Ask a Vet: What Causes Seizures in Older Dogs?

For years, conventional wisdom held that most seizures in older dogs were caused by brain tumors, but a new study challenges that.

Dr. Eric Barchas  |  Mar 10th 2015


I will never forget the first time I witnessed a seizure. I was about 12 years old, and I was in my childhood kitchen with my mother and my cat (yes, this article is about dogs, but bear with me). The cat walked into the middle of the room, and then adopted a distant, disoriented gaze. She defecated, and then she collapsed into convulsions. It was the most frightening thing I had witnessed up to that point in my short life — I was convinced she was going to die right then and there. Imagine my surprise when, 10 minutes later, she was back to normal and acting like nothing had happened.

When we described the episode to our veterinarian, he was at a loss for an explanation. My cat suffered from two or three similar episodes during her long life, and she ultimately died of unrelated causes. It was not until 15 years later, when I was in the process of my veterinary neurology studies, that I understood what had occurred. My cat had epilepsy.

Epilepsy is a disorder that leads to seizures. And it doesn’t just happen in cats and people. Dogs are prone to it as well.

Epilepsy is a syndrome — or much more likely a group of syndromes — characterized by excess electrical activity in the brain. Typically, dogs will have one or more areas, called foci, of excess activity. The brain is composed of cells that communicate through electrical impulses. When electrical activity spreads out of a focal area, it can unleash a chain reaction. Each new area stimulates nearby areas, which in turn stimulate more areas until the entire brain is overcome with a firestorm of electrical activity. This firestorm causes the classic, dramatic, frightening convulsions called grand mal seizures.

Not all seizures are as dramatic as the one I witnessed as a 12-year-old. So-called petit mal seizures in dogs may cause localized muscle fasciculations or tremors, or periods of disorientation or head bobbing, or even activities that appear to resemble snapping at flies.

There are many different causes for seizures. Epilepsy has been mentioned, and it is known to be the most common cause of seizures in young dogs. Epilepsy has a hereditary component, and some breeds (such as most types of Bulldogs) appear to suffer from epilepsy at higher rates than others.

Other causes of seizures include head trauma, congenital brain anomalies, exposure to toxins (such as snail bait or cheap flea preventatives), encephalitis (infection or inflammation of the brain), meningitis, congenital irregularities with the liver, and some metabolic problems such as liver failure or kidney failure.

And then there are brain tumors. Brain tumors absolutely can cause seizures.

Now here’s the really scary thing: For many years, conventional wisdom in the veterinary world has held that most dogs who have a first seizure at a young age (less than five years) will be diagnosed with epilepsy. Epilepsy is not a good thing, but in most cases it is controllable with medications, and in some cases owners of dogs with epilepsy opt not to medicate and their dogs still generally do well. And epilepsy doesn’t carry the emotional fear factor of the “big C” — cancer.

The flip side of that conventional wisdom was this: A majority of dogs who suffer first seizures at a more advanced age — greater than seven years — would ultimately be diagnosed with intracranial disease. Intracranial disease is a group of problems that includes encephalitis and meningitis, but in reality when vets refer to intracranial disease they usually mean brain tumors.

In other words, conventional wisdom held that brain tumors were responsible in most cases in which dogs greater than seven years of age suffered from first seizures. Dogs aged five to seven were left in a grey area that was more-or-less devoid of conventional wisdom.

I have always believed in honesty when discussing these matters with clients. Over the years I have caused many a tear to fall when I mentioned the above information about brain tumors to owners who were already suffering from the stress of having seen their dog go through a seizure.

Therefore, I always have been quick to follow with a personal observation, and that is this: My personal experience has been very different from the conventional wisdom. I have treated many hundreds of older dogs for seizures, and many of them did not turn out to have brain tumors.

Now, happily, I can rely on more than my own personal experience to console pet owners in such circumstances. The February 15, 2015 Journal of the American Veterinary Medical Association (JAVMA) contained a paper entitled, “Epilepsy in dogs five years of age and older: 99 cases (2006-20011).” The authors of the study found that of the dogs diagnosed with epilepsy, primary epilepsy (the type we have been discussing here) was diagnosed in 23 percent of the dogs aged five to seven years, 45 percent of the dogs aged eight to 10 years, 39 percent of the dogs aged 11 to 13 years, and 29 percent of the dogs older than 14 (although a small sample size might make it hard to extrapolate much among the oldest dogs).

And what about brain tumors? They were found in 40 percent of dogs in the five-to-seven-year group (encephalitis and other causes made up the remaining 37 percent), and in 48 percent of the dogs in the 11-to-13-year group (leaving encephalitis and other causes with 13 percent). Sadly, brain tumors were found in all of the non-epileptic members of the two remaining groups (55 percent of dogs aged eight to 10 years and 71 percent of dogs older than 14).

What does this mean? Sadly, brain tumors are still common causes of seizures in older dogs. However, the conventional wisdom had held that a vast majority of older dogs with seizures had brain tumors. It now looks like the number is closer to 50 percent, at least for dogs under 14.

Fifty percent odds are not good, but they are much better than what had previously been thought by most vets. It’s not perfect, but it’s an improvement, and I’ll take it.

Learn more about dog health from Dr. Eric Barchas:

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