Primary Epilepsy in the Toy Dog

Primary Epilepsy in the Toy Dog

by Leanne Bertani

definition

Primary Epilepsy is a disorder of the brain characterized by recurrent seizures. The exact cause is unknown, but is probably some kind of biochemical or electrical discharge in the brain. It usually presents itself between the age of six months and five years, most commonly prior to the age of three.

incidence

Epilepsy is a relatively common condition in all dogs, probably occurring in between 1% and 4% of them. A higher incidence has been reported in the beagle, Belgian Tervuren, border collie, boxer, cocker spaniel, collie, dachshund, German shepherd, golden retriever, poodle, Saint Bernard, shetland, Siberian husky, springer spaniel, Welsh corgi, and wirehaired fox terrier. It is not common in dobermans or sight hounds. Most seizures occur when the animal is at rest, so many of them happen early in the morning or late in the evening. For this reason, the incidence of seizures may be underestimated in dogs residing in kennels. Some owners have also reported an increase in seizure activity if the dog is very excited. Partial seizure disorders may be more common than generalized seizure disorders.

types of seizures and their symptoms

The current categorization of seizures divides them into (a) generalized, and (b) partial. A generalized seizure involves the entire brain; a partial seizure only involves part of the brain.

Generalized seizures (used to be called “Grand Mal”) are bilateral and symmetrical (involve both sides of the body) and include loss of consciousness. During a generalized seizure, the dog will usually become stiff, chomp its jaw, and salivate profusely. The seizure may be accompanied by urinating, defecating, making noise or paddling of the feet.

A partial seizure (previously known as Petit Mal) is generally milder. The symptoms can be so subtle that the seizure goes unrecognized. Symptoms can include a “wide-eyed look” or vacant stare, drooling, staggering, trembling, movement of one limb, or even biting at imaginary flies.

Some dogs recover immediately; others may have several hours of confusion, sleepiness, or restlessness after a seizure.

stages of a seizure

prodrome and aura – occasional changes in behavior prior to a seizure, such as restlessness, whining, salivating or just wanting to be held.

ictus – actual physical activity of the seizure, usually causing increased muscle tone or movement, commonly lasting 1-3 minutes

postictus – usually lasts less than 24 hours; may include pacing, eating and drinking voraciously, acting deaf or blind, or just being more quiet than usual.

what to do when your dog has a seizure

The dog probably has no memory of the event, so the seizure is likely to be more terrifying to watch than it is to experience. The best thing you can do for your dog is to remain calm and in control, so that when he comes out of the seizure, he won’t sense your anxiety.

As long as the seizure lasts less than five minutes, you don’t really have to do anything but keep your dog from flailing into hard objects. If the dog is at risk of injury, move him to a safe place, such as on a rug or blanket, and protect him from other dogs if necessary.

Some owners prefer to hold their dogs during the seizure, but be aware that the need for oxygen may be greater during a seizure so it is important not to constrict the chest or obstruct air flow. Do not attempt to restrict movement of the extremities, and do not put your hands into the dog’s mouth. A towel on the lap may help protect from any spontaneous excrement.

After the seizure is over, take your cue from the dog. If he prefers to be alone, let him rest in a crate or in a corner. If he wants to be with you, keep him in a calm environment. Any panic or excitement in your voice may increase the dog’s confusion. Record the date and duration of the seizure on a calendar, so that you can share that information with your veterinarian.

If you suspect that the seizure may be due to hypoglycemia, (for instance, in a young puppy or a thin dog that hasn’t been eating well) try administering a small amount of sugar (in the form of Nutrical, frosting, syrup, etc) into the pouch of the mouth when it is over, followed by a protein snack such as cheese or a dog biscuit when he is able to eat.

While simple carbohydrates are preferred to treat hypoglycemia, I don’t agree with the practice of routine administration of simple carbohydrates to prevent hypoglycemia. This practice causes wild fluctuations in blood sugar and insulin production, and may cause a rebound hypoglycemia. A hypoglycemia-prone dog would be much better served by more frequent feeding of protein and complex carbohydrate meals.

at the vet’s office

A single seizure is generally not an emergency. The only time you need to rush to the vet is when a seizure lasts for more than five minutes, or if it occurs in a lactating female, or a very young puppy in which an infection such as distemper is suspected. Multiple seizures in the same day also require an emergent veterinary visit. Otherwise, visit the veterinarian at the earliest convenience.

If there has only been one seizure and the dog is in the normal age range for the onset of epilepsy, then nothing more than an exam may be done at the initial veterinary visit. If the dog is out of the usual age range, or there are abnormalities on physical exam, the veterinarian may begin to look for other causes of seizures. Possible tests that could be done include thyroid function tests, glucose tolerance tests, electroencephalograms, blood test for lead poisoning, spinal taps to look for distemper or other infectious disease, or CT scan or MRI.

The diagnosis of Primary Epilepsy is established by ruling out other causes of seizures. If the first seizure occurs between the ages of one and three years of age, Primary Epilepsy is the most likely cause. Other (secondary) causes are hypoglycemia, hydrocephalus and liver shunt (especially in a puppy), or brain tumor and cardiac arrhythmia (particularly in the elderly dog). Less common causes include metabolic disorders such as hypothyroidism, toxins, infections, autoimmune problems, heat stroke, head trauma, parasites, vitamin deficiency, low serum calcium, liver or kidney failure or other causes of blood chemistry abnormalities.

cluster seizures and status epilepticus

Although the majority of seizures due to Primary Epilepsy aren’t life-threatening, there are a couple conditions that require aggressive medical attention. The first is “cluster seizures”, a condition where the seizures occur at regular intervals of 1-4 weeks. This condition is more common in larger breed dogs, and Valium is a common treatment.

The second, and more critical, emergency is “status epilepticus”, a continuous seizure lasting more than five minutes, or two or more seizures with incomplete recovery time between them. This condition usually responds to oxygen and intravenous valium, but can occasionally result in death.

breeding advice

Primary Epilepsy has been shown to be inherited in some breeds. The mode of inheritance is probably not the same in all breeds. Studies done in the late 90’s suggest that it may be autosomal recessive in Keeshonds, polygenic with one gene of major influence in Belgian Tervurens, and polygenic recessive in Golden Retrievers. It is thought by some that generalized seizures are more likely to have a genetic origin than partial seizures.

It is probably unwise to repeat a breeding that has resulted in a dog with Primary Epilepsy, and certainly unwise to use an epileptic animal in a breeding program unless one is prepared for the consequences. Test breedings of epileptic sires and dams have produced incidences of epilepsy from between 38 percent (outcrosses) to 100% (mating of two epileptic siblings).

Delaying the first breeding of related dogs until after the age of three may allow time for a larger percentage of epileptic dogs to be diagnosed.

If epilepsy is a major problem in a breeding program, then experts suggest refraining from using siblings of epileptic animals. If you must breed a sibling, do not breed that sibling to any first-degree relative of an epileptic dog or to a dog that has produced an epileptic dog. In the words of Jerold S. Bell, D.V.M. and Clinical Assistant Professor of Genetics, Tufts University School of Veterinary Medicine, “Find a low risk mate, breed, and replace her in the breeding program (not in your heart or home) with a quality offspring.”

treatment

If a specific cause for a seizure is found on examination, then the seizure is not due to Primary Epilepsy, but is considered to be “secondary”, and the treatment is directed to the cause. If no cause is found, the first seizure is not usually treated. In general, most veterinarians will not medicate for Primary Epilepsy unless there is more than one seizure every 4-8 weeks, or unless the dog has cluster seizures or status epilepticus.

There is some evidence that seizure frequency continues to increase if left untreated (ie. that the brain “learns” to seizure, or that seizures have a “kindling” effect), so most dogs that have an epileptic seizure more than every 4 weeks or so should be put on medication. Phenobarbital is the most commonly used medicine. It is usually given in the form of a pill, twice a day. Blood levels may be required to find the optimal dosage, and blood tests may also be done to monitor for side effects to the liver. The most common side effects are sedation, increased thirst and appetite, and weight gain.

Another drug that is frequently used, either alone or in combination with Phenobarbital, is Potassium Bromide. If those two medications aren’t helpful, a veterinary neurologist is sometimes consulted. Other medications that might be useful are primidone (Mylepsin & Mysoline), phenytoin (Dilantin), valproic acid (Valproate, Depekene), carbamazine (Tegretol), felbamate (Felbatol) and gabapentin (Neurontin).

the seizure threshhold

Estrogen appears to lower the seizure threshhold. If an intact female develops epilepsy, spaying may be helpful.

It is thought by some that vaccines may lower the seizure threshhold. Ask your veterinarian to individualize a vaccine program for your dog. Some measures that might be taken include separating the administration of individual vaccines by several weeks, and less frequent administration of vaccines for viral diseases.

If an epileptic dog is scheduled for surgery, be certain that the staff knows about the epilepsy. Some anesthetics may decrease seizure threshhold, so the anesthetist should choose the anesthetic accordingly.

prognosis

There is currently no cure for Primary Epilepsy in canines, but medications can decrease the frequency, duration and severity of the seizures Dogs that become epileptic prior to the age of two don’t respond to medication quite as well as dogs that develop epilepsy later in life, but small breeds tend to be more responsive to the medications than larger breeds, and in most cases, can be kept under sufficient control to enjoy a long and happy life.

Research is ongoing in hopes of finding genetic markers for Primary Epilepsy. Hopefully there will come a day when a cheek swab will tell us whether or not a particular brood bitch or stud dog carries genes for epilepsy, and the disorder will become a thing of the past. If epilepsy is a major problem in your breed, consider asking your breed club to fund research via the Canine Health Foundation.