Epilepsy in Dogs
Epilepsy is a recurrent seizure disorder that may be idiopathic or acquired. Acquired epilepsy has an identifiable cause, such as a mass of scar tissue in the brain following a head injury. Idiopathic epilepsy occurs in up to 3 percent of dogs and accounts for 80 percent of recurrent seizures. The cause is unknown, although an imbalance in chemicals that transmit electrical impulses in the brain has been suggested. Seizures, usually of the grand mal type, begin between 6 months and 5 years of age.
Breeds in which the condition is inherited include Beagles, Dachshunds, Keeshonden German Shepherd Dogs, Belgian Tervurens, and others. Breeds with a high incidence, but in which inheritance has not yet been established, include Cocker Spaniels, Collies, Golden Retrievers, Labrador Retrievers, Irish Setters, Poodles, Miniature Schnauzers, St. Bernards, Siberian Huskies, and Wire Fox Terriers. Even mixed breeds can be afflicted with epilepsy.
If the diagnosis is truly epilepsy, the attacks must be recurrent and similar. Epileptic seizures usually become more frequent with time. Your veterinarian will ask you to keep a log of the frequency of seizures and to provide a description of the dog's behavior before, during, and after each seizure.
A typical epileptic seizure has three phases: an aura, a generalized grand mal seizure, and a postseizure state-as described in the previous section. All three phases may not be seen, because many seizures occur while the dog is resting or asleep. Furthermore, in some cases the seizure is atypical. Instead of a classic grand mal convulsion, the dog exhibits strange behavior such as frenzied barking, licking or chewing at herself, staring into space, or snapping at invisible objects. This is called a psychomotor seizure and is believed to arise from a center lower in the brain (not the cerebrum).
Focal motor seizures, as already discussed, indicate a lesion in the brain. An abnormal neurological exam or EEG during a period when there have been no recent seizures also indicates a lesion in the brain. These findings eliminate the diagnosis of epilepsy. Further diagnostic tests include a spinal tap with cerebrospinal fluid analysis, skull X-rays, and a CT scan or MRI.
Treatment: A number of newer drugs are available for treating epilepsy. However, anti-epileptic drugs, either singly or in combination, are not 100 percent effective. The best one can hope for is that treatment will significantly decrease the number and severity of the seizures while increasing the seizure-free interval between them. In general, treatment is indicated if there are two or more seizures a month, or more than 10 to 12 seizures a year. Cluster seizures and status epilepticus are other indications to start treatment.
Phenobarbital continues to be the single most effective drug for treating epilepsy in dogs. Its principal initial side effect is sedation. Most dogs, however, develop a tolerance to the sedative effects within a few weeks. In some dogs, it can cause liver damage. Potassium bromide can also be used to treat epilepsy. More dogs respond to phenobarbital than to potassium bromide alone, but potassium bromide has no potential to cause liver damage. Rarely, it will cause hind leg stiffness, but this is reversible if the drug is stopped. Many dogs are best controlled by a combination of phenobarbital and potassium bromide. A few dogs are well controlled on potassium bromide alone.
If seizures cannot be controlled with phenobarbital and potassium bromide, other drugs, such as Clonazepam, Valproic acid, Clorazepate, and many others can be added. The dosages and rates of action of all anticonvulsants are variable. Regular monitoring of serum drug levels is essential-both to control seizures and to avoid toxicity. Liver enzymes are monitored as well. The two common causes of treatment failure are not maintaining adequate drug levels and not giving the drugs as often as directed. A missed dose of an anticonvulsant can precipitate a seizure. It is important to work closely with your veterinarian.
Acupuncture and dietary changes may also help to reduce the number and extent of seizures.
Research is under way to identify the defective gene or genes responsible for epilepsy so that dogs can be identified as carriers before being bred. Affected dogs may not have their first seizure until 3 to 5 years of age, by which time they may have already been bred. No dog known to seizure from suspected epilepsy should be bred.
This article is excerpted from “Dog Owner’s Home Veterinary Handbook” with permission from Wiley Publishing, Inc.
Copyright © 2007 by Howell Book House. All rights reserved.