Focal or Partial Seizures in Dogs
Focal seizures in dogs (sometimes called partial seizures) only affect one half of the brain, and within a particular region of that half. These seizures are described as either simple or complex, depending on your dog’s level of awareness while the seizure is occurring. Dogs usually remain conscious during a simple focal seizure, whereas consciousness is likely to be more impaired if your dog has a complex focal seizure.
Dogs experiencing a simple focal seizure could display one or more of the following signs:
Generalized seizures in dogs occur within both sides of the brain. Generalized seizures often start out as a focal seizure then evolve into a generalized seizure. Dogs experiencing a generalized seizure will usually lose consciousness and may urinate or defecate while unconscious.
Generalized seizures are characterized by movement on both sides of the body and fall into different categories:
In dogs that experience seizures, focal seizures which evolve into generalized seizures are the most common. Often the focal seizure is so short or subtle that the signs are missed by pet parents.
If your dog begins having a generalized seizure, try to remember exactly what they were doing right before the generalized seizure began. Was there an unusual behavior before the seizure began? Provide your vet with a detailed explanation of what happened. The more your vet knows about what your dog was doing before the generalized seizure, the better able they will be to diagnose the type of seizure your dog had and possible cause.
Translational research elements, those that bridge the species gap, can be observed across a broad range of clinical areas. Many of the types of familial epilepsy seen in dogs are similar to those that cause inherited human seizures1,10, and drug research has been shown to be beneficial to both species. Canine epilepsies have also been used as a testing ground for new therapeutic options that can help dogs and humans alike. For example, preliminary research on intracranial electroencephalography (iEEG) in dogs suggests that the technique might be a way to predict seizures, which has the potential to be incredibly helpful for individuals who currently suffer from seemingly random epileptic events4.
Gene mutations have been identified, many of which include a group of diseases known as neuronal ceroid-lipofuscinoses. These are storage disorders where mutations lead to the abnormal accumulation and storage of a cellular product within cells, eventually leading to the dysfunction or death of neurons1. One gene for an inherited epilepsy has been identified in Lagotto Romagnolo dogs. That gene, LGI2, is similar to the previously identified human epilepsy gene LGI1, and scientists believe that a number of heritable epilepsies may have similar causes in humans and canines1. Research into potential similarities between dog and human epilepsies has also led to the identification of several candidate genes that may predict the effectiveness of anti-epileptic treatment in some breeds.
There are limits, of course. Canine epilepsy isn’t identical to human epilepsy, and several drugs have already been shown to have differential toxicity in dogs and humans5,8,10. Additionally, owners have a limited ability to monitor their dogs’ seizures, particularly when compared to how well people can report on their own seizures10. Still, the extent to which naturally occurring epilepsy in dogs is similar to epilepsy in humans presents a unique opportunity to study canine epilepsy as a model to help dogs and their owners alike.
Although classification systems exist for human seizures, there is not yet a widely accepted classification system available for seizures in dogs1. While human systems are sometimes used to describe canine seizures, this can be problematic. Human classifications are not always clearly applicable to canines, and there is often confusion about the meaning of specific terminology in the veterinary setting. This is particularly true of those classification elements which require subjective reporting of symptoms. For example, while dog owners may notice a specific behavior that typically precedes a seizure and is indicative of a behavioral change, there is no direct way to determine the presence of a pre-seizure event as sometimes diagnosed in humans.
It is not always possible to identify the cause of seizures in dogs; however, canine epilepsies can generally be classified into one of three categories based on etiology. Idiopathic epilepsy is defined as epilepsy without an identifiable structural cause and having an assumed genetic origin. Repeated seizures in 1-5 year old dogs with a normal neurologic examination, where there are no known structural abnormalities of the brain, metabolic diseases, or toxin exposures, are often assumed to be a form of idiopathic epilepsy5. The designation of idiopathic epilepsy suggests that the exact cause of the seizures is unknown, although the condition is presumed to be inherited. However, the cause of such epilepsies can sometimes be determined, for example when seizures are the result of a specific genetic defect known to occur in certain breeds.
What are the symptoms of seizures?
There are three stages of a seizure in dogs:
Aura: Minutes before the actual seizure, a period of altered behavior may occur called the aura. This is not always recognizable, but many owners report their dogs may hide, appear anxious, attention seek, or whine just prior to a seizure.
Ictus: The actual seizure is called the ictus. It usually lasts seconds to one to two minutes and is self-limiting, but longer seizures can occur. Seizures can have a variable appearance (as described below).
Postictal phase: After the seizure, many dogs exhibit a postictal phase characterized by disorientation. This may last minutes to hours. The most commonly reported signs are behavior changes, prolonged sleepiness, confusion, transient blindness, and eating voraciously.