CANINE EPILEPSY

What is Canine Epilepsy? 

Canine Epilepsy is a chronic condition characterized by recurrent seizures.  Although seizures are always abnormal events, not all seizures in dogs are caused by canine epilepsy.

Canine Epilepsy is a disorder of the brain where abnormal electrical activity triggers further uncoordinated nerve transmission.  This uncoordinated and haphazard nerve tissue activity scrambles messages to the muscles of your dog's body and the coordinated use of the muscles is then inhibited. 

Because there are many causes of chronic recurrent seizures in dogs, canine epilepsy is not a specific disease or even a single syndrome, but rather a diverse category of disorders.  Canine Epilepsy is broadly divided into idiopathic and symptomatic disorders.  Idiopathic Epilepsy, also called primary epilepsy, means that there is no identifiable brain abnormality other than seizures.  Symptomatic epilepsy (also called secondary epilepsy) is seizures that are the consequence of an identifiable lesion or other specific cause.    

Most dogs with idiopathic epilepsy suffer their first seizure between the ages of one and five years of age.  A genetic basis for idiopathic epilepsy is strongly suspected in several breeds including the Beagle, Belgian Turvuren, Keeshound, Dachshund, British Alsatian, Labrador Retriever, Golden Retriever and Collie.  Idiopathic canine epilepsy may have an inherited basis in other breeds also.

The Seizure 

Watching a beloved dog in the throes of a grand mal seizure is one of the most terrifying scenes you can witness.  A seizure refers to the involuntary contraction of muscles.  The seizure is caused by an electrical storm in the brain.  Seizures can be broken into two types, generalized and partial.  In a generalized seizure, the electrical storm appears everywhere at once.  In a partial seizure, the abnormal electrical impulses begin in a small area of the brain. 

Generalized, tonic-clonic (formerly called grand mal) seizure:  The seizure begins with contraction of all skeletal muscles and loss of consciousness. The dog usually falls to his side with the legs stretched out and the head back.  This is the tonic portion of the seizure.  Sometimes he will vocalize or have facial twitching.  Vocalizations are involuntary and do not indicate pain.  Often the dog will drool excessively, urinate, defecate or eliminate his anal glands.  The tonic portion of the seizure is usually very brief and gives way to the clonic phase of the seizure.  Once the clonic phase begins the dog will have rhythmic movements.  Typically this consists of clamping the jaws and jerking or running movements of the legs.   

Following the seizure, the dog may lay motionless for a brief period.  Eventually he will get up on his feet and may appear to be perfectly normal, but typically will show signs of post ictal behavior.  These signs may include blindness, disorientation, pacing or running about the house bumping into things.  The post-ictal behavior can last anywhere from hours to days after a seizure. 

Not all generalized seizures follow this pattern.  Another type of generalized seizure is the tonic seizure, in which motor activity consists only of generalized muscle rigidity without the clonic phase.  Less common are clonic seizures where there is no tonic phase and some dogs suffer milder generalized tonic-clonic seizures in which consciousness is maintained.

Partial seizures:  Partial seizures are also called focal seizures and as the name indicates, the electrical storm is affecting only a part of the brain.  A partial seizure may stay localized or it may expand to the whole brain and cause a tonic-clonic seizure.  Because the seizure starts in only a part of the brain, an underlying disease or injury is highly suspected.  A partial seizure may remain localized or spread to other parts of the cerebral cortex producing a sequential involvement of other body parts. 

Partial seizures are classified as simple focal seizures when consciousness is preserved and as complex focal seizures when consciousness is altered.  Any portion of the body may be involved during a focal seizure depending on the region of the brain affected.   

In a simple partial seizure, the area of the brain that is affected is the area that controls movement.  Usually the face is affected, resulting in twitching or blinking.  This is usually limited to one side of the face.  If the seizure spreads, other parts of the body on that same side will be affected.  The dog is usually alert and aware of his surroundings. 

A complex partial seizure will originate in the area of the brain that controls behavior and is sometimes called a psychomotor seizure.  During this type of seizure, a dog’s consciousness is altered and he may exhibit bizarre behavior such as unprovoked aggression or extreme irrational fear.  He may run uncontrollably, engage in senseless, repetitive behavior or have fly-snapping episodes where he appears to be biting at imaginary flies around his head.

Cash WC, Blauch BS:  Jaw snapping syndrome in eight dogs.  JAVMS 175:179, 1979
Parent JM Seizures, Small animal medicine 735:741, 1991
Thomas WB: Idiopathic Epilepsy in Dogs. Vet Clinics of N. Amer. Small Animal Practice 183:206, 2000