Seizures and Anti-epileptic Drug Management in the Dog and Cat Flashcards
Define a seizure
A seizure is a clinical manifestation of excessive or hypersynchronous abnormal electrical activity in the brain
What are the 4 components to a seizure?
- Prodrome: the time before the seizure begins (hours to days), the owner may report unusual behaviour e.g. restlessness or anxiety
- Aura: the time immediately before a seizure when the animal exhibits stereotypical sensory or motor activity (pacing, licking, swallowing), autonomic patterns (salivation, vomiting, urination), or abnormal behavior (hiding, attention seeking, whining, or agitation) for seconds to minutes before seizure onset
- Ictal period: the seizure itself, when the animal exhibits a variety of signs that may include loss or derangement of consciousness, altered muscle tone or movements, paddling of the limbs, jaw chomping, salivation, and involuntary urination and defecation. This phase usually lasts only seconds to minutes
- Post-ictal period: immediately follows the seizure and reflects transiently abnormal brain function (seconds to several hours), during which time the animal may exhibit abnormal behavior, disorientation, somnolence, or actual neurologic deficits such as blindness, ataxia, weakness, or proprioceptive deficits
Define Epilepsy
Epilepsy is a term used for any condition characterized by chronic recurrent seizures
Seizures can be classified based on their root cause, what are the 3 types of seizures based on cause?
1) Reactive seizures: caused by an extracranial cause e.g. toxins, metabolic diseases
2) Structural Epilepsy: caused by intracranial lesions e.g. congenital malformations, neoplasia, inflammatory disease, vascular disease, storage diseases or degenerative conditions
3) Idiopathic Epilepsy: unknown cause but strong genetic predisposition (GSD, Beagles, Labs, Goldens, Poodles, Border Collies etc.)
Seizures can be classified based on the areas of the brain that are affected, what are the 2 main types of seizures based on location?
1) Focal Seizures: abnormal electrical activity in one area of the brain
2) Generalized Seizures: involve all areas of the brain
How can Idiopathic Epilepsy be diagnosed?
1) Rule out metabolic and structural causes for seizures
2) Genetic basis is strongly suspected: breed and family line are usually affected
3) Usually a generalized tonic-clonic seizure, lasting 1-2 minutes
4) Most common time for IE seizures to occur is during sleep, drifting off to sleep or waking up abruptly. But can be provoked by certain sounds, excitement, hyperventilation or exercise
5) Most show no neurological signs or behavioral changes between seizures (unlike a structural seizure, where there is usually neurological deficits between seizures)
True diagnosis is made by exclusion
What are the most common causes of Structural seizures in young dogs, and in old dogs?
Young dogs: congenital disorders, inherited degenerative conditions and infectious causes of encephalitis
Old dogs: Neoplasia
What are the 4 possible physiological mechanisms of initiation to a seizure?
1) Altered neuronal membrane function
2) Decreased inhibitory neurotransmitters: GABA
3) Increased excitatory neurotransmitters: Glutamate
4) Altered extra-cellular K+ and Ca+ concentrations: during a seizure, extra-cellular K+ increases and Ca2+ decreases, this increases the neuronal excitability and facilitates the initiation and propagation of the electrical potential
How do Anti-epileptic drugs (AEDs) suppress seizures?
By blocking the initiation and/ or propagation of seizures
1) Enhancement of inhibition via the facilitation of the action of GABA
2) Reduction of excitatory transmission
3) Modulation of neuronal membrane conductance
What are the aims of Anti-epileptic drug (AED) therapy?
1) Reduce the seizure severity, incidence and duration
2) Provide minimal side-effects
We are aiming to control, not cure them
What are the common features of the Anti-epileptic drugs (AEDs) ?
- Lipid soluble
- Easily absorbed orally (excluding Phenytoin)
- Peak plasma levels at 4-6 hours
- Volume of distribution more than total body water
- Distribute to the CNS
- Liver-based phase I metabolism
- P450 enzyme inducers
What is the first-line drug used for seizures in dogs and cats?
What is its efficacy and how does it work?
- Phenobarbitone
It is a broad spectrum anticonvulsant - Efficacy: b/w 60-80% of canine patients
- Action: inhibits the release of ACh, Norepinephrine and Glutamate, while potentiates GABA, thus having an overall inhibitory effect on the NS
How long does it take for Phenobarbitone to reach a steady-state?
16 days
What are the side effects associated with Phenobarbitone use?
- Sedation
- PU/PD
- Polyphagia
- Hepatotoxicity
What is Status Epilepticus?
Why is it a medical emergency?
A series of seizures or continuous seizure activity lasting for 5+ minutes without periods of intervening consciousness
Status epilepticus increases blood pressure, body temp, HR, cerebral blood flow and cerebral oxygen consumption, while also decreasing blood pH (due to lactic acidosis), and may decrease effective ventilation
As seizures continue, you will see metabolic deterioration, increased intracranial pressures, acidosis, hyperthermia and cardiac dysrhythmias leading to progressive cerebral ischemia and neuronal death
