Seizures
This
information is not meant to be a substitute for veterinary care. Always follow
the instructions provided by your veterinarian.
A seizure is defined as a paroxysmal, transitory
disturbance of brain function that has a sudden onset, ceases spontaneously,
and has a tendency to recur. Epilepsy is a recurrent seizure disorder
irrespective of cause. Generalized seizures affect the entire body. Most
commonly, dogs will fall to the side, make paddling movements with the limbs,
and often will urinate, salivate and defecate. Seizures usually last less than
90 seconds. Focal seizures remain
localized to one body region. Seizures may start focal and then become
generalized. Information about where the seizure activity begins is
of value in localization of the seizure focus to one side of the brain. The
seizure focus is the point in the brain from which the seizure begins.
After the veterinarian is convinced that a seizure
disorder is present, the most important question to be answered is whether the
seizure focus is the result of primary brain disease (intracranial), the result of
a disturbance outside the brain (extracranial), or is occurring idiopathically (without obvious
cause). Initially the causes for seizures, should be categorized into those
secondary to an intracranial structural cause, an extracranial cause
(metabolic), or an unknown cause (idiopathic).
Metabolic: Extracranial disease
resulting in seizures can be separated into those causes arising within the
dog itself (endogenous) for example due to liver disease, or those arising external to the dog
(exogenous) such as toxins. There are numerous metabolic diseases that can result in seizures. These
include low blood sugar (hypoglycemia), high blood sugar (hyperglycemia), liver disease,
kidney disease, electrolyte
disturbances, toxins (poisons), anemia, and heart and lung diseases.
Structural diseases which result
in seizures include hydrocephalus, storage diseases, cancer (primary and
secondary brain tumor), inflammatory diseases (infectious and non-infectious
encephalitis), trauma (injury), and blood-vessel-based diseases. Primary brain
cancers originate in the brain whereas secondary cancers develop when
cells from cancers outside the brain are carried to the brain in the
blood.
Idiopathic epilepsy is a seizure
disorder without obvious cause. Idiopathic seizures (Idiopathic epilepsy)
begins between 1 year and 4 years of age. Therefore, a dog that begins having
seizures at 9 years of age does not have idiopathic epilepsy. Certain breeds
of dogs are known or thought to have an increased incidence of idiopathic
epilepsy such as beagles, Belgian Tervurens, German shepherds, keeshonds, and
collies. High incidence breeds include the Saint Bernard, German shepherd,
golden retriever, Irish setter, American cocker spaniel, Wire-haired fox
terriers, Alaskan malamutes, Siberian Huskies, and miniature poodles.
To search for an extracranial cause for seizures, a metabolic evaluation is
performed. The evaluation may include a complete
physical examination, blood tests and sometimes x-rays. To search for a
mass in the brain an imaging study (CT, MRI) is performed and sometimes cerebrospinal
fluid (CSF) is collected. An electrical brain (EEG) evaluation is usually not
very helpful, unless it is necessary to localize the seizure focus.
If an underlying disease can be found, then primary
treatment for that disease may help to make the seizures stop. If the seizures
are recurrent, anticonvulsant medications are often given. The choice of
medication depends upon the characteristics of the individual animal's
problem. Some of the more commonly used anticonvulsants are listed below. It
is important to remember that once an anticonvulsant is initiated, it should
not be changed without veterinary assistance. Most animals
with idiopathic epilepsy will require anticonvulsant medication for the rest
of their life.
Drugs Used to Treat Seizures
- Phenobarbital is a barbiturate.
It is the most commonly used anticonvulsant. Toxicity signs include
drowsiness/sedation, falling, increased drinking, urination and appetite.
With high dosages or prolonged use, phenobarbital can cause damage to the
liver. Paradoxically, some animals given phenobarbital may become restless
and excitable. If this occurs, consult your veterinarian for
assistance. For best results, this drug needs to be given consistently
(every day) at least twice daily. This drug should not be altered without
veterinary consultation
- Primidone is rapidly
metabolized to phenobarbital and some other metabolites by the liver.
Phenobarbital contributes 85% of the anticonvulsant activity due to its
prolonged half-life. It seems to work no better than phenobarbital for most
animals. Acute toxicity signs are similar to those of phenobarbital.
Primidone may be more liver toxic than phenobarbital
- Phenytoin (Dilantin) is a
commonly used anticonvulsant in people. Because it is metabolized
differently in dogs, it not as effective in dogs. It also can be toxic to
the liver. Phenytoin is toxic to cats and should not be used.
- Diazepam (Valium) is a
benzodiazepine. It is a very effective anticonvulsant, but is metabolized
very quickly in dogs, making it's effects short lasting. It is given in
emergency situations because it works quickly. Acute toxicity includes
drowsiness, lethargy, and depression.
- Potassium Bromide is used
mostly as a secondary anticonvulsant in animals refractory to phenobarbital,
however, can be used alone. Due to its lack of metabolism it is the ideal
anticonvulsant for patients with liver disease. Acute toxicity includes
vomiting, anorexia, constipation, sedation and incoordination.
This information was made possible by funds from the
Neurology
Endowment at Washington State University.
Washington State University assumes no liability for injury to
you or your pet incurred by following these descriptions or procedures.
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Last Edited: Dec 20, 2007 11:08 AM
