Unfortunately, seizures are very common in dogs. Idiopathic epilepsy, the single most common canine seizure disorder, is reported to occur in anywhere from 0.5 to 5.7% of all dogs.
What is a seizure?
Seizure, convulsion, fit, epilepsy. These are terms that all describe the same thing. What happens when a sudden and uncontrolled burst of neurologic activity occurs in the brain. sometime the neurological disturbance remains localized to a small area, such as the face or one limb. Usually, however, the uncontrolled firing of neurons spreads from the brain throughout the body, causing generalized convulsions.
A seizure is not always easy to recognize, and no two look exactly alike. The typical seizure, however, might proceed as follows:
1) The dog becomes nervous or agitated, sensing that something abnormal is about to happen. Some dogs seek out their owners, looking for help and reassurance. This is called the pre-ictal period.
2) The dog begins to tremble. His eyes glaze over and he loses touch with his environment, appears blind, and will not respond to his owner's voice or touch.
3) The trembling becomes more severe and the dog stiffens. He falls, usually on his side, and begins to paddle his legs and convulse, sometimes violently. The teeth might be clenched or the dog may champ his jaws as the seizure progresses. Often, he salivates and appears not to breathe. This entire stage, the ictal stage, usually lasts less than two minutes.
4) The next stage is called the post-ictal period. The dog begins to recover, but varying degrees of neurological signs will persist. Commonly, dogs remain blind for some time after a seizure. They often pant and seem disoriented. Some dogs sleep for a long period following a seizure. The post-icial stage usually last for less than an hour, but can be considerably longer - up to two days.
What isn't a seizure?
Sometimes owners rush to the veterinarian, thinking their dog has had a seizure -- but he hasn't. Numerous conditions, some normal and some pathologies are often misinterpreted as seizures.
For example, dogs with a disease of the middle car, the vestibular nerve or vestibular nucleus of the brain can show abnormal head position and loss of balance. The onset of symptoms can be quite sudden and can be confused with seizures.
Dogs with cardiac and respiratory diseases can experience fainting episodes which leave them profoundly weak; many may fall abruptly. These dogs might pant rapidly as they try to compensate for poor oxygenation. This also is confused with seizures.
Another false alarm is a condition known as reverse sneezing, a common complaint in small animal practice. This usually affects smaller dogs and is characterized by a rapid series of violent and noisy inspirations. Often the chest and abdominal muscles will contract spasmodically during these episodes, which are always self-limiting and are of little medical significance. The cause of reverse sneezing is unknown and there is no known treatment.
Then there are those dogs who twitch or paddle their legs while sleeping. Some will even vocalize. This is especially common in young puppies although many older dogs show similar behaviour. This is normal and is usually associated with very deep sleep. Folklore has it that dogs paddling their legs during sleep are dreaming of running through an open field. Who knows? At any rate, it's not a seizure.
The biggest difference between seizures and non-seizures is the dog's state of consciousness. If a dog is doing something that resembles a seizure while conscious, is aware of it surroundings, or is easily aroused (as in sleep), it is not having a seizure.
What causes seizures?
The normal brain exists in a constantly changing state of balance between excitatory and inhibitory bioclectrical impulses. At a certain threshold point, cxcitatory activity can overwhelm inhibitory influences and a seizure can result. How far away any given animal is from this point -- called a "seizure threshold' -- is influenced by a number of factors including disease, trauma, genetics, toxins, and factors yet to be discovered. In other words, whether or not an individual dog has a seizure in response to a given stimulus depends on its own particular seizure threshold.
Many causes of seizures have been documented in dogs. In some individuals, the cause is metabolic. For example, hypoglycemia (low blood sugar) is a common cause of seizures in toy breed puppies. Hypoglycemia brought on by giving excessive doses of insulin to diabetic dogs, or by insulin-secreting tumors of the pancreas in older dogs, may also precipitate seizures. Hypocalcemia (low calcium levels) is another metabolic cause of seizures especially common in postpartum lactating bitches. Hypocalcemia and hypoglycemia are both thought to be involved in seizures seen in young puppies with intestinal parasites.
High blood ammonia levels also can lead to seizures. This metabolic disturbance is seen in dogs with liver disease (for example, portosystemic shunts in puppies). Kidney failure and high levels of circulating uremic toxins have been known to cause seizures, although this is less common.
Another important differential for seizures in dogs is ingestion of something toxic - - insecticides and rat poisons, for instance. The most common toxic cause or seizures, however, is probably lead poisoning. Dogs are exposed to toxic levels of lead from a variety of sources. 'I'hcsc include old, peeling oil-based paint, batteries, linoleum, tarpaper, roofing materials, drapery weights, fishing sinkers, champagne bottle foil and golf ball coverings, just to name a few. The amount of lead needed to instigate a seizure in a given dog depends on the dog's own seizure threshold. Seizures can also be caused by inflammation of the central nervous system (CNS), also called encephalitis. There are many important infectious causes of encephalitis in dogs. Canine distemper, for example, is one of the most common causes of seizures in puppies. Other infectious causes of neurologic disease include toxoplasma, neospora caninum, cryptococcus and rabies. Some important non-infectious causes of encephalitis are granulomatous meningoencephatitis (GME) and chronic encephalitis of Pugs (PDE).
Heat stroke is an all too familiar cause of seizures and death in dogs. Everyone knows heat stroke happens when animals arc left unattended in automobiles on a warm day, with or without the windows open. But anyone who goes to outdoor dog shows in hot weather has heard horror stories of dogs overcome by excessive beat, particularly heavily coated and/or brachycephalic breeds. Being a Pekingese owner, I never go to dog shows without plenty of ice and water on hand to prevent just such an emergency.
Congenital malformations of the CNS also can cause seizures. Examples include hydrocephalus, a disease in which fluid inside the brain does not drain properly and contributestohigh intracranialpressure,and limneephaty, a brain malformation observed in Lhasa Apsos.
Trauma to the head can lead to seizures due to hemorrhage or swelling of the brain or surrounding tissues, often with subsequent formation of scar tissue or blood clots. It is not uncommon to see seizures result from a traumatic episode that occurred years earlier. Bleeding and swelling can also be caused by tumors of the CNS or surrounding structures. Tumors are most common in older dogs.
Although there are many known causes of seizures in dogs, the most common cause remains unknown; these dogs are diagnosed as having 'idiopathic epilepsy'. Although the term idiopathic means self-originated, it's really just a technical way of saying the cause of the disease is unknown. Even though a large percentage of seizures end up being diagnosed as idiopathic, testing for other possible causes should always be performed, especially if the seizures are severe, frequent or occur in clusters. If an underlying cause is found, therapy can be directed specifically at correcting the abnormality.
Idiopathic epilepsy is believed to be an inherited disorder, at least in some breeds. Breeding studies have shown a genetic basis forthe disorder in German Shepherds, Belgian Tervuren, Keeshonden, Beagles and Dachshunds. Although inheritance patterns have not been documented, the disease also appears to be quite common in Poodles (all varieties), Saint Bernards, Irish Sellers, Siberian Huskys, Cocker Spanicls, Wirc-Haired Fox Terriers, and Labrador and Golden Retrievers.
How is the cause diagnosed?
The initial workup of a patient with seizures includes a thorough physical examination, a meticulous medical history, screening bloodwork and a urinalysis. A complete blood count can reveal signs of infection or inflammation. A chemistry profile helps to investigate metabolic causes of seizures by testing for biochemical markers of liver, kidney, glucose, and electrolyte disturbances. Changes in the urine can also reflect kidney, liver of other metabolic abnormalities. In addition, if there is any possibility of exposure, a blood sample may reveal toxic levels of lead.
If an obvious cause isn't discovered with the initial testing, further tests can prove useful. An important element in the clinical evaluation of just about any patient with a central nervous system disorder is the analysis of cerebrospinal fluid (CSF). Changes in the CSF protein concentration, blood cell population and pressure indicate specific diseases of the CNS.
CSF is collected while dogs are under general anesthesia. They are positioned on their side and an area at the base of the skull and upper neck is clipped and surgically scrubbed. Once the head is positioned just %o, a needle is carefully placed into the space between the base of the skull and the first cervical vertebra. The fluid is then collected through the needle and submitted to a laboratory for analysis. To measure CSF pressure, a manometer can be attached to the needle; pressure is often elevated in the case of brain tumors, for example.
While the patient is anesthetized, an electroencephalogram (EEG) also can be performed. Although EEG equipment is usually found only a teaching hospitals or large referral centres, the test can yield useful information.
To perform an EEG, small wire electrodes arc placed in [he skin at various points overlying the brain, and electrical activity of the brain is observed. The pins penetrate the skin, but they are very small and non-traumatic. In fact, EEGs can usually be performed in awake dogs. This test is simple and risk-free to perform (it's similar to an EKG of the heart), but interpretation usually requires the services of a specialist in neurology.
The last diagnostic option available to investigate seizures is a brain scan. Computerized tomography (CT scan) and magnetic resonance imaging (MRI) are just becoming available in veterinary medicine. These diagnostic imaging techniques yield a wealth of information and can be very sensitive indicators of structural CNS diseases. However, as with all other these scans are negative in cases of idiopathic epilepsy. Brain scans also require the use of general anesthesia.
What treatments are available?
lf the underlying cause for a dog's seizure disorder is identified, treatment can be directed at correcting the abnormality or eliminating the causative factor. Fvcn if an underlying cause is found, however, anticonvulsant drugs are commonly needed to control seizures. This is also true in the case of dogs with idiopathic epilepsy. Owners should realize that seizures are rarely eliminated completely. The goal of therapy is to reduce the frequency and severity of seizures to a level the dog and its family can live comfortably with.
Of the numerous anticonvulsant drugs available, phenobarbital is the most important and useful. With appropriate doses and periodic monitoring of phenobarbital blood concentration to ensure adequate levels, most dogs with seizures can be well controlled. The drug is safe, inexpensive and usually has to be given orally twice a day. Primidone is also used to treat seizures in dogs. This drug is converted in the bloodstream to phenobarbital and is an effective anticonvulsant. It has the additional advantage of not being a controlled substance like phenobarbital. However, primidone has been associated with more side effects and is also more costly to use than phenobarbital. In some dogs, phenobarbital alone will not control seizures. Studies arc currently underway to assess the benefits of other drugs such as potassium bromide and long-acting benzodiazcpines (valium related drugs) to control seizures refractory to phenobarbital alone. Of these drugs, potassium bromide used in combination with phenobarbital appears to be the most promising.
Dilantin is a drug used commonly in human medicine to treat epilepsy. This drug has been tried in dogs as well, but is not effective. Another familiar drug, valium, is effective in stopping seizure activity, but only momentarily. Its long term use is not recommended in dogs.
What should I do if my dog has a seizure?
Watching a dog have a seizure is a terrifying -- especially is it's a dog you love. If the dog is a young puppy or a lactating bitch, it should be seen by a veterinarian immediately. A single isolated seizure in an otherwise healthy adult dog, however, does not usually require emergency veterinary care, though an appointment should be scheduled promptly for a thorough work-up. If there are multiple seizures in a day, emergency care should be sought without delay.
When a dog has a seizure, as difficult as it may be, it is important for owners to remain calm. The dog should be moved to a safe place or laid on a rug to minimize the chances of injury. If possible, time the length of the seizure and observe carefully so that you can give a veterinarian a clear and accurate account of the event. Dogs do not swallow their tongues during seizures and owners should never put their hands near a seizuring dog's mouth. Many veterinarians believe that the length and severity of The post-ictal phase can be decreased by gently trying to calm and soothe the dog. Panicking won't help.
It's important to remember that seizures themselves are almost never fatal. When seizures occur in clusters, however, dogs are prone to developing status epilepticus, a condition characterized by continuous, uncontrollable seizure activity. Continuous seizures can lead to exhaustion,hypoglycemia, hyperthermia,oxygcn depiction, brain damage, and eventually death. Status epilepticus is an extremeemergency and often requires general anesthesia for prolonged pcriods of I inic to control.
What about my breeding program?
Epilepsy has not been proven unequivocally to be inherited in most breeds. Bear in mind, however, that the disease is more prevalent in some breeds and the finding of a higher incidence in some lines suggest that there is an inherited basis for the disorder. In addition, test breedings of epileptic dams and sires done by veterinary researchers have produced iiicidenccsofcpilepsy in the offspring rangingfrom between 38 percent (a study of three different epileptic bitches outcrosscd to a single epileptic sirc) to 100 percent (a mating of two epileptic siblings). These studies provide strong evidence of an inherited basis for epilepsy in dogs. Epilepsy has been shown to be an inherited disorder in hunians, baboons, mice, rats, rabbits, gerbils and chickens. It makes sense that it is probably inherited in dogs.
It also makes sense that epileptic dogs, and probably their littermates, should not be used for breeding. And it would be unwise to repeat a breeding that resulted in an epileptic dog. With good veterinary care, and with attentive care at home, most epileptics can make perfectly good pets.
Hopefully, future investigations will uncover more of the facts about epilepsy in dogs. For now, it seems, there are probably more questions than answers.
Cunningham, J., Farnbach, G.C., Inheritance and idiopathic epilepsy. I Am Anim Hosp Assoc 24:421-424, 1988.
Delahunta, A. Seizures-convulsions. Veterinary Neuroanatomy and Clinical Neurology (second ed.), W.B.
Saunders Co., Philadelphia, 1983, pp326-343.
Kornegay, J.N., Lane, S.B. Seizures. In Fttinger S.3. (ed), Textbook of Veterinary Internal Medicine (third ed.) W.13.
Saunders Co., Philadephia, 1989, pp66-69.
Lane, S.B., Bunch, S.E. Medical management or recurrent seizures in dogs and cats. J. Vet Intern Med 4:26-39,1990.
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