Seizures in small animals

Question 1

What is a seizure?

Answer 1

A transient occurrence of convulsions of focal motor, autonomic or behavioural signs due to abnormal excessive or synchronous epileptic neuronal activity in the brain

Question 2

Where are seizures localised to?

Answer 2

Forebrain

Question 3

What other clinical signs can be seen with forebrain lesions

Answer 3

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

Question 4

Name an excitatory and inhibitory neurotransmitter

Answer 4

Glutamate – EXCITATORY
GABA - INHIBITORY

Question 5

Describe the pathogenesis of seizures

Answer 5

Imbalance in excitation and inhibition
- Either excessive excitation OR decreased inhibition
- Neurons become hypersynchonised -> Seizure

Question 6

Name and describe the 4 stages of a seizure

Answer 6

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

Question 7

Describe the main features of the ictal event

Answer 7

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

Question 8

Name the 2 major phenotypic categories of icteral seizures

Answer 8

Generalised
Focal

Question 9

What are generalised seizures?

Answer 9

Involvement of both cerebral hemispheres simultaneously
CONSIOUSNESS IMPAIRED

Question 10

What are the phases of generalised seizures?

Answer 10

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

Question 11

What is a focal seizure?

Answer 11

Initial activation of ONE part of region in the forebrain
Clinical signs remain unilateral

Question 12

Name the 3 forms of focal seizures

Answer 12

Motor
Autonomic
Behavioural

Question 13

What are audiogenic reflex seizures?

Answer 13

Cats
Late onset (median 15 years)
Reflex seizure - seizure that is objectively and consistently precipitated by environmental or internal stimuli e.g. sounds

Question 14

List the DDx for seizures

Answer 14

Narcolepsy/ cataplexy
Neuromuscular collapse
Syncope
Paroxysmal dyskinesia
Painful episodes
Metabolic disease
Vestibular disease
Idiopathic head tremor syndrome

Question 15

What are the causes of reactive seizures?

Answer 15

• 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

Question 16

What are the causes of idiopathic epilepsy?

Answer 16

Genetic or presumed genetic in origin
No inter-ictal neurological signs

Question 17

What are the causes of structural epilepsy?

Answer 17

• Epileptic seizures which are provoked by intracranial or cerebral pathology
• Concurrent neurological signs usually present
• E.g. inflammatory, neoplastic, traumatic

Question 18

How is idiopathic epilepsy diagnosed?

Answer 18

Diagnosis of exclusion
Dogs between 6 months and 6 years
Normal neurological examination between seizures

Question 19

When is MRI indicated for dogs with idiopathic epilepsy?

Answer 19

• 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

Question 20

When is treatment indicated for epilepsy?

Answer 20

• 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

Question 21

Why is anti-seizure medication not given unless 100% necessary?

Answer 21

Adverse effects

Question 22

How is epilepsy treated?

Answer 22

• 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

Question 23

What are the main considerations regarding epilepsy treatment?

Answer 23

General health of the patient
Owner’s lifestyle
Financial limitations
Owner compliance with the therapeutic regimen

Question 24

Name the 3 licensed epileptic drugs for dogs

Answer 24

Phenobarbital
Bromide
Imepitoin

Question 25

Describe the mechanism of action of phenobarbital

Answer 25

Augments the inhibitory effect of GABA - prolonging the chloride channel opening at GABAA receptor

Question 26

Describe the monitoring needed for phenobarbital use

Answer 26

- 2 weeks after any dose change (inc. haematology, biochemistry) - 3 months (inc. haematology, biochemistry) - 6 months (inc. biochemistry)

Question 27

List the side effects of phenobarbital

Answer 27

- Sedation, ataxia - Polyuria, polydipsia, polyphagia - Hepatotoxicity - Haematological abnormalities (neutropaenia, anaemia, thrombocytopaenia) - Pseudolymphoma

Question 28

When is phenobarbital contraindicated?

Answer 28

Contraindicated in dogs with hepatic dysfunction - increased risk of hepatic injury

Question 29

How is bromide administered to patients?

Answer 29

Usually administered as either potassium (KBr) or sodium (NaBr) salts

Question 30

When is bromide not licensed?

Answer 30

As a monotherapy

Question 31

Describe the MOA of bromide

Answer 31

Competes with Cl- transport across nerve cell membranes and inhibits Na+ transport - membrane hyperpolarisation which raises the seizure threshold

Question 32

Describe the considerations when using bromide in patients

Answer 32

- CONSISTENT DIET - Monitoring: 12 weeks (inc. haematology and biochemistry)

Question 33

What are the side effects of bromide?

Answer 33

Sedation Ataxia and paresis Bromism (serum concentration >30mmol/L) = toxicity

Question 34

When is imepitoin not licensed?

Answer 34

Not licenced for use in cluster seizures or structural epilepsy

Question 35

When is imepitoin licensed?

Answer 35

As a monotherapy

Question 36

Describe the MOA of imepitoin

Answer 36

Low affinity partial agonist for the benzodiazepine binding site of the GABAA receptor

Question 37

Describe the metabolism of imepitoin

Answer 37

Metabolised by the liver Excreted by faecal route

Question 38

Which anti-epileptic drug doesn't require monitoring?

Answer 38

Imepitoin

Question 39

Which anti-epileptic drug can be used off-license in cats?

Answer 39

Phenobarbital

Question 40

Name 2 off-license antiseizure medications

Answer 40

Levetiracetam Zonisamide

Question 41

Name the antiseizure medication of choice for patients with liver disease

Answer 41

Levetiracetam