Seizures, the most common neurologic disorder diagnosed in dogs,¹ are characteristic of epilepsy, which is defined as recurrent seizures over a period of time.² Seizures are clinical manifestations of excess and hypersynchronous electrical activity in the cerebral cortex. The multiple causes of epilepsy include brain tumors, degenerative brain disease, and other brain disorders. Epilepsy affects up to 0.75% of the canine population.³

The most common type of epilepsy is idiopathic, or primary, epilepsy. In idiopathic epilepsy (IE), the underlying cause of recurrent seizures is unknown or no identifiable brain disease can be found.²  

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Certain breeds are predisposed to IE, which, based on epidemiologic studies, is thought to have a genetic basis.⁴

Most IE patients have their first seizure between 1 and 5 years of age, but patients can be older or younger at onset. In one study, 75% of dogs with recurrent seizures at less than 1 year of age (ie, juvenile epilepsy) had no identifiable brain disease.¹ Another study found no apparent cause for seizures in 35% of dogs with seizure onset at more than 5 years of age (ie, late-onset epilepsy).¹ 

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Seizures are described as generalized or focal. Generalized seizures reflect involvement of both hemispheres of the cerebral cortex, whereas focal seizures indicate abnormal activity in one part of a cerebral hemisphere.⁴ Most IE patients display generalized tonic-clonic seizures. During the tonic phase, the patient loses consciousness and falls to one side in opisthotonus with every limb rigid and extended. The clonic phase that follows consists of limb paddling/jerking and chewing movements.¹ Seizures typically have 4 stages: prodrome, preictal, ictus, and postictal.⁵ (See Table 1.)

IE is diagnosed by ruling out all other possible causes of seizures by having a normal neurologic examination, normal lab tests (eg, CBC, serum chemistry, bile acids, thyroid function), a normal brain MRI, and normal spinal fluid analysis. 

Treatment is specific to the patient and based on the veterinarian’s familiarity with and access to antiepileptic drugs (AEDs). A recent consensus statement recommends beginning AED therapy⁶:

• When the patient has more than 2 seizures every 6 months
• When cluster seizures are present
• After any episode of status epilepticus
• When the postictal period is prolonged or unusual

The goal of AED therapy is to significantly decrease seizure frequency and severity while minimizing medication side effects. A drug that decreases seizure frequency by at least 50% is considered efficacious. Treatment may include first-line AEDs only or first-line AEDs in conjunction with other anticonvulsant drugs. (See Table 2.)

If seizure frequency is unacceptable (ie, >1 per month), additional treatment options are limited to increasing current medication dosages or adding a different AED. Nonmedical therapies (eg, diet changes, acupuncture, vagal nerve stimulators) have also been investigated.¹ While the author does not discourage any strategy to help improve seizure control, these ancillary measures have not been studied extensively, making it difficult to advise a patient’s owner on their efficacy. Clients can be instructed to provide supportive care by remaining calm when seizures are occurring to limit injury to the patient and by creating a quiet, dimly lit environment for the recovery.

IE is not curable, and management requires a long-term commitment from the patient’s owner. Approximately 25% of patients with IE will be refractory to one or more anticonvulsant medications.⁵ Comorbidities (eg, anxiety, hyperactivity, behavior changes, medication side effects) contribute to a patient’s decreased quality of life. Dogs with epilepsy have been reported to have shorter lifespans because, as a result of emotional stress to pet owners, treatment cost, and/or patient quality-of-life concerns, many clients choose euthanasia over long-term treatment.⁷