Seizures in Pets

 The diagnosis and treatment of seizure disorders in small animals are similar in many respects to the diagnosis and treatment of other ailments: a historical problem arises, a therapy is started to treat the underlying disease and/or signs of the disease. In seizure disorders, however, unlike other diseases, a long period of normal activity may occur between the seizure event. Even during these normal periods, serious conditions may still be present as the cause of the seizures. Knowing which animals are at the highest risk for such problems is helpful in planning the proper tests and treatment.

First, your veterinarian wants to be sure that an epileptic seizure has occurred and, if so, the seizure type(s) manifested. An epileptic seizure is the clinical sign of excessive, abnormal activity in the brain and the clinical features can be separated into three components. The aura is the initial manifestation of a seizure.

During this time period, which can last from minutes to hours, animals can exhibit recurrent pacing or licking, excessive or unusual salivation or vomiting, and/or even unusual psychic events such as excessive barking or increased or decreased attention seeking. Some owners even report that they know their dog is going to have a seizure days in advance by changes in the animal's behavior. The ictal period is the actual seizure event, manifested by involuntary muscle tone or movement and/or abnormal sensations or behavior, usually lasting from seconds to minutes. After the ictal event is the postictal period. During this time, an animal can exhibit unusual behavior, disorientation, inappropriate bowel or bladder activity, excessive or depressed thirst and appetite, and actual neurologic problems, such as weakness and blindness.

Seizure types can be classified into two major categories: partial and generalized. Partial seizures are the result of a focal abnormal electrical event in the brain. This seizure type is associated with a higher prevalence of focal disease, such as a tumor. Animals with simple partial seizures have a sudden change in activity without any change in awareness, such as twitching of facial muscles. Animals with complex partial seizures often show bizarre behavioral activity, such as "fly-chasing" behavior patterns. Generalized seizures are either convulsive ("grand mal") or nonconvulsive ("petit mat") seizures. Generalized convulsive seizures are by far the most common seizure type seen in animals and are characterized by impaired consciousness coupled with symmetric stiffening, paddling, or even loss of movement of the limb muscles. The major form of nonconvulsive seizure is the "absence" variety, manifested as a "spacing-out" episode. The severity of the seizure does not necessarily match the cause, as dogs with brain tumors may have mild partial seizures and dogs with primary epilepsy may have severe generalized seizures.

The second level of assessment is the diagnosis of the cause of the seizures. Just as a cough signals a problem in the airway, a seizure tells us there is a problem in the brain, but not the cause. The goals of a diagnostic evaluation are to determine the underlying cause, evaluate the chance for recurrence, and establish whether medication is necessary for treatment. Primary epileptic seizure (PES) is diagnosed if no underlying cause of the seizure can be identified (idiopathic). This term is often reserved for inherited epilepsy in people, but the genetic component of epilepsy is difficult to determine in many animals. Breed-related inherited epilepsy in the dog has been documented in beagle, Belgian Tervuren, keeshond, dachshund, and Siberian husky dogs. Other breeds with a high prevalence of an inherited component of their seizures are German shepherd, border collie, Irish setter, and golden retriever dogs. A diagnosis of PES is most common in large breed dogs 1 to 5 years of age and/or when the interval between the first and the second seizure event is long (>4 weeks).

Secondary epileptic seizure (SES) is the direct result of an abnormal brain structure. The conditions involved include developmental brain problems, inflammation, tumors or strokes. An animal is categorized as having epilepsy if recurrent PES or SES is diagnosed, indicating the presence of a chronic brain disorder.

Reactive epileptic seizure (RES) is a reaction of the normal brain to transient systemic insults or physiologic stresses. A patient with recurring RES is not defined as having epilepsy, as there is not a primary chronic brain disorder underlying the seizure activity. An underlying identifiable cause (SES or RES) of the seizures is suspected in dogs that have an initial seizure when they are younger than 1 or older than 5 years of age, the initial interval between the first and second seizure events is less than 4 weeks, or a partial seizure is the first observed seizure. Cats, in general, do not suffer as frequently from seizures as dogs. When cats have seizures, there is a high likelihood that an underlying problem in the brain (SES) is present, such as inflammation, stroke, or tumor.

Maintaining a seizure-free status without unacceptable adverse effects is the ultimate goal of antiepileptic drug (AED) therapy. This is optimal balance is achieved in less than half of epileptic people and, probably, just as many dogs. Before starting AED treatment, owners and veterinarians should have a realistic idea of what to expect over the course of therapy. First and foremost is that seizure control does not equal elimination. Decreasing the number and severity of seizures and postictal complications, while increasing the time period between seizures, is a realistic goal. Once treatment is started, you should realize that there is a daily treatment regimen, reevaluations are required, and there is a potential for emergency situations to arise, along with the inherent risks of the drug.

The decision to start AED therapy is based on the underlying cause, seizure type and frequency, and postictal effects. An acceptable AED is one that can be given two to three times per day, has documentable benefit, is well tolerated, and has few side effects. The two AEDs most widely used in the dog and cat are phenobarbital and potassium bromide. Bromide has the benefit of a reduced chance of liver toxicity but may not be as effective as phenobarbital for stopping all types of seizures or work as quickly. Periodic measurements of the amount of drug present in the bloodstream are necessary to determine that an acceptable level of medication is present. At the same time, blood test to evaluate liver function may be necessary.

These periodic evaluations are important in trying to maximize the benefit of drug therapy while monitoring for early detection of possible complications. Treating each animal as an individual, applying the philosophy that seizure prevention is better than intervention, and consulting your veterinarian to help formulate or revise treatment plans increase chances of success.

The above is general veterinary information. Do not begin any course of treatment without consulting your regular veterinarian. All animals should be examined at least once every 12 months.

About the author:

From the Textbook of Veterinary Internal Information: Client Information Series. Copyright © 2000 by W.B. Saunders Company. All rights reserved.

Linda Mar Veterinary Hospital and its cat-only affiliate, Coastal Cat Clinic, are small animal practices located in Pacifica, California. To find a veterinarian or to learn more about the vet clinic and our staff, visit:[http://lindamarvet.com/]

 Michael Podell, DVM