What causes epilepsy in dogs?

Epileptic seizures are a result of abnormal and excessive electrical activity in the brain. Canine epilepsy can manifest itself in many ways, depending on the location and strength of the abnormal electrical signals in the brain.

There are three main reasons why this abnormal electrical activity can occur; reactive seizures, structural or idiopathic epilepsy.



Reactive Seizures

Reactive seizures are where a normal brain reacts to something external, such as:

  • poisoning – ingestion of a toxin such as chocolate or ibuprofen that can trigger seizures (a convulsant)
  • a metabolic disorder – a problem in an organ other than the brain, such as liver dysfunction, hypoglycaemia (low blood sugar) etc.

Structural epilepsy

In these cases, epilepsy is secondary to damage in the brain itself, and can affect dogs at any age, young or old. The damage in the brain can take many forms, such as a congenital abnormalities, inflammation (meningitis/meningoencephalitis) or a mass (abscess, tumour). Depending on the severity and location of the damage, there may be other signs as well as the seizures, such as circling in the same direction, blindness on one side, disorientation, and pressing their head against a wall.


Idiopathic epilepsy

Idiopathic epilepsy is the most common form of epilepsy in dogs.

It is a diagnosis of exclusion, meaning that the other causes of seizures should have been ruled out before coming to the conclusion of idiopathic epilepsy. It usually first develops in animals aged between 6 months and 6 years. As a general rule, the dog will be themselves and act normally between seizures.

Idiopathic epilepsy may be genetic in origin and many breeds are predisposed (see What breeds are affected by epilepsy?).


A genetic cause of idiopathic epilepsy

It is estimated that canine epilepsy affects up to 1 in every 17 dogs around the world (all breeds combined).
However, it is much more common in certain breeds, with a prevalence of up to 20%, or 1 in every 5 dogs. This is because some dogs can have a genetic predisposition to idiopathic epilepsy.

There is no single type of genetic epilepsy in dogs, and there are as many forms as there are breeds affected. The characteristics (clinical signs or seizure type, age of onset of seizures, gender predisposition, treatment response, prognosis) are usually similar within a given breed, but vary from one breed to the next. This suggests that the gene or genes responsible for the condition differ between these breeds.