Seizure Disorders

SEIZURE DISORDERS

By Geneva Coats
Your dog develops a far-away look in his eyes, suddenly collapses and begins to tremor and shake uncontrollably. Before you have a chance to react, the incident is over. He remains lethargic and weak for a while afterwards. What happened?
Seizures, epilepsy, "fits", convulsions, all different terms referring to the same condition.
A seizure results from sudden uncontrolled abnormal firing of neurons in the brain. The brain exists in a delicate state of chemical and physical balance. This balance can be upset by a number of factors. If the balance in the brain shifts too far, brain cells (neurons) may become over stimulated, and a seizure may result. This point at which seizures occur is known as the "seizure threshold".
Seizures are commonly preceded by an "aura" or altered state which may be characterized by restlessness, nervousness, salivation, and anxiety. The "ictus" or actual seizure follows next. The dog will become nonresponsive, collapse, and experience involuntary motor movements such as stretching, kicking, or paddling. The motions may vary in intensity from mild tremors to severe jerking movements. Seizures place tremendous stress on the heart, lungs and circulation. The body temperature may get very high from all the muscle activity, and the animal may not breathe adequately. This may result (in rare cases) in brain damage and death. The actual seizure itself may last only seconds or minutes. A seizure persisting more than a few minutes is an EMERGENCY, which requires immediate treatment by the closest veterinary facility. The postictal stage is the period of time after the seizure; the dog may remain lethargic and weak, and possibly disoriented.
To be considered a true seizure, there must be an alteration in the level of consciousness. If the dog is conscious, responsive, aware of his surroundings, or is awakened easily from a sleep state, he is not having a true seizure. Heart and lung problems can sometimes result in weakness and collapse, and middle ear infections can cause dizziness. Twitching and jerking motions may occur in a sleep state, and this is considered normal in early neurological development of puppies.
There can also be focal or partial seizures, which affect a certain part of the body. For instance, the face or just one limb may be involved. This may progress to involve the entire body. The fact that the seizure starts in a local area suggests that a specific area in the brain is damaged, perhaps due to a brain tumor or infection.
Seizures are a sign of irritation of the brain tissue, just as a coughing is a sign of irritation of the respiratory tract. Any of the factors listed below can trigger uncontrolled firing of the neurons of the brain. When a seizure is the result of an identifiable cause, the disorder is known as symptomatic or secondary epilepsy. Seizures may be caused by any of the following:
Brain tumor-more common in dogs over 5 years old.
Head injury
Stroke-can be caused either by bleeding in the brain or bydeficiency of the blood flow to the brain tissue. Either condition can be associated with seizures.
Hypoglycemia or low blood glucose (sugar)-common in toy breeds and especially puppies. Rubbing a small amount of sugar or syrup on the lips, gums and tongue may be effective in stopping the seizure if caused by low blood sugar.
Hypoxemia - Low blood oxygen, with resultant lack of oxygen available to the brain. This can be due to poor lung function, or an abnormal cardiac or pulmonary shunting process in a youngster.
Elevated blood ammonia level due to liver infection, cirrhosis or a liver shunt.
Inflammatory or infectious disease of the nervous system. This can include Lyme disease, distemper, rabies, toxoplasmosis, and Rocky Mountain spotted fever, encephalitis and meningitis.
Ingestion of toxins such as lead, caffeine, chocolate
Botulism-toxins sometimes produced by a bacteria in food.
Exposure to pesticides such as organophosphates (many flea control products) and metaldehyde (snail bait)
Congenital problems, such as hydrocephalus, which produce increased intracranial pressure.
Intestinal parasites, which can cause severe anemia and hypoglycemia. Some parasites also migrate to the liver and brain in their larval forms.
Low serum calcium or magnesium levels- for example, eclampsia in a lactating bitch.
Blood sodium or potassium imbalances. This can be caused by dehydration or kidney problems.
Genetic predisposition as in the MDR-1 mutation common to many herding breeds. This mutation causes a lack of the protein which exerts a protective function in the blood-brain barrier and limits the entry of many drugs to the central nervous system. The lack of this protein renders the dog susceptible to the neurotoxic side effects of several drugs including Ivermectin, Moxidectin and Loperamide.
Kidney failure and high levels in the blood of uremic toxins
Hyperthermia as a result of fever or heat stroke
Thyroid hormone deficiency or hyperactive thyroid.
Seizures are a common disorder in dogs. When tests are done and no reason can be found for the seizure, the disorder is referred to as "idiopathic epilepsy". The term "idiopathic" means that there is no cause for the problem, and that the seizures are not the result of another disease process. This is the type of epilepsy which is usually considered to have an inherited basis.
Idiopathic epilepsy is the most common canine seizure disorder, occurring in up to nearly 6% of all dogs. The problem is more prevalent in some breeds than others. There is a suspected genetic basis for idiopathic epilepsy in German Shepherds, Belgian Tervurens, Keeshonden, Beagles, Dachshunds, Pugs, Poodles, St. Bernards, Irish setters, Siberian Huskies, Cocker Spaniels, Wire-Haired Fox Terriers, Labrador and Golden Retrievers, and Australian Shepherds. In breeds which are genetically predisposed, up to 14% of the population may develop epilepsy. As epilepsy has been shown to be an inherited disorder in humans, baboons, mice, rats, rabbits, gerbils, and chickens, it seems logical that is can be an inherited disorder in dogs as well. Test breeding of epileptic dams and sires done by veterinary researchers have produced incidences of epilepsy in the offspring ranging from between 38% (affected to nonaffected) to 100% (breeding together of two affected dogs).
Hereditary epilepsy commonly begins between the ages of 1-3 years. Seizures which begin earlier or later in the dog's life most probably are a result of a disease process such as those listed above. Your vet will likely want to rule out these conditions before deciding that your dog has hereditary epilepsy.
If your dog has a seizure, don’t panic. Check the clock and make a note of how many seconds or minutes the seizure activity lasts. Keep your dog in a safe environment until the seizure is over. Note what type of abnormal muscular activity happens, so you can describe it for your vet. Do not put anything in your dog’s mouth. Remain by your dog to comfort him. Call your vet for further advice. If the seizure lasts more than a few minutes, take your dog to the closest veterinary facility for immediate care. If your dog has recurrent seizures (more than once in 24 hours), again, seek immediate medical assistance.
Determining the cause is essential for making appropriate treatment choices, and to assist in breeding decisions. You should seek the advice of your veterinarian. Your vet will obtain a medical history, and a full exam including a neurologic exam. He will do blood tests, a urinalysis and fecal exam to look for any possible cause for the seizures. Other exams may include x-ray or ultrasound of the abdomen, EEG to evaluate brain waves, skull x-ray or head MRI, and a cerebrospinal fluid analysis if infection is suspected. Treatment will depend upon the cause of the seizure.
In the case of idiopathic epilepsy, if your dog experiences seizures more frequently than once a month, your vet may decide to place your dog on seizure medication. Antiepileptic drugs do not cure epilepsy, they simply control the seizures. Life-long therapy may be expected. The drugs increase inhibition in the brain, decrease the seizure threshold, and thus make seizures less likely. This often results in side effects such as sedation, uncoordination of movements and appetite stimulation. These effects lessen with time as the body becomes habituated to the medication. The number of dogs who have serious side effects from the medication is small, and often preventable through careful health monitoring. Regular rechecks are essential, and a thorough physical should be done at least yearly.
Phenobarbital and Primidone (Mysoline) are considered first line drugs for idiopathic epilepsy. They are eliminated by the liver and over time may cause liver damage. Your vet will want to monitor liver function tests on a regular basis to avoid this problem. Also blood levels of these drugs are checked to help with deciding on the dosage required. Bone marrow depression and anemia may occur, so a blood count should be done yearly as well.
Potassium Bromide can be used in dogs. Interestingly, it is not well tolerated by humans, as it causes psychological problems in people. However, this is not a problem for dogs. Salty foods should not be given with bromide. Bromide can be mixed with food, as it sometimes can cause an upset stomach.
Valium (diazepam) is affective in treating the acute phase of seizure activity. It is not as effective when given routinely, and is usually reserved for emergency situations.
Many of the newer antiepileptic drugs, such as Dilantin, Tegretol, and Depakote, are metabolized more quickly by dogs than humans. The need for frequent dosing (and their higher price tag) makes their use impractical for dogs.
Unless the seizures are due to low blood sugar or low oxygen due to heart/lung disease, there is no reason to restrict activity. Most epileptic seizures occur when the pet is relaxed and quiet, or even sleeping. Most epileptic pets can lead relatively normal lives with careful monitoring, a healthy diet, plenty of fresh air and exercise, and their favorite human nearby.
References
Davol, Pamela A. "Understanding Canine Epilepsy"
Dvorak, Roy, "Why Does My Dog Have Seizures"
Graves, Thomas K, DVM, "Seizures in Dogs"
O'Brien, Dennis, DVM, PhD., "Understanding Your Pet's Epilepsy"
Primovic, Debra, DVM, "Seizure Disorders"
Copyright 2006. This article may not be reproduced or distributed in any form without express written consent of the author.