1. Seizure- transient self-limiting clinical manifestation of excessive hypersynchronous electrical activity in the CNS. Always indicates electrical dysfunction in the forebrain.
2. Epilepsy- a chronic neurological condition characterized by recurrent seizures.
a. Reactive: Secondary to a metabolic or toxic condition
b. Symptomatic: Secondary to structural brain disease
c. Idiopathic: No identifiable cause
d. Cryptogenic: Epilepsy is thought to be symptomatic, but the etiology has not been determined.
Cluster seizures- Two or more seizures within a 24 hour period
4. Status Epilepticus- A neurological emergency, but no universally accepted definition. Practically- continuous seizure activity, or two or more seizures between which there is incomplete recovery of consciousness, lasting at least 5 minutes.
Pathophysiology of seizures
The pathophysiological mechanisms that cause seizures are poorly understood. Neurons are excitable tissue constantly held in check. Neurons have a seizure threshold and seizures result when the threshold is lowered and there is imbalance between excitatory and inhibitory mechanisms that favors excitation.
o Glutamate is the major excitatory neurotransmitter in the CNS, others include aspartate and acetylcholine. Glutamate can bind to NMDA or non-NMDA receptors resulting in sodium influx into a neuronal cell and neuronal excitation.
o Gamma-aminobutryic acid (GABA) is the main inhibitory neurotransmitter in the CNS; others include glycine, taurine and norepinephrine. GABA binds to its receptor which leads to opening of a chloride channel leading to hyperpolarization and inhibition.
• Aura: initiation of abnormal electrical activity; occurs minutes prior to ictus; animal may hide, whine, appear anxious, salivate, or seek out owner.
• Ictus: The actual seizure
• Postictal phase: behavior changes, ataxia, lethargy, blindness or disorientation; may last minutes to a day or more
Types of seizures
Generalized seizures – involves both sides of the forebrain simultaneously
Loss of consciousness, laterally recumbent
• Autonomic signs: salivation, urination, defecation
2. Partial seizures – abnormal neuronal activity in one region of forebrain. Partial (focal) seizures may or may not progress to generalized seizures.
a. Simple partial seizure: abnormal motor neuron discharge originating in contralateral cerebral hemisphere
Consciousness usually not impaired
Facial twitching and limb movement are common
Complex partial seizure (psychomotor seizure) – behavioral abnormalities thought to originate from the limbic system or temporal lobe
Consciousness is usually impaired
Flybiting and tail chasing are common manifestations in dogs
Features in cats are more variable and might include drooling, growling, or skittish behavior