Most people think of seizures as chaotic brain activity. In fact, seizures are just the opposite. In a normal animal’s electroencephalogram (EEG), it is easy to recognize that there is no distinct pattern to the electrical activity being recorded from the brain.
A seizure occurs when brain cells, which have a natural tendency to “want” to be active, form oscillating or reverberating, synchronous discharges. The summation of several neurons discharging at one time creates an environment where a local abnormality may influence nearby neurons to spontaneously fire, leading to the further discharge of more neurons. As these electrical signals spread throughout the brain, they travel through the normal conductive pathways, eventually reaching areas such as the movement center, resulting in the manifestation of a generalized motor seizure. A seizure is a sudden, involuntary, and synchronous discharge of brain neurons. Seizures are sometimes referred to as convulsions, attacks, fits or an ictus. The condition known as epilepsy specifically refers to recurrent seizures associated with a functional disturbance in the brain.
Whenever your pet is showing signs of a health issue, your first step is to contact your primary care veterinarian. If it is indicated that your pet may suffer from seizures or have another serious condition, a veterinary specialist is available at an ExpertVet certified or affiliated hospital.
Because chronic seizures affect nearly 3% of the canine population, most veterinarians will be presented with numerous cases of dogs with a history of seizures every year. Cats are not nearly affected as often as dogs; however, the same approach to the seizuring patient can be made for cats as well as dogs. The first step in the diagnostic road is to figure out if in fact your pet is having seizures. Other conditions that are commonly mistaken for seizures may include:
- Syncope (not breathing)
- Balance disorders
- Severe muscle weakness
- Neck pain
- Tremor syndromes
- Behavioral abnormalities
It is important to determine if your pet is experiencing a seizure or a “seizure-like” event. There is no etiological significance to a seizure. A seizure simply represents a sign of brain dysfunction. The brain is a fundamentally excitatory organ and it is in your pet’s best interest, for survivability, to be able to take in as much information from its environment as possible. Subsequent to a volley of information, the brain will then discharge its various responses. These responses, by default, will be in an excitatory fashion. This basal excitation can be seen in several areas of the nervous system. For instance, the activation of antigravity muscles when an animal is falling will result in an excitation of extensor muscles on the side the animal is falling to in order to prevent contact with the ground.
The brain is in a constant balance between inhibition and excitation (go or no go). Neurons want to fire and it is up to the inhibitory components of the central nervous system to keep neuronal activation in check. All neurons, if isolated from their surroundings, will fire spontaneously. When the neuron is placed in an environment such as the brain, its firing potential is controlled by other nearby neurons and components of the fluid that surrounds the neurons. The primary means of “quieting” the brain is through inhibitory neurotransmitters (chemicals that allow neurons to "talk" to each other). One of the long-standing hypotheses for the generation of seizure activity is due to a lack of inhibition mechanisms or inhibitory neurotransmitters.
What are the different classifications of seizures?
There are numerous classifications schemes of seizures. In general, seizures can be broken into several categories. Seizures can broadly be divided into three separate classifications:
Primary: Seizures for which no cause can be found. Sometimes referred to as “idiopathic” or “inherited.”
- Typically manifesting in young animals between six months and five years of age, these are seizures for which no cause can be identified. Certain breeds, including (but not limited to) Beagles, Standard Poodles, Labrador Retrievers, German Shepherds, German Pointers, Golden Retrievers, Keeshonds, Irish Wolfhounds, and the Belgian Sheepdog family of breeds, seem to be predisposed to idiopathic epilepsy.
Secondary: Seizures that have a proven cause (see below). Sometimes referred to as “symptomatic.”
- Structural: cancer, intracranial mass, inflammation, infection, stroke, hydrocephalus, trauma, etc.
- Metabolic: liver disease; kidney disease; low blood sugar; toxin ingestion; glucose or electrolyte imbalance, etc.
- Cryptogenic: Seizures suspected to be secondary (structural or metabolic), but no proven cause has been found.
Seizures can then be sub-classified depending upon the type of seizure:
Generalized (previously referred to as “grand mal”)
- Rigidity and contractions
- Rigidity alone
- Contraction alone or alternating relaxation and contraction
- Complete loss of muscle tone
- Brief shock-like contractions of individual muscle groups
Partial or focal
Simple partial: consciousness is maintained
- Rhythmic contractions of facial muscles
- Fly biting
- Lip smacking
- Tail chasing
- Flank sucking
- Obsessive compulsive behavior
- Simple partial: consciousness is maintained
Complex partial: consciousness impaired
- Bizarre behavior
- Abdominal pain