By Dr. Brookshire
Director of Veterinary Services
Epilepsy is a term that simply means seizure disorder. We often make a diagnosis of epilepsy when we cannot identify a cause for the seizures. Another term for this is idiopathic epilepsy. This article will discuss some of the causes of seizure disorders, diagnostic tests that are important, and treatment methods.
Seizures are a scary event. They occur when the normal inhibition/excitation balance that exists within the brain is disrupted. Nerve impulses fire randomly throughout the brain, in an excess of excitatory impulses. This is the typical grand mal, or tonic clonic seizure. Seizures are always preceded by a change in mental status. This change is called an aura. Service dogs are able to recognize this aura period in humans that suffer from seizure disorders, but most people don't recognize the subtle changes in their pet. Following the aura is the seizure, which usually lasts less than 2 minutes, but often seems much longer. Once the seizure activity has ceased, a post-ictal period ensues. The pet may be lethargic and less interactive than normal. This can last from minutes to hours. Grand mal seizures involve complete loss of awareness, lateral recumbency, paddling, vocalization, and often loss of bladder and bowel control. This is not painful, but is very scary to watch. Petit mal seizures are not as severe, and may not even be recognized as a seizure.
In young animals, less than 1 year of age, there are some causes of seizures that we don't usually consider for adult animals. These include: portosystemic shunts, hypoglycemia, and infections (such as Distemper). Portosystemic shunts in young animals are a congenital defect (defect the animal is born with). The main blood flow from the gastrointestinal tract through the liver (where toxins are removed) is diverted around the liver. Blood filled with by-products of metabolism is allowed to circulate through the body. A build-up of a particular by-product called ammonia will lead to abnormal mental status and seizures. Hypoglycemia, or low blood sugar, is most common in toy breed puppies. At a very young age, with excitement or play, the body of these tiny puppies may not be able to draw on reserves of glucose to supply energy. The blood sugar becomes lower and if the animal doesn't get to eat right away, seizure activity can occur.
In adult animals, between 1 and 3 years of age, epilepsy is most commonly diagnosed as “idiopathic epilepsy”. This simply implies a seizure disorder of unknown cause. Idiopathic epilepsy is currently being investigated as a genetic disease. Researchers are working together to identify the gene that is responsible for the condition.
In the overall adult group, between ages 1 and 6 years, idiopathic epilepsy is diagnosed in 2/3 of the cases. In the other 1/3, a cause can be found. Ingestion of a toxin, metabolic disorders, endocrine disease or even traumatic injury can cause seizures. Lead poisoning is the most common toxic cause of seizure activity. Low blood calcium (such as in a lactating mother) can cause seizure activity if not diagnosed and treated. Endocrine disease, such as hypothyroidism, can cause seizure activity. If untreated, too much or too little thyroid hormone circulating in the blood can predispose the animal to stroke, which then leads to seizure activity. Trauma to the head or neck can lead to seizures because of injury to the brain itself or swelling of the brain or spinal cord.
In senior animals, brain tumors are the number one cause of seizure disorders, followed by metabolic disorders. Kidney or liver failure can lead to seizures because of the build-up of toxic by-products within the blood.
When a seizure occurs in a very young animal, in a lactating mother, or lasts longer than 5 minutes, it is an emergency. Otherwise, a veterinary examination can typically wait until the following day. A one-time seizure may not warrant a complete veterinary workup, depending on the situation. However, if a pet has had more than one seizure, a full workup is indicated. This workup includes a complete history (make sure you keep good records of the seizure activity), a physical examination, a neurologic examination, a CBC (complete blood count), a serum chemistry profile, a thyroid hormone level, a bile acids test, and a urinalysis. If all these tests have normal results, further tests may be indicated. These may include a CSF tap (spinal tap), a MRI or CT scan, or even an EEG (a test that graphs the electrical activity of the brain). Often, after the first round of testing, we make a diagnosis of idiopathic epilepsy and move on to treatment.
Treatment is not necessary following one or even two seizures. However, if the seizures are occurring as frequently as every 6 to 8 weeks, treatment is indicated. Why wouldn't we treat after the first seizure? The answer is pretty simple. A seizure may be a one-time event. If we rule out the causes of a seizure and believe that idiopathic epilepsy is the appropriate diagnosis, we should wait until another seizure occurs. This may happen in a day, week, month, or even a year. The medications that we use to treat epilepsy have the adverse side effect of sedation. While most animals get used to this sedation with some time, they are still more lethargic than they were prior to the treatment. Also, long term use of the most commonly prescribed anti-seizure medication, phenobarbital, can lead to liver damage. So, we want to keep the seizures at an acceptable occurrence rate while using the lowest dosage of the medication possible. Blood tests are necessary to ensure that the liver is not being damaged and that the phenobarbital is at a therapeutic, and not toxic level. These blood tests need to be done on a regular basis, and the cost can add up. Often, after treating an epileptic for some time with phenobarbital, we find the need to add other medications. This can be because we see evidence of liver damage on blood profiles, or because we cannot increase the phenobarbital (because of the potential toxicity) and the animal is still having seizures frequently. The medication that we typically add into the mix is called potassium bromide. This medication works well in dogs as an antiepileptic, but can have adverse psychological effects in people, meaning that it should be handled with care. Newer medications are currently being investigated, but are not available for widespread use. These medications are most commonly prescribed by veterinary neurologists when control is not achieved with traditional protocols. In cats, we often start with phenobarbital (same potential side effects as in dogs) and add valium (diazepam) in if we don't achieve adequate control. Potassium bromide can also be used in cats. Monitoring of bromide levels is necessary if this medication is used to treat the seizures.
Alternative therapies are being used in many chronic conditions for humans and for our pets. In the case of epilepsy, acupuncture, massage, and natural diet are 3 things that may help, but certainly do no harm. Food allergy is something that typically causes skin reactions or gastrointestinal upset, but may play a role in seizures. Sometimes an elimination or homemade diet is prescribed to see if it just might help. Unfortunately, it is very difficult to determine response to therapy with some of these alternative therapies. Seizures are very unpredictable and may come as frequently as once a week for several weeks and then stay away for 6 months or more. So, if a treatment is started and no seizures occur for 4 months, it's difficult to say if it's a result of the new treatment or just because. Herbal therapies should probably only be used following a prescription by a veterinary homeopath. Without proper knowledge, many herbs can have potential side effects that may worsen the existing condition.
The Canine Epilepsy Project is a collaborative effort between the University of Missouri – Columbia, the University of Minnesota, The Ohio State University, and the Animal Health Trust. Scientists at these locations are investigating epilepsy and its genetic basis to identify the gene that causes the problem. This can lead to testing for epilepsy prior to the first seizure and removal of affected animals from breeding. Also, eventually it may lead to gene therapy to treat this disease. For more information about canine epilepsy, click here.