Epilepsy is a disorder of the brain that causes disorganised electrical activity and fits.  A small percentage of dogs are affected without any identifiable cause.  There is no cure but although it can be difficult to treat there are various treatments available which can help reduce the severity and frequency of the attacks.  Signs that a dog may be about to have a seizure include him getting anxious, being unusually quiet, getting restless or acting in a strange manner.

Canine Epilepsy seizures can range from Mild to Grand Mal and can be life threatening.  If a dog is diagnosed by a veterinarian as being epileptic, there are various treatments in use, such as:

Phenobarbital
Potassium Bromide
Primidone
Valium
Dilantin
Gabapentin

Diet can play an important role in controlling epilepsy as some preservatives can cause seizures.  Dogs should also be kept away from as many chemical pollutants as possible.  If you suspect that your dog has had a seizure contact your vetenarian.

 

Canine Idiopathic Epilepsy

First published in Australian Shepherd Journal, vol 13 issue 4, July/August, 2003
by Margaret Muns, DVM
 

INTRODUCTION
Seizures are the most common neurologic symptom seen by small animal veterinarians. They can be caused either by problems inside the brain, or outside. Discussing all the types of seizures and their causes is way beyond the scope of this article. Instead, the paper will cover the most common cause of canine seizures, namely canine idiopathic epilepsy. Although idiopathic epilepsy can affect many breeds, (including mongrels) there is strong evidence for genetic involvement. Therefore, affected animals should not be bred.

TERMINOLOGY
In order to fully understand idiopathic epilepsy and what it entails, owners first need to be aware of some basic terminology. To begin with, the terms "seizure", "convulsion" and "fit" are interchangeable. They all can be used simultaneously to describe a sudden, temporary rhythm disturbance affecting the cells in a dog's brain. Clinically, the appearance of the seizure depends on the area the brain affected and the severity of the disturbance.

The term "epilepsy" is used by most researchers to describe seizures of any cause. Epilepsy can be further characterized as being either primary or secondary. Primary epilepsy (also called idiopathic, genetic, true or inherited epilepsy) is probably caused by biochemical defect in the brain cells or their environment. Typically, there's absence of any structural damage on microscopic exam of the brain. An affected dog will have normal physical, neurologic and laboratory examinations during the time intervals between seizures. As will be discussed later, there's also substantial evidence for a genetic influence on the development of primary epilepsy in dogs. By contrast, secondary epilepsy (also called acquired or symptomatic epilepsy) occurs secondary to some kind of brain damage. The damage can be a consequence of prior trauma, circulatory disorders, infections, congenital defects, or metabolic diseases. Dogs affected with secondary epilepsy are much more likely to have abnormalities on physical examination and diagnostic testing.

Being able to understand and recognize the types of seizures that can occur is also very important. Generalized seizures are the most frequently recognized type of seizure in canine patients. They are also the type of seizure seen most frequently in dogs affected with idiopathic epilepsy. The initial trigger area (or seizure focus) may only be a small number of unstable brain cells. However, when they discharge abnormally, they make the surrounding cells discharge erratically. As a result, the seizure spreads throughout the brain and becomes generalized. The net result is symmetrical involvement of the dog' s entire body. This type of seizure is most commonly called a tonic-clonic or grand mal seizure. During a generalized seizure, the dog usually falls over and loses consciousness. Shortly afterwards, there is involuntary extension of the limbs (tonic phase), followed by paddling (clonic phase). The animal may grind its teeth, salivate, urinate and defecate during the seizure. The pupils of the pet's eyes are also usually dilated. Some dogs only have milder generalize seizures. These tend to be less dramatic with the animal remaining conscious during the events. However, during the seizure, the dog may act anxious, stumble, or fall over. But there are usually no jerking motions of the limbs, head or trunk. In the past, owners have called these types of mild generalize seizures "petite mal seizures". However, this is not a correct use of the term based on the definitions used in human medicine.

Partial seizures occur when only one portion of the brain is discharging abnormally. The clinical symptoms observed depend on what areas of the brain are involved in the seizure activity. Partial seizures are most commonly the result of local or multifocal damage to the brain. Such damage can occur after trauma, infection, circulatory disorders, or cancer. If the focus of the seizure happens to be in an area the brain responsible for controlling behavior, bizarre behaviors may be only symptoms seen. In such cases, there will be no abnormal body motions. The proper term to describe these types of events is psychomotor epilepsy .

CAUSES OF IDIOPATHIC EPILEPSY
Most experts agree that the seizures associated canine idiopathic epilepsy are primarily caused by a functional disturbance of the cells of the brain. However, the factors responsible for initiating the disturbance are not well understood. Understanding is hampered by the brain's susceptibility to a wide variety of structural and metabolic insults. Researchers are able to investigate the pathologic consequences following injury in disease because these types of injuries can be created and then studied in the lab. Unfortunately, this can't be done for idiopathic epilepsy because there aren't any detectable structural or biochemical changes in the brains of affected dogs. Consequently, is impossible to create research models. Without such models, the ability to fully understand the nature of a disease is greatly hindered.

Fortunately, one concept that is well understood is that of the seizure threshold. In order for the nervous system to work properly, there must be coordinated transmission of impulses from one cell to the next. Most of the cells in the canine brain are excitatory neurons. Basically, one neuron receives impulses from its neighbor before transmitting them to the next one in the "circuit�. The remainder of the neurons in the brain are inhibitory neurons. These brain cells help to control and contain the impulse so that spread of erratic impulses throughout the brain does not occur. This is a very fine line of control. Seizures can be triggered if something happens to tip to scale in the wrong direction. The point at which this occurs is the seizure threshold.

Every animal has its own individual seizure threshold. Seizures can be induced in any individual dog given the right set of circumstances. However, things that can induce seizures in one animal won't do it in another. Animals with lower seizure thresholds may have brain cells that are inherently more hyper excitable than other animals. In the case of canine idiopathic epilepsy, genetic influences are presumed to influence a particular animal's seizure threshold . Affected animals may have a more diffuse or multifocal state of neuron excitability. This may be due to the result of early congenital events that become magnified over time.

DIAGNOSIS
The first step in evaluating any dog presented for seizures is to carefully review the history and physical exam. This is critical because of the high number of seizure dogs with normal laboratory findings. In many cases, a veterinarian can rule out several possibilities just by knowing the age of the dog at the time the seizures began. Dogs with idiopathic epilepsy will usually have their first seizure between 1-5 years of age. Any dogs with seizures beginning at either younger than one year, or older than five years will typically have some kind of underlying disease process going on.

A complete and thorough diagnostic evaluation is always indicated no matter how old the dog is when the seizures began. Obtaining a definitive diagnosis of canine idiopathic epilepsy is impossible for the most part. Usually, a veterinarian arrives at this conclusion through a process of elimination. In other words, all other possible underlying causes for the seizures are first eliminated before settling on the diagnosis of idiopathic epilepsy. Table 1 outlines the circumstances under which a diagnosis of canine idiopathic epilepsy is appropriate. If at any time a dog with presumptive idiopathic epilepsy develops other symptoms, or becomes unresponsive to therapy, the diagnosis must be re-evaluated .

TABLE 1: Criteria used to Establish a Diagnosis of Canine Idiopathic Epilepsy (3)

Generalized seizures 
Onset of seizures between 1-5 years of age 
Normal physical, neurologic exams 
Normal laboratory data 


TREATMENT
For treatment of canine idiopathic epilepsy to be successful, owners must be properly educated. This is because success of therapy depends more on the dog's owner than any other factor. Seizures can be frightening. Therefore, owners are naturally anxious about their pet's condition. The best way to defuse this anxiety is by making sure the owners have the facts they need to deal with the disease. They must understand that the main objective of treatment for canine idiopathic epilepsy is to achieve control and not a cure. Dogs with idiopathic epilepsy are controlled when there is a reduction of seizure frequency and intensity with a minimum of side effects. Consequently, animals receiving treatment will still continue to seizure no matter what drugs or doses are used. The seizures just won't be as frequent, or as severe as they were before treatment began. Most clinicians initially aim for a 50 percent increase in the interval between seizures or one isolated seizure every 6-8 weeks. Once this is achieved, attempts can be made to obtain longer intervals. Approaching treatment this way allows for the setting of mini-goals. As these goals are reached and exceeded, the owner can then get a sense that progress is being made.

In addition to understanding the meaning of control, owners must also be aware of several other facts about seizure treatment. Before beginning therapy, the owner must clearly comprehend the advantage and disadvantages of treatment. Seizure therapy is not benign therapy. It involves using drugs that can cause significant side effects. Owners must know what medications are being prescribed, what doses are being used, and what side effects to expect. They must be willing to keep a diary or seizure log to document when the seizures occur, how long they are, what medication is being used, and any other relevant comments. This is so the veterinarian can have an idea what's happening at home. Owners must be given guidelines so that they know what to do in the event of a seizure. They must also understand which types of seizures are dangerous, so that timely emergency treatment can be sought. But above all, owners must know that there are no shortcuts allowed when treating dogs for idiopathic epilepsy. The medications must be given consistently, or not all. Any sudden drop-off in medication can trigger life-threatening seizures in affected patients. Therefore, any changes in drug type or dosing must only be done under the supervision of the pet's veterinarian.

DRUG THERAPY
Antiepileptic drug therapy is usually begun when the interval between isolated seizures is less than 6-8 weeks. Idiopathic epilepsy in dogs is a paroxysmal disease. This means that symptoms occur sporadically and are very difficult to predict. Consequently, spontaneous variations in seizure frequencies can be expected to occur in each patient. If a dog is started on treatment after the first seizure, it will be impossible to evaluate the overall seizure pattern. Therefore, monitoring the response to treatment will be very difficult. The exception to this rule is those animals that present with status epilepticus as their first seizure episode. Status epilepticus is defined as a state of constant seizure activity with no interruption. This is a dangerous condition and a medical emergency. Another exception to the general guidelines for treating seizures is those animals that present with multiple clusters of seizures occurring over a 24-72 hour period. These animals also need prompt treatment to prevent the development of status epilepticus.

Phenobarbital is the initial drug of choice for managing idiopathic epilepsy in dogs Veterinarians do not have a lot of choices when selecting anticonvulsant medications. Many of the human anticonvulsant drugs available can't be used for long-term control in dogs because of their short duration of effect. As a result, these drugs cannot produce good serum concentrations. Many of the human drugs currently available also can be toxic when used to treat dogs.

Low doses of phenobarbital are usually used when therapy is begun. Afterwards, the dose is slowly increased until either desired control is obtained, or unacceptable side effects occur. Common side effects of phenobarbital therapy include sedation, increased thirst, increased urination, and increased appetite. Although the symptoms can be worrisome, most dogs will develop tolerance in 1-2 weeks. Another important side effect of phenobarbital therapy is liver toxicity. Most dogs receiving long-term phenobarbital therapy will have moderate increases in their liver enzymes. However these increases usually occur without serious damage to deliver function.

Frequent monitoring of blood phenobarbital levels is very important during initial treatment of idiopathic epilepsy. To some extent, the final therapeutic dose for any given dog has to be determined by trial and error. Every dog has a different metabolic rate. So there is a lot of variability in the serum concentration of phenobarbital that can be achieved by any given dose in any given dog. As a result, dogs need to be monitored frequently during initial treatment so that the dose can be adjusted as needed to get good serum phenobarbital concentrations. Once the dog is controlled, serum phenobarbital levels are typically monitored every six-twelve months. Some authors recently have advocated monitoring only when clinically indicated. Their argument is that the numbers currently used to define the therapeutic range are not accurate enough since they are extrapolated from human data. As a result, a low serum phenobarbital level might be enough to control some dogs, while others need much higher levels. Owners need to be aware of this so that a veterinarian unfamiliar with the case doesn't raise or lower the dose indiscriminately based on the numbers on a page. Instead, changes in dosing should be based on the whole clinical picture. If a dog is showing good control on blood phenobarbital levels that are below the ideal therapeutic range, the dose should not be increased just to get the values within the excepted range.

REFRACTORY EPILEPSY
Approximately 60-80 percent of dogs with idiopathic epilepsy can be controlled with minimal side effects using phenobarbital alone. Refractory epilepsy occurs when a dog continues to have seizures at an unacceptable rate and severity despite good serum phenobarbital levels. However, before diagnosing refractory epilepsy, factors that can complicate phenobarbital treatment must be investigated and eliminated. The veterinarian must be sure that the owner has been properly educated. He/she should make sure that an effective dose drug is being used at an adequate dose. The possibility of liver dysfunction must also be considered. In rare occasions, an animal may develop severe or even fatal liver toxicity secondary phenobarbital treatment. Once a diagnosis of refractory epilepsy is made, then combination therapy can be instituted. Combination therapy will enable another 10-15 percent of canine epileptics to achieve control without significant side effects. Currently, the drug of choice to use in combination chemotherapy for canine idiopathic epilepsy is potassium bromide.

Bromide belongs to a group of chemicals called the elemental halides. It has significant sedative and anticonvulsant effects. Bromide was first used as a human anticonvulsant during the mid 1800s. In fact, it was the drug of choice for human epilepsy for more than half a century. However, because of the chemical's low safety index, its popularity decreased in the early part of this century when phenobarbital was introduced. Even so, bromide was still used as a sedative in both prescription and over-the-counter sleep aids and headache remedies until as recently as the 1960s. Today, bromide use in human medicine is limited mostly to treatment of children with resistant epilepsy. Is especially useful for kids with early onset of seizures, or underlying organic brain disease. Since it is not longer widely available, veterinarians can only get bromide from custom veterinary compounding pharmacies, or from chemical supply houses.

Recent clinical studies have shown that combination therapy with potassium bromide and phenobarbital can help many dogs that are resistant to phenobarbital alone. More than half of the dogs with refractory epilepsy will have a reduction in the frequency and severity of seizures after potassium bromide is added. Adding potassium bromide is also useful for those dogs experiencing unacceptable side effects with phenobarbital therapy. In such cases, adding potassium bromide can lead allow the veterinarian to lower the phenobarbital dose without sacrificing control. Lastly, potassium bromide can be used successfully as a single agent in dogs with pre-existing liver disease. Some doctors have even gone as far as to routinely use potassium bromide as a first choice drug. However, studies have not been done to confirm that bromide can work well alone as a first choice therapy.

Use of potassium bromide to treat canine idiopathic epilepsy is not risk free. Adverse effects associated with potassium bromide administration include increased urination, increased thirst, increased appetite, sedation, balance disorders and hind limb weakness. These side effects are enhanced by concurrent phenobarbital administration. They usually resolve if the phenobarbital dose is reduced by 10-30 percent. If the adverse reactions don't resolve, or become more severe, serum bromide concentrations need to be checked. Bromide concentrations should also be routinely monitored 6-8 weeks after initiating therapy to determine if any initial dose changes need to be made.

OUTCOMES
Canine idiopathic epilepsy is a chronic disease. Subsequently, long term, or even life long therapy is needed to control the seizures. Although rare, remissions are possible. Remission is defined as a period of 1-2 years without a seizure. Unfortunately, it is impossible to predict which dogs will go into remission and which won't. Animals may be candidates for drug withdrawal once they have gone at least 8 months- 1  years without a seizure. These animals may be slowly removed off of therapy over a period of another 6 months to 1 year. If drugs are withdrawn sooner, the dog may relapse with breakthrough seizures or status epilepticus. Dogs most likely to relapse will either do so during withdrawal, or within 1-2 months of stopping the medication altogether.

REFERENCES
Shell LG: Understanding the Fundamentals of Seizures. Veterinary Medicine. July 1993. 622-627.
Shell, LG: The Diagnostic Approach to Seizures Veterinary Medicine. July 1993. 641-646.
Thomas, WB. Managing Epileptic Dogs. The Compendium on Continuing Education for Practicing Veterinarians. Vol. 16, No. 12. December 1994. 1573-1578.
Trepanier, LA. Use of Bromide As an Anticonvulsant for Dogs with Epilepsy JAVMA, Vol.207, No.2, July 15, 1995. 163-166
March, P. A. Seizures: Classification, Etiologies, and Pathophysiology Clinical techniques in Small animal practice. Volume 13, No. 3, August 1998. 119-131.
Knowles K. Idiopathic Epilepsy. Clinical Techniques in Small Animal Practice. Volume 13, No. 3. August 1998. 144-151.
Dyer KR, Shell LG. Anticonvulsant Therapy: A Practical Guide the Medical Management of Epilepsy in Pets. Veterinary Medicine. July 1993. 647-653.
 
reprinted with kind permission from Sheila Dolan
Managing Editor, the Australian Shepherd Journal
http://www.ashgi.org