Epileptic seizures are defined as transient signs due abnormal excessive or synchronous neuronal activity in the brain, and epilepsy refers to at least two unprovoked seizures more than 24 hours apart. The term idiopathic means a disease of unknown cause. We now better understand that idiopathic epilepsy in dogs most likely has an underlying genetic cause. In spite of this strong evidence for a genetic cause, the association of specific genetic variants with epilepsy in most breeds has remained elusive. The prevalence of epilepsy is significantly greater in purebred dogs versus mixed breed dogs. Male dogs are more commonly affected than females. The majority of epileptic dogs have their first seizure between 1 and 5 years of age, and dogs in that age range are more likely to be diagnosed as idiopathic epileptics, although about one-third of dogs 1-5 years old will be diagnosed with a structural or metabolic cause.
Seizures in dogs with epilepsy can be either generalized or focal in onset. A generalized seizure consists of tonic (stiffening) and clonic (paddling) types of movement and the animal loses consciousness. A focal seizure may consist of abnormal movements in one part of the body with or without a change in consciousness. Importantly, a dog with epilepsy is neurologically normal in between the seizure episodes. The severity of seizures may worsen over time. Sometimes the seizures may last for more than five minutes (status) or occur one after another within a short time period (cluster). Both situations require immediate management by a primary care veterinarian.
Idiopathic epilepsy is diagnosed by ruling out other acquired diseases that also can manifest seizures. A minimum database that includes a complete blood count, biochemical analysis and urinalysis is useful to exclude other underlying systemic diseases outside of the brain. These diagnostic testing procedures also assist in ensuring the animal is healthy for anesthesia. Magnetic resonance imaging is the preferred imaging technique for presumptive diagnosis of epilepsy by ruling out other diseases that are identified by structural lesions such as inflammation or a brain tumor. Analysis of cerebrospinal fluid can aid in diagnosis and ruling out inflammatory disease.
The decision to start antiepileptic drug treatment is based on a number of factors, including the cause of the seizures, risk of recurrence, seizure type and side effects of the medication. A clinician’s decision to start therapy relies on the risk versus benefit and the individualized patient assessment while considering the owner’s financial and emotional commitments. In dogs, long-term seizure management is most successful if therapy is initiated early after onset of seizures, especially in dogs with frequent seizures and in dog breeds known to have severe epilepsy.
Although a variety of drugs are used for management of epileptic dogs, there are no evidence-based guidelines regarding the choice of a first-line drug for long-term management of seizure control in dogs. In principle, administration of a single drug is preferred because it avoids drug interactions and it is more convenient for the owner. Phenobarbital and potassium bromide have been used as first-choice sole drugs for long-term treatment of epilepsy in dogs based on their long-standing history, widespread availability and low cost. During the past 20 years, many newer antiepileptic drugs with fewer side effects and drug interactions have been developed for treatment of human epilepsy. Many of these same drugs have been determined to be safe also in our veterinary patients, such as levetiracetam, zonisamide, gabapentin and pregabalin.
After initiation of a therapy, it is important to systematically monitor the seizure control, systemic effects of the drug, and drug concentrations in the blood. The focus of monitoring treatment is to optimize seizure control while minimizing adverse effects. Epilepsy management depends on accurate owner observation when assessing the efficacy of therapy. Owners should maintain a log to document seizure occurrences and changes in medication administration. Adjustments in dosage often are based on the assessment of the seizure control in addition to blood drug concentration and drug side effects. It is important to have regular assessment of blood concentrations even at times when seizures are well controlled in order to monitor for toxic levels, especially for drugs with a greater potential for side effects (i.e. phenobarbital and potassium bromide), to monitor for blood concentration fluctuations, and to have awareness when there is a need to make changes in therapy.
About 60-70 percent of epileptic dogs achieve good seizure control when their therapy is carefully monitored. Dogs that are not well controlled risk euthanasia due to poor quality of life for the dog and their owners. Risk factors for euthanasia include younger age of onset, high initial seizure frequency, poor seizure control, and episodes of status epilepticus, or seizures that last longer than five minutes. Approximately 40-60 percent of dogs with epilepsy have one or more episodes of cluster seizures or status epilepsy, and a mean lifespan of only 8 years, compared to 11 years for those with epilepsy without episodes status epilepsy. Epileptic dogs that have had cluster seizures are known to be significantly less likely to achieve remission with any treatment. Though life expectancy of the pet may not be affected, the odds of an epileptic going into complete remission and not requiring ongoing therapy are low: 6-8 percent in dogs. Thus dogs with epilepsy usually require lifelong therapy and commitment from the pet owner. A balance between quality of life and therapeutic success is often key for an owner’s commitment to their pet’s therapy.