Neurology: Seizures Flashcards
What is a seizure?
A transient occurrence of convulsions or focal motor, autonomic or behavioural signs due to abnormal excessive or synchronus epileptic neuronal activity in the brain
Where in the brain causes a seizure?
Forebrain activity change
What are other possible changes with forebrain localisation?
Other then seizures
- Behaviour change
- Compulsive circling or pacing
- Head turn on same side as the lesion
- Loss of vision on opposite side as the lesion
- Postural reaction defecits on opposite side
What is the pathogenesis of seizures?
Multifactorial
Imbalance in exitation and inhibition
* Either excessive exitation or decreased inhibition
Glutamate- exitatory
GABA- inhibitory
Neurons become hypersynchronised- seizure
What are the stages of a seizure?
- Prodrome- any preditive or preceding events
- Aura- initial manifestation of a seizure
- Ictal- seizure event- involuntary muscle tone or movement ± abnormal sensations or behaviour
- Post-ictal- minutes to days- can have unusual behaviour or neurological deficits
- How long does ictal event last
- When does it most commonly occur?
- What are the two major phenotypic categories?
- 60-90 seconds
- Sleep or rest
- Generalised, focal
Autonomic signs are common- hypersalivate, urinate, defecate
What parts of the brain are involved in generalised seizures?
- Involvment of both cerebral hemispheres simultaneously
- Consciousness impaired
What different phases may be involved in a generalised seizure?
- Tonic- clonic- extent all 4 limbs
- Tonic
- Clonic- repetitive muscle movement
- Myoclonic- shock like contractions
- Atonic- complete lack of muscle tone
Tonic- clonic most common
What part of the brain is involved in focal seizures?
What are the forms of focal seizures?
- Initial activation of one part of region in the forebrain
- Clinical signs remain unilateral
Forms
* Motor- twitching ear, facial automations
* Autonomic- pupils dilated, hypersalivation
* Behavioural
What is audiogenic reflex seizure?
How is it treated?
- Reflex seizure that is objectively and consistently precipitated by environmental or internal stimuli
- Myoclonic seizures progressing to generalised tonic-clonic seizures
Cats- late onset
Levetiracetam typically effective
What are the differentials for a seizure?
- Narcolepsy/cataplexy
- Neuromuscular collapse
- Syncope
- Paroxysmal dyskinesia
- Painful episodes
- Metabolic disease
- Vestibular disease
How is idiopathic head tremor syndrome treated?
Stress causes
Distraction stops- stoke, treat
What breed is affected by episodic hypertonicity?
CKCS
- Increased muscle tone in all 4 limbs
Tx
* benzodiazipine- clonazepam
What is paroxsysmal dyskinesia?
Spikes disease, paraosysmal gluten-sensitive dyskinesia (border terriers)
- Disconected movements
- Dysponesia
- Not painful- mins to hours
Clonazepam
What- broadly- are the three causes of seizures?
Reactive
* Natural response from the normal brain to a transient disturbance in function
* Concurrent neurological signs usually present
* Metabolic or intoxication
Idiopathic
* Genetic or presumed genetic in origin
* No inter-ictal neurological signs
Structural epilepsy
* Epileptic seizures which are provoked by intracranial or cerebral pathology
* Concurrent neurological signs usually
* Inflammatory, neoplastic, traumatic
What are the different causes of seizures?
- V- ischaemic encephalopathy, cerebrovascular accident
- I- MUO
- T- traumatic brain injury, toxicity
- A- congenital malformation
- M- hepatic enceph, renal enceph, hypoglycaemia
- I- idiopathic
- N- entra or intraparenchymal neoplasia
- D- lafora disease, NCL
How is idiopathic epilepsy diagnosed?
- Diagnosis of exclusion
- Dogs between 6 months and 6 years
- Normal neurologicl examination between seizures
A- idipathic- genetic epilepsy
* Lagotto romagnlolo
* Belgian shepherd
* Boerboels
B- idiopathic- suspected breed epilepsy
* genetic influence with high breed prevalence
C- idiopathic- unknown cause
* epilepsy in which the nature of the underlying cause is as yet unkown
* no indication of structural epilepsyq
When is an MRI appropriate?
- Age of onset <6 m or <6 years
- Inter-ictal neurological abnormalities consistent with intracranial neurolocalisatoin
- Stratus epilepticus or cluster seizure
- Previous presumptive diagnosis of IE and drug resistance
When is starting treatment indicated?
- Structural or metabolic epilepsy
- Status epilepticus or cluster seizures
- An inter-ictal period of 6 m or less
- Post- ictal signs are severe or last over 24h
- Frequency is increasing
- Severity worsening
- 1st seizure within 1 months of traumatic event
What are the three anti epileptic treatments?
- Phenobarbital
- Bromide
- Imepitoin
not licensed- levetiracetam, zonisamide,
- What is the mechanism of phenobarbital?
- How does it need to be monitored?
- What are the side effects?
- How is it metabolised?
- Augments the inhibitory effect of GABA- prolongs chloride channel opening at GABA
- 2 weeks, 3 months, 6 months (haem/biochem)
- Sedation, ataxia, polyuria, hepatotoxicity, haem abnormalities, pseudolymphoma
- Hepatic microsomal enzymes- induces cytochrome P450 activity
Care with hepatic dysfunction
- What is the mechanism of action of bromide?
- When should it be monitored?
- What are the side effects?
- How is it metabolised?
KBr or NaBR
- Competes with Cl- transport across nerve cell membranes- inhibits Na+ transport
- 12 weeks
- Sedation, ataxia, paresis, bromism (toxicity)
- Excreted unchanged in urine- undergoes tubular reabsorption in competition with chlorine
- What is the MAO of imepitoin?
- How is it monitored?
- What are the side effects?
- How is it metabolised?
- Low affinity partial agonist site of GABA receptor
- None
- Phenobarb but fewer
- Liver excreted by faecal
- What is the action of levetiracetam?
- What is the action of zonisamide?
- Reduced intracellular Ca2+ accumulation
- Blocks propogation of epileptic dishcharges- spenny
Levetiracetam fast working- good for liver disease
How are seizures treated in cats?
- No licenced medication
- Diazepam- fulminant hepatic necrosis rare but associated with oral administration
- Phenobarbitone
- Potassium bromide- avoid
- Propofol- heinz body anaemia
