Epilepsy

Seizures are the result an abnormal nerve impulse boost that comes from the brain, resulting in mild to severe muscular responses. Causes for seizures in dogs and cats include ingestion of toxic substances, electrolyte disturbances, imbalances of metabolism created by underlying disease, or distemper (dogs only). In the case of primary epilepsy, the seizures have no apparent underlying cause, resulting from an abnormal nidus in the brain that fires autonomously. Because primary epilepsy has no apparent underlying cause, it is often called idiopathic epilepsy, “idiopathic” being a term that describes a disease as having no apparent underlying cause. Primary epilepsy is widely believed to be inherited, as evidenced by it prevalence in certain lines of dogs and cats, as well as its tendency to exist more commonly in pure bred animals a opposed to those of mixed breed. Overall, in my experience, primary epilepsy is considerably more common in dogs as it is in cats. Although a seizure is a dynamic process, and seems to come on at times instantaneously, there are 4 distinct phases of a seizure. Whether each phase can be clearly observed, depends on the severity of disease and how fast they come on.

The first stage of a seizure is termed the prodome. This is a period preceding the siezure for any amount of time ranging from seconds to up to several hours. During the prodome a dog or cat’s behavior often changes. Some become exceptionally fearful, some more clingy and needy, while other may even become aggressive.

The aura is the phase that marks the beginning of the actual siezure. The aura is usually evident as increased restlessness, apprehension, trembling, whining, and salivation.

The ictus is the actual seizure where the animal is experiencing full blown convulsive activity. This includes: loss of consciousness and fall to the ground, paddling of the feet, vocalizing, and uncontrollable urination and defecation. The ictus can last anywhere from 30 seconds to several minutes.

The post ictus/ictal is the period immediately following the seizure, when the dog may pace endlessly, appear blind and deaf and eat or drink excessively.

The first step when presented with a seizuring patient is to stop the seizure and prevent further seizure. Always bear in mind that once a seizure has lasted for 5 minutes or longer, the probability of irreversible brain damage increases considerably. That is why it is important that a seizuring dog or cat be seen by a veterinarian immediately. Even if a seizure has come and gone, the pet should still be seen ASAP, as the post ictal period often leaves the patient in a state where it can easily slip back into a seizure.

As mentioned earlier, epilepsy, while it is the most common cause of seizures in dogs and cats, it is one of many different causes for seizures. Therefore, a thorough diagnostic work-up is necessary before assuming a diagnosis of epilepsy. This work-up includes an examination that includes a full neurological assessment, and comprehensive bloodwork and urinalysis. Bloodwork should include CBC (complete blood count), SERUM CHEMISTRY, T4 (thyroid hormone level). If the patient is found to have any underlying diseases that are known to cause seizures, treating such conditions may eliminate seizures. If diagnostics turn up negative for other predisposing disease, then a diagnosis of epilepsy is assumed.

Treatments for epilepsy:

Benign Neglect: Benign neglect means that no treatment will yet be administered. This should only be considered when frequency and duration of seizures are not a major threat, and are not significantly affecting quality of life. Seizures that occur only once a month or less, and have a duration of 1 minute or less, fit the criteria for benign neglect. Owner must be cautioned to monitor the patient carefully, and alert the veterinarian if there are any increases in frequency or duration of seizures. Ideally, an owner should keep a log book of seizure activity for this purpose.

Phenobarbitol: Phenobarbitol is the main anticonvulsant used to suppress seizure activity in dogs and cats. Phenobarbitol has a wide dosing and safety range. The plan is always to begin with a conservative dose if possible, and increase only as is necessary. Phenobarbitol sometimes causes mild to moderate sedation in the first 5-14 days of treatment. However, this passes as the patient becomes refractory to the sedative effects. Regular bloodwork assessing liver enzymes and blood levels of the drug are necessary while on phenobarbitol.

Potassium Bromide: This drug is rarely used as a primary anticonvulsant. Most commonly, potassium bromide is used in dogs as an adjunctive therapy used concurrently with phenobarbitol in cases where phenobarbitol is not effectively controlling seizures and the dose is approaching its maximum level. Potassium bromide is rarely used in cats due to high incidence of adverse side effects in the species. A better choice for cats with epilepsy not adequately responding to phenobarbitol may be Keppra (see below). Like phenobarbitol, patients on potassium bromide should have liver enzymes and drug levels regularly assessed with bloodwork.

Valium (Diazepam): Diazepam is an effective drug for stopping seizures and suppressing the post ictal period when administered intravenously, rectally, or orally in dogs and cats. Onset of anticonvulsant activity is fastest when given orally or rectally. However, given the short duration of activity of diazepam, it is a poor choice for long term treatment of epilepsy

Keppra: Keppra is an excellent long term anticonvulsive treatment that has the added benefit of being associated with an exceptionally low incidence of toxicity. The draw back of Keppra at this time remains its high cost. Therefore, in most cases, Keppra is reserved for use in dogs as an additional anticonvulsant to be used in cases where seizure suppression has become refractory to doses of phenobarbitol and potassium bromide that are approaching the maximum. It also may be a better choice than potassium bromide for additional anticonvulsant therapy for cats in cases where phenobarbitol alone does not adequately control seizures.

In most cases of primary or idiopathic epilepsy, prognosis is favorable with treatment. In cases that are not responsive to conventional treatments, advanced imaging of the brain with CT scan or MRI should be considered to rule out brain tumor. Cerebrospinal fluid tap should also be considered for the possibility of infectious or autimmune encephalitis.

Roger L. Welton, DVM
Founder and Chief Editor, Web-DVM.net
President, Maybeck Animal Hospital

Article updated 10/12/2012