Seizures and status epilepticus (Proceedings) - Veterinary Healthcare
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Seizures and status epilepticus (Proceedings)


CVC IN KANSAS CITY PROCEEDINGS


Definitions

    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.

Classification

          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.
    3. 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.
      • Excess 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.
      • Insufficient inhibition
          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.

Seizure stages

      • 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

    1. Generalized seizures – involves both sides of the forebrain simultaneously
      • Loss of consciousness, laterally recumbent
      • Tonic-clonic activity
      • 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
          b. 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


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Source: CVC IN KANSAS CITY PROCEEDINGS,
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