by Karen Leshkivich, DVM

Epilepsy is divided into three types: Primary epileptic seizures (PES--i.e.idiopathic, inherited), Secondary epileptic seizures (SES), and Reactive epileptic seizures (RES).

Primary epileptic seizures are defined as abnormal brain function without any structural abnormalities in the brain.  The seizure is the result of abnormal neurological imbalance in the brain.  PES is what most breeders are concerned with since there is a genetic tendency with this form of epilepsy.  But PES is not the only cause of seizures in dogs.  PES is a 'diagnosis of exclusion,' in other words all other causes of seizures are ruled out before the diagnosis of 'Epilepsy' is made.  There are at least 50 categories of problems that can cause seizures that are not the inherited 'epilepsy' that people first think of with the mention of the word 'seizure' (these are listed at the end of this article).  It is documented that 1% to 6% of purebred dogs are affected with the hereditary (idiopathic) epilepsy.  This is a single gene disorder that is recessive.  Since it is a single gene defect in one gene (the actual gene affected is probably different for each breed of dog), in order for a dog to show signs of hereditary epilepsy, siblings, half siblings, a parent and at least one offspring must have the defective gene.  In general, it is recommended that any dog with epilepsy not be bred, as well as any siblings or parents.

Secondary epilepsy seizures (SES) are defined as abnormal brain function associated with changes in the brain.  There are so  many causes of SES that I will list them at the end of the article to save time, but they include developmental, inflammatory, infectious, vascular, neoplasia (cancer), trauma and toxins.  One of my own bloodhounds had begun having seizures at the age of 5, a few months after having had a litter.  Initially, she only had short episodes of being non-responsive and weak that occurred sporadically.  At that time, tests indicated that she had a white blood cell count of 50,000 (normal is 10,000).  We treated her with antibiotics, and the 'episodes' stopped.  About 6 months later, she began having frequent episodes of collapse, focal seizures and non-responsiveness, which escalated to full-blown seizures.  Multiple tests were run on her, and even though she was always current on vaccinations, part of the neurological screening included a Distemper titer and conjuctival swab to look for Distemper bodies.  The Distemper tests came back postive--she had active Canine Distemper even though she was fully vaccinated and an adult.  To end the story, she was one of the very few that survived Distemper and her seizures stopped completely.  She lived to be the age of 11 with no further health problems.  None of her offspring ever exhibited any seizures.  What had apparently happened with her was that the fulminate infection she had after having her litter (a severe uterine infection--endometritis), had compromised her immune system to the point that she did not respond to her yearly vaccination boosters; she had contacted a dog infected with Distemper and had contracted the disease.  Her initial bouts of 'seizures' were due to the bacterial infection and the more severe seizures that occurred later were due to the viral Distemper infection in her brain.  I told this story about one of my dogs, although it was a difficult time for both me and her, to show that seizures can be caused by, many other things other than hereditary epilepsy.

Reactive epileptic seizures (RES) are a reaction of the brain to systemic insult or physiologic stress (something else wrong in the body).  Again, the list of causes is quite long and is summarized at the end of this article, but the major categories include: organ failure, electrolyte imbalance and energy deprivation.  Simple things like low blood sugar can cause seizures; heart disease, liver disease, toxins that upset the sodium balance in the body--can all result in a reactive epileptic seizure.

Although the causes of epileptic seizures are many, they all can result in similar appearing seizures.  Not to diminish the importance of being aware of the presence of hereditary seizures, it is important to determine the cause of the seizure so that an underlying condition can be treated.  Only after all other causes have been ruled out can one say that a seizure was a result of hereditary epilepsy.

Causes of Seizures

                                  Form                                                          Cause

 Primary Epileptic Seizures (PES) Hereditary
Secondary Epileptic Seizures SES) Developmental/Congenital:
porencephaly (cysts in brain)
cortical dysplasia
vascular malformation 
Canine distemper
  Immune mediated:
Granulomatous Meningioencephalitis 
Cortocosteroid responsive inflammatory conditions
Thromboembolic: septic, tumor, cardiac spasm
  Neoplasia (tumor, cancer)
ethylene glycol
Reactive Epileptic Seizures (RES) Organ failure: 
hepatic encephalopathy (liver disease)
portosystemic shunt
uremic execephalopathy (kidney failure)
chronic kidney failure
  Electrolyte imbalance:
sodium decrease
sodium increase
calcium decrease: pancreatitis, kidney disease 
  Energy deprivation:
Thiamine deficiency 
  Hypoxia (decreased oxygen):
shock, heart failure
  Ischemia(decreased blood pressure): 
shock, heart failure 
juvenile hypoglycemia
hunting dog hypoglycemia
endocrine disease