Focal Seizures and Fly-Biting in Dogs

By Tammy Hunter, DVM; Catherine Barnette, DVM


What are focal seizures?

A seizure is an abnormal surge of electrical activity within the brain. When an animal experiences a seizure, the electrical signals become hyperactive and begin firing abnormally, causing various 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 electrical activity surge confined to a specific area of the brain. Unlike a generalized seizure, in which the animal’s entire brain is affected, and the whole body shows signs of a seizure, a focal seizure only affects a localized region of the brain and only has limited effects on the body. These effects may vary significantly, depending on which portion of the brain is affected.

What is fly-biting?

Fly-biting seizures are a type of focal seizure in which a dog snaps at the air like 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 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 an electroencephalogram (EEG). This test allows a veterinary neurologist to record a dog’s brain waves during an episode to 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’. 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 needed to assess the function of your dog’s liver, kidneys, and other internal organs.

"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."

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 essential to perform this workup to rule out underlying medical conditions. If your dog has an underlying medical cause for fly-biting, treating that condition will be necessary for successfully managing 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 used for generalized seizures can be used in managing focal seizures and fly-biting. Medications commonly used for treating 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 to determine which medication to prescribe.

"Once started on anti-epileptic medications, your dog will likely continue them for the rest of his life."

Once started on anti-epileptic medications, your dog will likely continue them 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 require treatment. With treatment, many dogs 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, significantly impacting the dog’s overall health and quality of life.

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