Seizures in small animals Flashcards
What is a seizure?
A transient occurrence of convulsions of focal motor, autonomic or behavioural signs due to abnormal excessive or synchronous epileptic neuronal activity in the brain
Where are seizures localised to?
Forebrain
What other clinical signs can be seen with forebrain lesions
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 deficits on opposite side
Name an excitatory and inhibitory neurotransmitter
Glutamate – EXCITATORY
GABA - INHIBITORY
Describe the pathogenesis of seizures
Imbalance in excitation and inhibition
- Either excessive excitation OR decreased inhibition
- Neurons become hypersynchonised -> Seizure
Name and describe the 4 stages of a seizure
1 = prodrome - any predictive or preceding events
(2 = Aura - initial manifestation of a seizure – from human medicine)
3 = Ictal - seizure event – involuntary muscle tone or movement +/- abnormal sensations or behaviour
4 = Post-ictal - minutes to days. Can have unusual behaviour or neurological deficits e.g. aggressive, blindness
Describe the main features of the ictal event
Usually around 60-90 seconds
Peracute in onset
Characteristics are the same for each event
Occurs most commonly at sleep or rest
Autonomic signs are common
Name the 2 major phenotypic categories of icteral seizures
Generalised
Focal
What are generalised seizures?
Involvement of both cerebral hemispheres simultaneously
CONSIOUSNESS IMPAIRED
What are the phases of generalised seizures?
May have one or several of the following phases:
1. Tonic – clonic
- Extend all 4 limbs
- Extend neck
- Dramatic posture
2. Tonic
3. Clonic
4. Myoclonic - Brief, involuntary shock like
5. Atonic - Complete lack of muscle tone – flop
What is a focal seizure?
Initial activation of ONE part of region in the forebrain
Clinical signs remain unilateral
Name the 3 forms of focal seizures
Motor
Autonomic
Behavioural
What are audiogenic reflex seizures?
Cats
Late onset (median 15 years)
Reflex seizure - seizure that is objectively and consistently precipitated by environmental or internal stimuli e.g. sounds
List the DDx for seizures
Narcolepsy/ cataplexy
Neuromuscular collapse
Syncope
Paroxysmal dyskinesia
Painful episodes
Metabolic disease
Vestibular disease
Idiopathic head tremor syndrome
What are the causes of reactive seizures?
- Seizure occurring as a natural response from the normal brain to a transient disturbance in function
- Concurrent neurological signs usually present
- Metabolic or the result of intoxication
What are the causes of idiopathic epilepsy?
Genetic or presumed genetic in origin
No inter-ictal neurological signs
What are the causes of structural epilepsy?
- Epileptic seizures which are provoked by intracranial or cerebral pathology
- Concurrent neurological signs usually present
- E.g. inflammatory, neoplastic, traumatic
How is idiopathic epilepsy diagnosed?
Diagnosis of exclusion
Dogs between 6 months and 6 years
Normal neurological examination between seizures
When is MRI indicated for dogs with idiopathic epilepsy?
- Age of onset <6 months or >6 years
- Inter-ictal neurological abnormalities consistent with intracranial neurolocalisation
- Status epilepticus or cluster seizure
- Previous presumptive diagnosis of IE and drug- resistance with a single ASD titrated to the highest tolerable dose
When is treatment indicated for epilepsy?
- Structural or metabolic epilepsy
- Status epilepticus or cluster seizures
- An inter-ictal period of 6 months or less
- Post-ictal signs are severe or last longer than 24 hours
- The seizure frequency and/or duration is increasing and/or seizure severity is deteriorating over 3 interictal periods
- The 1st seizure is within 1 month of a traumatic event e.g. RTA
Why is anti-seizure medication not given unless 100% necessary?
Adverse effects
How is epilepsy treated?
- Epilepsy cannot be cured with medication, but drugs are used to symptomatically suppress epileptic seizures
- 3 licenced maintenance treatments in dogs
- No drugs licenced in cats
What are the main considerations regarding epilepsy treatment?
General health of the patient
Owner’s lifestyle
Financial limitations
Owner compliance with the therapeutic regimen
Name the 3 licensed epileptic drugs for dogs
Phenobarbital
Bromide
Imepitoin
Describe the mechanism of action of phenobarbital
Augments the inhibitory effect of GABA - prolonging the chloride channel opening at GABAA receptor
Describe the monitoring needed for phenobarbital use
- 2 weeks after any dose change (inc. haematology, biochemistry)
- 3 months (inc. haematology, biochemistry)
- 6 months (inc. biochemistry)
List the side effects of phenobarbital
- Sedation, ataxia
- Polyuria, polydipsia, polyphagia
- Hepatotoxicity
- Haematological abnormalities (neutropaenia, anaemia, thrombocytopaenia)
- Pseudolymphoma
When is phenobarbital contraindicated?
Contraindicated in dogs with hepatic dysfunction - increased risk of hepatic injury
How is bromide administered to patients?
Usually administered as either potassium (KBr) or sodium (NaBr) salts
When is bromide not licensed?
As a monotherapy
Describe the MOA of bromide
Competes with Cl- transport across nerve cell membranes and inhibits Na+ transport - membrane hyperpolarisation which raises the seizure threshold
Describe the considerations when using bromide in patients
- CONSISTENT DIET
- Monitoring: 12 weeks (inc. haematology and biochemistry)
What are the side effects of bromide?
Sedation
Ataxia and paresis
Bromism (serum concentration >30mmol/L) = toxicity
When is imepitoin not licensed?
Not licenced for use in cluster seizures or structural epilepsy
When is imepitoin licensed?
As a monotherapy
Describe the MOA of imepitoin
Low affinity partial agonist for the benzodiazepine binding site of the GABAA receptor
Describe the metabolism of imepitoin
Metabolised by the liver
Excreted by faecal route
Which anti-epileptic drug doesn’t require monitoring?
Imepitoin
Which anti-epileptic drug can be used off-license in cats?
Phenobarbital
Name 2 off-license antiseizure medications
Levetiracetam
Zonisamide
Name the antiseizure medication of choice for patients with liver disease
Levetiracetam
