Causes of Canine Seizures

Watching your dog have a seizure can be a frightening experience. Time stands still in that moment and you feel helpless – but there is something you can do. Seizures in dogs can have many different causes or triggers, so having your dog evaluated by his veterinarian can help find the problem and thus, appropriate treatments available for this condition. Even “idiopathic” seizures – ones whose cause can’t be determined – can be treated.

What is a seizure?

A seizure is a period of abnormal electrical activity in the brain. This activity between brain cells can cause loss of consciousness, paddling of the limbs, and involuntary urination and defecation.

If the abnormal electrical activity is limited to only one small part of the brain, signs of a “focal seizure” may be observed; these include staring off into space and not responding to external stimuli, an involuntary jaw movement that looks like a dog is chewing gum, and/or tremors.

Seizures can last a few seconds up to several minutes or more. Any seizure lasting more than five minutes requires immediate veterinary intervention to stop the seizure.

What causes seizures?

Causes of seizures in dogs can be broadly classified into two categories: intracranial (problem inside the brain) and extracranial (problem outside the brain). The list of extracranial causes is much longer and more extensive than the list of intracranial causes.

• Intracranial causes of seizures

Intracranial causes of seizures can be thought of as structural problems of the brain. This means that the brain is temporarily or permanently altered in some way. Causes include:

• Infection of the brain or meninges (linings around the brain). This includes canine distemper virus, rabies, the fungus Cryptococcus, and the protozoal parasites Neospora caninum and Toxoplasma gondii. Canine distemper tends to affect young puppies but can also affect adult dogs who have not been vaccinated for this virus. The other organisms can affect dogs and puppies of any age.
• Congenital abnormalities such as hydrocephalus. This abnormality is something that a dog is born with, so seizures in these cases typically start in young puppies.
• Brain tumors, either a single tumor that originates in the brain or multiple tumors that have spread from another location in the body. Brain tumors can be seen at any age but are more likely to be seen in older dogs.
• Recent head trauma, such as a skull fracture or concussion.
• Degeneration of brain cells caused by exposure to a neurotoxin, such as lead, mercury, toxins produced by blue-green algae, and many others.
• Extracranial causes of seizures

The brain is a very sensitive organ that requires a tightly controlled environment. When there is a problem in the body that alters the brain’s environment, the otherwise normal brain becomes reactive to the change. This reaction often manifests as a seizure. Causes include:

• • Hypoglycemia (low blood sugar). This is one of the first things your veterinarian will check for if your dog is actively having a seizure. There are many causes of hypoglycemia, including liver disease, pancreatic tumors, insulin overdose in diabetic dogs, and ingestion of a product containing xylitol. It can also be seen in young puppies that are not eating well, particularly small and toy breed puppies.
  • Hyperkalemia (high potassium). The most common causes of hyperkalemia in dogs are kidney failure, stones in the urinary system that obstruct a dog’s ability to urinate, and hypoadrenocorticism (Addison’s disease).

• Hypocalcemia (low calcium). This can be seen in kidney failure, eclampsia in female dogs that are nursing puppies, and dogs with pancreatitis.
• Hypoxemia (low oxygen concentration in blood). This can be caused by any condition that impairs a dog’s ability to breathe or to circulate blood effectively, such as pneumonia or a heart condition.
• Liver shunt (also known as a portosystemic shunt). A liver shunt is an abnormal blood vessel that allows blood returning from the gastrointestinal system to bypass the liver. Since the liver is responsible for metabolizing proteins that are absorbed by the small intestine, this means that some of these proteins are able to reach the brain before they are processed. Most shunts are congenital, but liver failure can cause the formation of shunts.
• A high body temperature can be caused by infection, heat stroke, and prolonged seizure activity. Experiencing a seizure that lasts longer than five minutes can increase body temperature and cause more seizures, regardless of the original cause for the seizure activity.

Seizures with an extracranial cause typically resolve once the underlying problem is found and treated.

Idiopathic epilepsy

Idiopathic epilepsy affects young dogs between the ages of 6 months and 6 years. The cause of idiopathic epilepsy is unknown. It is a diagnosis of exclusion, meaning that other causes of seizures must be ruled out before making this diagnosis.

Any breed of dog can be affected by idiopathic epilepsy. However, it is diagnosed more often in Collies, Bassett Hounds, Cocker Spaniels, Labrador Retrievers, and Golden Retrievers.

identifying the cause

If your dog is experiencing seizures, have your dog assessed by a veterinarian as soon as possible. Your veterinarian will want complete bloodwork, a urinalysis, and x-rays of the chest and abdomen. She may also want to check your dog’s blood pressure and order additional tests based on what she finds on the initial diagnostics. Your dog may be referred to a veterinary neurologist for an MRI of his brain if an extracranial cause of his seizures can not be found.

There are many causes of seizures in dogs. But seizures can be effectively managed or resolved in most cases when the underlying cause is properly diagnosed.