Focal Seizures and Fly-Biting in Dogs

What are focal seizures?

A seizure is an abnormal surge of electrical activity within the brain. Electrical signals are consistently passing along and between neurons in the brain, controlling conscious and unconscious thought, movement, and all of the other functions of the brain. When an animal experiences a seizure, these neurons become hyperactive and begin firing abnormally, causing a variety of visible effects on the body. This abnormal activity often arises without any specific trigger, and usually resolves on its own without treatment.

A focal seizure refers to an abnormal surge of electrical activity that is confined to a specific area of the brain. Unlike a generalized seizure, in which the animal’s entire brain is affected and therefore the entire body shows signs of a seizure, a focal seizure only affects a localized region of the brain and therefore only has limited effects on the body. These affects may vary significantly, depending on which portion of the brain is affected.

What is fly-biting?

Fly-biting seizures are a specific type of focal seizure, in which a dog snaps at the air like he is biting at invisible flies. These episodes usually begin without warning, while the dog is resting or relaxed. Some dogs snap casually and intermittently at the air during these episodes, while others become frenzied and possibly aggressive.

During these fly-biting episodes, dogs typically remain aware of their external environment. In many cases, they can even be distracted from these episodes by their owners.

How are fly-biting and focal seizures diagnosed?

The only way to definitively determine that fly-biting and other suspected focal seizures are caused by seizure activity is through the use of an electroencephalogram (EEG). This test allows a veterinary neurologist to record a dog’s brain waves during an episode, in order to accurately determine whether the behavior is caused by abnormal electrical activity within the brain. Unfortunately, fly-biting and other focal seizures often occur intermittently and unpredictably, making this test impractical in most cases.

Therefore, fly-biting and focal seizures are typically a “diagnosis of exclusion.” This means that if your dog’s clinical signs suggest fly-biting or other focal seizures, your veterinarian will perform tests to rule out other causes of these episodes. Screening bloodwork may be performed, to assess the function of your dog’s liver, kidneys, and other internal organs. Your veterinarian may recommend additional testing, such as infectious disease titers, abdominal ultrasound to assess the internal organs, brain imaging (CT scan or MRI), or cerebrospinal fluid analysis. While these tests often come back normal in patients with fly-biting or focal seizures, it is important to perform this workup in order to rule out underlying medical conditions. If your dog does have an underlying medical cause for the fly-biting, treating that condition will be essential for successful management of the episodes.

Once a diagnosis of focal seizures or fly-biting has been suggested, response to treatment can often be used to confirm the diagnosis.

How are focal seizures treated?

The same anti-epileptic medications that are used for generalized seizures can be used in the management of focal seizures and fly-biting. Medications commonly used for the treatment of seizures in dogs include phenobarbital, zonisamide, potassium bromide, and levetiracetam. These medications vary in their benefits and possible side effects, so your veterinarian will consider your dog’s individual history in determining which medication to prescribe.

Once started on anti-epileptic medications, your dog will typically remain on these medications for the rest of his life. Long-term use of anti-epileptic medications requires laboratory monitoring, although the exact requirements for monitoring vary based on the specific drug and patient.  Some medications require only the monitoring of routine screening bloodwork (to assess for side effects), while other medications require the monitoring of blood levels of the drug to ensure that changes in dosage are not needed.

What is the prognosis for focal seizures?

If focal seizures are infrequent, they can often be left untreated. Frequent focal seizures, however, can negatively impact a dog’s quality of life and therefore require treatment. With treatment, many dogs will experience a reduction in the frequency or severity of their focal seizures. It may take trials of several different medications to find an effective treatment

In rare situations, focal seizures (especially those that are frequent or severe) can progress over time to generalized seizures, having more significant impacts on the dog’s overall health and quality of life.