What is Epilepsy?
Epilepsy is a condition in which patients have recurring seizures (also known as epileptic fits or convulsions). A seizure occurs when the brain’s normal neuron function (neurons communicate with each other using tiny electrical discharges) becomes unregulated and chaotic, leading to widespread, unregulated electrical discharges running throughout the brain.
Epilepsy can occur in several ways. Reactive epilepsy occurs when factors external to the brain disrupt the normal workings of the neurons. This can occur with other diseases in the body (such as low blood glucose levels, liver failure) or if your pet has eaten or become exposed to a toxin (such as snail bait or lead). Secondary epilepsy occurs when there is a disease or abnormality within the tissue of the brain itself such as an infection, a blood clot or a tumour. Just about any condition that disrupts the tissue of the brain can disturb neuron functioning and lead to seizures. Primary epilepsy occurs when there is no obvious identifiable abnormality in the brain (as far as we can detect with tests such as MRI, CT scan – even if samples of the brain are taken and put under a microscope). This last type of epilepsy is the type of epilepsy that most people think of when they hear the word ‘epilepsy’ and is often referred to as either idiopathic or cryptogenic epilepsy.
Why do seizures occur?
We are still unsure what the trigger(s) is or are for most seizures and there is evidence for several different (and conflicting) theories. There is evidence for neurons being too excitable because of altered levels of neurotransmitters (the body’s chemicals that regulate neuron communication). There is also evidence that suggests that neurons in the brains of animals with epilepsy are either firing too synchronously or not synchronously enough. In the field of human epilepsy there is an increasing move to label most idiopathic epilepsy as being genetic in nature. Probably this means that very subtle rearrangements of a few genes alters the function of some of the proteins within neurons, leading to slightly different levels of excitability that makes them more likely to fire than the neurons in brains of people without epilepsy. At least that’s the theory. In animals there are small number of breeds in which epilepsy has been shown to be truly genetic (ie the gene that is dysfunctional has been identified, such as in the Lagotto Romanolo) and several breeds in which it is likely to be genetic given the increased incidence of epilepsy in some families in those breeds (eg irish wolfhounds, labradors). However for the majority of dogs and cats with primary epilepsy the underlying cause is unknown.
What do seizures look like?
Since a seizure consists of neurons within the brain discharging randomly and chaotically, the appearance varies depending on which part of the brain is affected. The most common seizure type, the ‘generalised tonic-clonic’ seizure, involves the whole brain. Animals (and people) having this type of seizure lose consciousness, fall over and exhibit running or paddling movements. There may also be chewing, frothing at the mouth and loss of bowel and/or bladder control. It can look pretty distressing and upsetting to watch but most of the time the actual seizure is over within 1-2 minutes. The seizure (or ictus) is often preceded by a ‘pre-ictal’ state, sometimes called the prodrome, or aura. During this phase, the brain is not normal and many animals exhibit behaviours that could be consistent with being fearful or afraid – they may become clingy or anxious and follow their owners around for a variable period of time before the actual seizure. Following the seizure there is also often a ‘post-ictal’ phase where the brain is still not normal but the seizure itself has finished – animals may not be able to see for a period of time, they may run aimlessly or they may display altered behaviour (occasionally this can persist for more than 24 hours but usually this phase resolves within an hour or so).
Seizures may happen at any time of the day or night, although they are more common at night or during sleep, and may occur with a frequency that can vary from twice a year (or less) to multiple times per day.
Not all seizures involve the whole brain. Focal seizures involve only part of the brain and result in uncontrolled movements in one part of the body (eg rhythmic twitching or movements in one limb or just affecting the head/neck). The patient may or may not have altered consciousness and these seizures may either remain focal or may turn into a generalized seizure.
In people, some seizures involve parts of the brain that don’t control movement – vision processing centres or hearing processing centres, for example. As a result, some seizures in people result in auditory or visual hallucinations. In theory, this should also be true in dogs and cats, but it’s difficult to ask a dog or cat what they are experiencing!
Are seizures dangerous?
Provided that seizures stop on their own (as the vast majority do), seizures in themselves are not usually dangerous for dogs and cats. In people seizures are more dangerous because patients may hit their head during the violent, uncontrolled movements, and cause significant brain trauma. Due to anatomic differences (and the fact that dogs and cats are closer to the ground than people) this almost never happens in dogs and cats. People that suffer generalized tonic-clonic seizures report that they have no memory of the event and wake up afterwards feeling fatigued but otherwise without any major side effects. As a result we think the same occurs in dogs and cats, and that they have no major after-effects. This is the case in the vast majority of seizures. However a very small percentage do not terminate on their own and continue – this is known as status epilepticus and can be very dangerous. Status epilepticus can be life-threatening in large part because the ongoing seizure activity results in dangerous elevations in body temperature and other systemic problems secondary to the continuous muscle activity caused by the seizure. For this reason it is important to take you pet to the vet as soon as possible if a seizure doesn’t terminate on its own within 10 minutes.
How do we diagnose epilepsy?
Since seizures and epilepsy are an indication that there is a problem in the brain, the tests that we perform to diagnose epilepsy are designed to diagnose diseases of the brain. Your pet may require a series of blood tests to rule out conditions such as diabetes and liver disease, and possibly tests to look for infections that can affect the brain specifically. Following these tests, your pet may need an MRI (imaging) to look for problems within the brain itself (eg infections in the brain, tumours, blood clots). A CSF tap (also known as a spinal tap or lumbar puncture) may also be performed to look for evidence of inflammation in the brain. If all of these tests are negative, then a diagnosis of primary epilepsy is made. In other words, diagnosing primary (or idiopathic) epilepsy involves excluding all other causes of seizures.
How do we treat epilepsy?
Frustratingly, the options for treating epilepsy in dogs and cats remain limited. When we find an underlying cause in the brain (e.g. tumours or an infection) we try to treat it since this may improve the seizures. However when this is not possible we have to rely on drugs (anticonvulsants). There are several different anticonvulsants, and we may need to trial more than one drug to see which is the most effective for your pet. These include (the common ones):
- Phenobarbitone: one of the oldest anticonvulsants that we have available, and also (still) probably the most effective. Common side effects include: increased thirst and appetite, increased urination frequency, increased appetite, raised liver enzymes and at higher doses, increased sedation and an unsteady hindlimb gait. Rarely it can suppress bone marrow function, and if used at high doses for long periods of time it can cause liver toxicity. For this reason we monitor liver function in patients on phenobarbitone therapy at regular intervals.
- Potassium bromide: Potassium bromide use goes back even further than phenobarbitone (to the 1800s). Chemically it is very similar to salt and its absorption from the gastrointestinal tract is affected by how much salt is in the diet, which means that if your pet is taking potassium bromide it is important that the diet remains unchanged. Common side effects are similar to phenobarbitone’s – increased thirst and hunger, unsteady hindlimb gait (especially at higher doses) and sedation. Potassium bromide is not used in cats since it can cause significant problems with lung function and can even be fatal. It is also important to remember that potassium bromide takes a long time to achieve stable levels in the blood stream – up to 3 months with ordinary daily dosing.
- Imepitoin (Pexion): Imepitoin is the most recent anticonvulsant developed for use in dogs. Its mode of action is similar to phenobarbitone’s but it has less side effects, less effects on liver function and is less sedating than phenobarbitone.
- Levetiracetam (Keppra): Levetiracetam has been available in Australia for approximately 10 years and is very commonly used in the human field. It is very safe and has few side effects other than increased sedation when used in conjunction with other anticonvulsants. We will often restrict its use to patients who are having cluster seizures since it takes effect very rapidly.
- Zonisamide (Zonegran): Another relatively recent drug in Australia – and like levetiracetam this is an anticonvulsant that has few side effects and is safe to use. It only needs to be given twice daily, which makes it more convenient than levetiracetam. However it is one of the more expensive anticonvulsants available.
What happens next?
Living with a pet who has been diagnosed with epilepsy can be challenging. Generally we try to reduce seizure frequency to less than once monthly (or one cluster every 6 weeks). We try to do this with only one anticonvulsant, but frequently we may have to add in a second, or even a third. Approximately 75% of patients with epilepsy will achieve acceptable control but some dogs and cats will continue to have seizures more often than we would like. In the long term (and even if seizures are well controlled) we aim to see your pet at least every 6 months to check on seizure frequency and medication and to take blood samples to check levels of anticonvulsants and other important parameters such as liver enzymes.
Successfully managing epilepsy is a lifelong process that involves a close relationship between you, your vet, and your neurologist. It is very useful to record seizures in a seizure diary – either online (there are some good apps available for smartphones) or paper form. There are likely to be frequent changes of medication and lots of trips to the vet. A big part of our job as neurologists is to ‘hold your hand’ through the process so contact us.
- One of the more useful epilepsy tracking apps is RVC Pet Epilepsy Tracker: https://itunes.apple.com/au/app/rvc-pet-epilepsy-tracker/id992917809?mt=8
- The University of Missouri hosts a very good website that has a lot of information about canine epilepsy: http://www.canine-epilepsy.net/