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:
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
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.
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
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.
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)
Onset of seizures between 1-5 years of age
Normal physical, neurologic exams
Normal laboratory data
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.
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
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.
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
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.
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.
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reprinted with kind permission from Sheila Dolan
Managing Editor, the Australian Shepherd Journal