Canine Seizures

Seizures are not common in dogs – but they aren’t rare, either. The Veterinary Information Network estimates that the prevalence in the dog population is about 1%. While distressing to witness, they are rarely life-threatening. After you’ve gotten past the shock of the event and your dog is coming out of the seizure, your mind will be racing. What caused the seizure in the first place? Does your dog have epilepsy? Is this going to happen again? Turns out, these are not always easy questions to answer. 

“Epilepsy” refers to a seizure disorder in which all other possible causes have been eliminated; it is a diagnosis of exclusion. The seizures seem to occur spontaneously, with no underlying structural brain disease or metabolic illness. This means that there is no test that will identify epilepsy. Rather, all other causes must be ruled out before this diagnosis can be made. Doing this can be an extensive and pricey process.

Certain breeds are predisposed to epilepsy, including Beagles, Poodles, Boxers, Labrador Retrievers, Golden Retrievers, Border Collies, and Shelties. While the disease may have genetic roots, it can also occur spontaneously in any dog. 

WHAT IS A SEIZURE?

Seizures occur when neurons in the brain rapidly discharge over and over again. Gamma aminobutyric acid (GABA) is a neurotransmitter in the brain that inhibits excitation of neurons, and in a seizure, the GABA receptor system is particularly involved. When seizures occur, normal GABA inhibition is overcome, and the brain cannot “calm down.” The increased electrical activity leads to changes in behavior, which can manifest in many different ways. 

The classic seizure type, once called grand mal, is now referred to as tonic-clonic; tonic refers to the stiffening of the dog’s muscles and clonic refers to the dog’s twitching or jerking. Strong muscle contractions occur, the dog is unable to stand, and may lose bowel and bladder control. The dog may also vocalize. 

The hallmark of a true seizure is the post-ictal period. Once the muscle contraction ceases and the seizure is over, a dog will take some time (from minutes to hours) to return to normal. In some cases, blindness and disorientation can persist for a day or more. Behavior may be very strange, such as a complete disinterest in food or ravenous eating. Difficulty walking may also occur. Your dog may sleep deeply or be restless. 

Other seizure types include focal seizures (also called petit mal), in which only one part of the body is involved (such as the face); the muscles in that area may twitch or contract. In absence spells, during which a dog is conscious but not responding, the eyes may be open, but he may not answer when his name is called or he is touched. These types of seizures may presage tonic-clonic and can go unnoticed, because they are often subtle. 

In most cases, these electrical discharges are self-limiting, meaning the seizure will cease on its own. In occasional cases, the seizure does not end, leading to a condition called status epilepticus (see sidebar, page 7). 

DIAGNOSTICS

To reach a diagnosis of epilepsy, a thorough work-up will be necessary. At the initial examination, your veterinarian will gather a history. 

Be prepared to answer questions about the duration and severity of any seizures you have witnessed, as well as any precipitating events that you noticed, such as stress, excitement, or sleeping. Toxins or medications in the house are also an important piece of the puzzle. While seizures are distressing to see, getting a video for your veterinarian could help with the diagnosis. Once your dog is in a safe position, try to record the event.

After history-taking, your veterinarian will examine your dog. This nose-to-tail exam will help identify any abnormalities that may point toward a diagnosis. Once completed, the diagnostics start. 

Initially, a “minimum database” of diagnostic tests is recommended. This includes a complete blood count (CBC), chemistry panel, and urinalysis. Depending on your dog’s age, a blood pressure measurement and x-rays may also be recommended. These will identify underlying metabolic causes that can lead to seizures, such as extremely high blood sugar (as in diabetic ketoacidosis) or kidney failure related to antifreeze ingestion. 

CAUSES OF SEIZURES

The cause of seizures can be broken down loosely into age groups:

Puppies younger than 6 months.

It is uncommon for a dog to develop true epilepsy before six months of age. In dogs this young, other causes are much more likely. These can include everything from parasitic infection with protozoa such as Neospora species, to viruses such as canine distemper virus, to toxin exposure (a common problem in curious puppies).

A thorough work-up for a puppy with seizures will include the minimum database above, as well as recommendations for the following (depending on breed and history):

• Bile acid test. This is done if a liver shunt is suspected. Liver shunts are abnormal blood vessels that interfere with proper metabolism by the liver. When present, they can cause seizures and abnormal behavior, especially after meals. Yorkshire Terriers, Maltese, Bichon Frises, and Miniature Poodles are all predisposed. 
• Titers for infectious disease. Canine distemper virus (CDV), the fungi Cryptococcus and Coccidioides, and protozoal diseases such as neospora and toxoplasma can all cause seizure activity.
• Computed Tomography (CT) scan or magnetic resonance imaging (MRI). These tools for imaging the brain can determine whether structural abnormalities like hydrocephalus (a condition where cerebrospinal fluid builds up in a dog’s skull) or Chiari malformation (structural defects in the base of the skull and cerebellum, the part of the brain that controls balance)are present. 
• Cerebrospinal tap. This can help identify meningitis, as seen with inflammation or infection.Work-ups can be expensive and time intensive, so many owners opt to treat with medications and wait to see how the dog responds. With puppies, though, epilepsy is an unlikely cause, which means another disease may be at work and will likely progress and worsen.In puppies, it is also imperative to rule out exposure to toxins. Puppies are naturally inquisitive, and this often leads to accidental exposure to medications, cleaning products, and even illicit drugs. 

Dogs 6 months to 5 years.

At this age, an absence of other clinical symptoms or known toxin exposure makes epilepsy the most common cause. This is especially true in predisposed breeds. As a result, once the minimum database has been completed and obvious causes such as toxins ruled out, many owners opt to treat with anti-seizure medications and see how a patient responds. 

Dogs older than 5 or 6 years.

In dogs older than 5 years, the most common cause of acute onset of seizures is generally a brain lesion, particularly brain tumors (masses). These are usually benign meningiomas, which can cause problems due to pressure on adjacent structures. 

The recommended diagnostics are similar to other age groups, starting with the minimum database. In this group, though, it’s also important to rule out hypertension (by checking blood pressure) and undetected cancer (by taking chest and abdominal x-rays) as possible causes. 

TREATMENT

The treatment for seizures is evolving. First-line therapy remains drug management. These medications are referred to as anti-epileptic drugs (AEDs). Phenobarbital and potassium bromide have long been the drugs of choice, but other medications are now becoming popular. These include Keppra (levetiracetam) and Zonegran (zonisamide). 

Phenobarbital has been used in the management of human seizures for many years. It is reliable, effective, and relatively cheap. However, phenobarbital is a controlled medication and should be handled with care. It must always be stored away from children. 

Phenobarbital works on the dog’s GABA receptors, helping to inhibit the excitation of neurons. 

Phenobarbital does have significant side effects. It can cause ravenous appetite, weight gain, increased drinking and urinating, and induction of liver enzymes. In rare cases, it can cause liver failure. As a result, liver values should be monitored closely (at least every six months) by your veterinarian. If liver enzyme elevations occur, a newer seizure medication may be recommended. 

The dosage of phenobarbital must be individualized, so monitoring the dog’s phenobarbital levels is critical. This is usually initiated about two weeks after starting the medication, when it is expected to reach “steady state” levels. (A drug is at a steady state when the intake of the drug is at an equilibrium with its elimination.) At therapeutic levels, it can cause sedation and ataxia. Usually, dogs will acclimate to this over time. 

About 85 to 90% of dogs will experience a significant reduction in seizure activity with phenobarbital. 

Potassium bromide is also considered a first-line treatment, although this is shifting. Potassium bromide has many of the same side effects of phenobarbital and must also be monitored, as toxicity is possible. It can take up to four months for this medication to reach steady state levels. 

Diet is an important part of therapy with potassium bromide. Food with higher levels of sodium can increase the excretion of potassium bromide, leading to lower levels and increased seizure activity. The dog’s diet must be consistent while on this medication. 

Levetiracetam is being used more frequently to treat seizures. Initially, it was used in humans, and its use has been extrapolated to dogs. Its mechanism of action is not well understood, but it may affect the release of neurotransmitters. It is minimally metabolized by the liver, so it doesn’t cause the liver enzyme elevations that are seen with phenobarbital. Levetiracetam levels in the blood are therapeutic within about 24 to 36 hours (versus two weeks for phenobarbital). 

Levetiracetam also does not cause ravenous appetite and weight gain. It is considered so safe that regular monitoring is not usually necessary. It is important to note that two formulations are available and each must be given in different ways. “Regular” Keppra must be given every eight hours; Keppra-XR, an extended release formulation, can be given every 12 hours but cannot be crushed and placed in food (doing so would thwart the mechanisms that cause the drug to be released continuously over a 12-hour period). 

Zonisamide does not act as quickly as Keppra but is faster than phenobarbital (about one week to reach steady state). Like Keppra, zonisamide generally has minimal effects on the liver. It does, however, have some rare side effects such as hepatopathy (liver congestion), dry eye, bladder stones, and hypothyroidism. Regular bloodwork monitoring is generally not necessary, but any changes in a dog’s condition should always be brought to the attention of your veterinarian. 

Unfortunately, medications are often a life-long necessity. Working closely with your veterinarian to taper to the lowest dose possible for management is the best approach. 

ALTERNATIVE THERAPIES

Products containing CBD (cannabidiol, a phytochemical compound extracted from cannabis plants) are becoming popular with owners as an adjunctive therapy for many illnesses. It is important to know that currently, other than in a handful of states, veterinarians are not allowed to recommend or discuss CBD as a treatment (see “Know Your CBDs,” WDJ August 2019).

A study published in the Journal of the American Veterinary Medical Association (“Randomized blinded controlled clinical trial to assess the effect of oral cannabidiol administration in addition to conventional anti-epileptic treatment on seizure frequency in dogs with intractable idiopathic epilepsy,” June 1, 2019) evaluated CBD as an additional treatment in patients with intractable seizures. 

While the use of CBD was associated with a significant decrease in seizure activity, further investigation is warranted before therapeutic recommendations can be made. As laws change, your veterinarian may be able to discuss this with you. Use caution when choosing to administer CBD products without veterinary supervision, as neither the side effects nor interactions with other, FDA-approved medications are well understood. 

In 2015, a study supported the use of medium chain triglycerides (MCT) as a dietary supplement to decrease seizures. The diet studied was ketogenic (high fat, low proteins and carbohydrates). There are a few commercial diets available that address this need and may be helpful in managing seizures. 

Nutritional supplements such as omega-3 fatty acids, thiamine (vitamin B1), vitamin E, and s-adenosyl methionine with milk thistle may also have some benefit when used in conjunction with standard Debra Canapp treatment. Much of the knowledge we have in veterinary medicine about these supplements is extrapolated from human medical studies and anecdotal. However, the supplements are unlikely to cause harm. As always, consult with your veterinarian before adding any supplements to current treatments. 

Lastly, several studies have demonstrated possible benefit with the use of acupuncture. The exact reason acupuncture may help lower seizure frequency is not understood. The theory is that acupuncture stimulates the release of inhibitory neurotransmitters, therefore “calming” the brain. While it is not typically first-line treatment, in patients with intractable seizures or those with poor response to medications, it is another modality that may offer some relief. 

After nine years in emergency medicine, Catherine Ashe, DVM, now works as a relief veterinarian in Asheville, NC, and loves the GP side of medicine.