What causes seizures?

Normal neurons (brain cells) use electrical and chemical signals to communicate with each other.  This communication can either be excitatory which activates the next neuron, or inhibitory which shuts off the next neuron.  The mechanism causing seizures in primary epilepsy is thought to be an imbalance in the excitatory and inhibitory signals to the brain.   Every dog (and person) has a seizure threshold of neurological activity.   Normally the excitatory and inhibitory signals are in balance which keeps the electrical activity below the seizure threshold.  If the balance within the neurons shifts too far towards excitation, too many cells may become excited and a seizure will result.  This excitation happens within the brain and is not related to your dog becoming excited about his favorite activity.  In fact most seizures occur while a dog is at rest or asleep.

It is often difficult to determine what type of seizure your dog is having, therefore, it is very important that you keep calm when your dog has a seizure and observe him or her very closely.  Since seizures rarely happen at your vets office, a detailed written description or a video of the seizure may help in the treatment and diagnosis of epilepsy.

The following is a list of seizure types in humans as defined by the International Classification of Epileptic Seizures (ICES).   

International Classification of Epileptic Seizures:

Simple partial seizures

All partial seizures are characterized by onset in a limited area, or focus of one cerebral hemisphere.  The ICES classifies simple partial seizures as those that are not associated with any impairment of consciousness.    Although the ability to respond may be preserved, motor manifestations or anxiety relating to the seizure's symptoms may prevent your pup from responding appropriately.

Motor simple partial seizures alter muscle activity.  Frequently motor seizures Partial seizures with motor symptoms will cause stiffening or jerking of the legs on one side of the body.  Another common simple partial seizure is facial twitching usually on one side of the head.  Any muscle group may be involved.  Abnormal movements may be restricted to one body part or gradually spread to adjacent areas on the same side of the body or both sides of the body with loss of consciousness (secondary generalized seizure).

Sensory seizures  cause hallucinations or illusions (distortion of a true sensation).  Hallucinations may remain restricted to one area or spread to other areas.  Hallucinations can involve any sensory modality, including touch (pins and needles) smell or taste, vision and hearing (buzzing).  Unfortunately our dogs can't tell us what happened, even when consciousness is preserved during a seizure, so we don't know for sure if our pups have sensory seizures. 

Autonomic seizures cause vomiting, pain, hunger, warmth, and heart palpitations.

Psychic seizures affect how dogs  feel, think and experience things.   Psychic seizures can evoke spontaneous emotions like extreme fear or aggression.   A seizure should be suspected for any dog who exhibits brief periods of  unprovoked, extreme fear or aggression.

Complex partial seizures

Complex partial seizures cause impaired consciousness and arise from a single region in the brain.  Impaired consciousness implies decreased responsiveness and awareness of self and surroundings, however consciousness many not be impaired completely.  In people, there is often no memory of what happened during all or part of the complex partial seizure.  Automatisms (automatic repetitive movements) are common and may involve any body part.  The mouth is frequently involved and automations may include lip smacking, chewing or swallowing.  The limbs may also be involved with either simple movements involving one leg, or with very complex coordinated movements involving bilateral limbs.  Some examples of complex movements are cycling or swimming motions.

Generalized Seizures

Seizures are classified as generalized seizures when the first clinical signs indicate that both sides of the brain are involved in the seizure.  Consciousness may, or may not be impaired.  Muscle involvement happens on both sides of the body.  The following are some types of generalized seizures:

Absence seizures (Petit Mal) are common in humans and are described as an abrupt and brief loss of consciousness.  True absence seizures are rare or at least rarely recognized in veterinary medicine.

Myoclonic seizures are characterized by a brief, shock-like jerking of a muscle or group of muscles.

Clonic seizures are seizures that involve rhythmic contractions of muscles.  Typically a dog will paddle or have jerking motion in the limbs and chewing movements.

Tonic seizures causes generalized muscle rigidity.  In dogs, the limbs are usually extended and stiff and the mouth may appear to be locked in an open position.  Some dogs do not breath during a tonic seizure or during the tonic phase of a tonic clonic seizure.

Tonic-clonic seizures were formerly called grand mal seizures and are the most common type of  generalized  seizure in dogs.  Typically a dog will loose consciousness, fall to his/her side with limbs extended and rigid.  The mouth may appear to be locked in an open position and the neck may be extended extremely far back.  All muscles in the body are contracted.  The result of the muscles in the lungs contracting forces air out which sometimes appears like crying out.   Breathing may stop for a short time and cyanosis (turning blue) may occur.  A dog may also urinate, defecate or express his anal glands during this phase of the seizure.  The tonic phase gives way to the clonic phase of the seizure and paddling or jerking of the limbs and chewing movements begin.  After a minute or so, the muscles relax and the dog's body goes limp.  At this point the dog is deeply unconscious.  Slowly they will regain consciousness, but they may remain groggy and confused for several minutes after the seizure.  

Some dogs have milder tonic-clonic seizures where consciousness is maintained and muscle movement is not as violent.

Atonic seizures are, in a way, the opposite of tonic seizures.  Instead of the body going stiff, all muscle tone is lost.  These seizures are sometimes called "drop attacks" because when a dog looses all muscle tone he drops to the ground.

As you can see from the descriptions, seizures are very complex.  They may start out as one type and progress to another.  Knowing what type of seizure your dog is having is not as important as knowing when your dog is in trouble.  Please be sure to ask your vet when you need to seek emergency treatment. 

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