Seizures of unknown cause affect roughly 5% of all dogs. Of those dogs, over half will eventually be diagnosed with canine idiopathic epilepsy. According to Dr. Ned Patterson of the University of Minnesota, 50–60% of dogs who experience their first seizure between the ages of one and five have no identifiable cause for their condition, which is then considered idiopathic epilepsy.
But the prevalence of this seizure disorder in purebred dogs has led researchers to focus on a possible genetic link. And progress is being made in developing tests to identify responsible genes.
What is Canine Idiopathic Epilepsy?
In order to fully understand the complexity of diagnosing idiopathic epilepsy in dogs, it is important to have a clear definition of the disorder. Idiopathic means occurring without known cause and epilepsy is defined as a neurological disorder characterized by unprovoked, recurring seizures that disrupt the nervous system.
A key word here is recurring. A single seizure or even a couple of seizures within a dog’s lifetime are not epilepsy. Idiopathic epilepsy is also known as primary epilepsy and this may actually be a more accurate name for the disorder, as there is increasing evidence for a genetic component to this form of epilepsy in dogs.
The age of onset is also important to consider. Canine idiopathic epilepsy is generally first evidenced between one and five years of age. Dogs may develop seizure disorders later in life, but these are more likely to be linked to age related changes.
Ruling Out Other Causes for Seizures in Dogs
There are many things which can trigger seizures: exposure to chemical or plant toxins, viral diseases such as canine distemper, hypoglycemia, hypocalcemia, hypo– and hyperthyroidism and heart disease, for example, can each cause increased neuronal excitability in the brain. Head trauma can result in brain injury, hydrocephalus (a structural abnormality of the brain), tumors (both cancerous and benign), and liver or kidney dysfunction can cause seizures.
The diagnosis of idiopathic epilepsy is based on ruling out all possible causes for a dog to be experiencing seizures. So if any of these conditions are present, the epilepsy is considered secondary, rather than primary, as there is an underlying cause. And because there is a known cause it cannot be considered idiopathic.
The Role of Genetics in Canine Idiopathic Epilepsy
Increasingly, the role of genetics in idiopathic epilepsy is being explored. Given the numbers of purebred dogs developing primary epilepsy and the apparent familial links in many of those cases, this avenue of research makes sense. And it is beginning to pan out.
The Canine Epilepsy Project is making progress in identifying genetic basis for seizure disorders in dogs. This collaborative effort by the University of Missouri, the University of Minnesota and the Animal Health Trust in the UK, to find the genes responsible will eventually aid dog breeders in their efforts to reduce the prevalence of the disorder in their chosen breeds.
Other scientists are also working on this problem. A German study has provided confirmation of a genetic basis for epilepsy in border collies. Similar work has been done with English springer spaniels, standard poodles, vizslas and Belgian shepherds.
As research progresses and further information becomes available on genetic markers for the disorder, it is likely that this form of seizure disorder in dogs will more rightly be called primary epilepsy as there may be few remaining cases of truly idiopathic canine epilepsy.
The Canine Epilepsy Project. Accessed online June 22, 2011.
More About Epilepsy. Ohio State University Hospital for Companion Animals. Accessed online June 22, 2011
Hülsmeyer, V., Zimmermann, R., Brauer, C., Sauter-Louis, C. and Fischer, A. (2010), Epilepsy in Border Collies: Clinical Manifestation, Outcome, and Mode of Inheritance. Journal of Veterinary Internal Medicine, 24: 171–178. doi:10.1111/j.1939-1676.2009.0438.x