Bind to GABA receptor to increase its power
Metabolised by liver
Long half life
Drug of choice in dogs & cats
Least toxic, least expensive & most use
Describe BZD in epilepsy treatment
Bind to GABA receptors
Metabolised by liver
Limited toxicity
Diazepam is drug of choice in all animals for status epilepticus
