DOG HEALTH Care Information – Epilepsy in the Dog

What is Epilepsy?

Epilepsy is a disease characterised by the occurrence of fits, or seizures. Epilepsy has many different causes, but what most people think of as “epilepsy” is referred to by vets as idiopathic epilepsy. “Idiopathic” means that there is no identifiable cause. Of course, this does not mean there is no cause, just that it cannot be identified. This article deals mainly with the discussion of idiopathic epilepsy. This is because, if a definitive cause of the seizures is found, then the treatment of the seizures becomes the treatment of the underlying condition, which is more important than treating the seizures per se.

The following breeds are known to be predisposed to idiopathic epilepsy. (Predisposed means a dog of this breed is more likely to become epileptic than the general canine population).

• Alaskan Malamute
• German Shepherd
• Shetland Sheepdog
• Beagle
• Golden Retriever
• Siberian Husky
• Belgian Shepherd (Tervueren)
• Irish Setter
• Springer Spaniel
• Border Collie
• Keeshond
• St. Bernard
• Boxer
• Labrador
• Welsh Corgi
• Cocker Spaniel
• Poodle
• Wirehaired Fox Terrier
• Dachshund
• Rough Collie

What Causes Epilepsy?

We can divide the causes of epilepsy into two main groups:

1. Diseases originating outside the head (extracranial).
2. Diseases originating within the head (intracranial).

Extracranial Causes

There are many diseases which can cause seizures. They include:

• Liver Disease
• Kidney Disease
• Heart Disease
• Poisoning – lead, organophosphates, chocolate and many others
• Hypoglycaemia (low blood sugar)
• Eclampsia (low blood calcium)
• Hyperkalaemia (raised blood potassium)

This is by no means a complete list, and there are an almost limitless number of poisons that can cause seizures. These will not be discussed here.

Intracranial Causes

Again, there are a large number of these, the more common ones being:

Head trauma

Brain tumour

Meningitis

Distemper

Rabies

Brain haemorrhage

The most common type of epilepsy though, is idiopathic epilepsy. Before we proceed down the road of treatment, we need to make some assessment of the dog to see if there is an identifiable, underlying disease, the seizures being one of the symptoms of this disease.

Investigation of Epilepsy.

Many of the diseases listed above are so obvious that little needs to be done in the way of laboratory tests to rule them out. In addition, there are so many different possible poisons, it would be ridiculous to try and test for them all. Fortunately however, poisoning is usually very dramatic, the dog beginning seizures suddenly, followed by a recovery; or progressing to a state where the seizure does not end, or the dog has only a few minutes between seizures. This is known as status epilepticus, and is a serious life-threatening event. The one notable exception to this is lead poisoning, which can result in seizures of a gradually increasing frequency, as the dog consumes small quantities of lead over a long period of time. Diseases like distemper, rabies and meningitis also nearly always have symptoms other than seizures.

The dog with idiopathic epilepsy usually presents having had only one seizure, which lasted a few minutes at most. By the time the dog is examined by a veterinary surgeon, he has usually completely returned to normal. The diseases which are most likely to mimic idiopathic epilepsy are generally hormone driven, and include problems in maintaining normal calcium, potassium, or glucose levels.

Heart disease, kidney or liver disease only rarely cause seizures, but are relatively easily diagnosed. Bearing this in mind, when a dog has its first seizure, and especially in the absence of any other symptoms, we like to perform a blood test to check for these conditions. It is generally not advisable to just wait and see if any more seizures occur.

If the dog’s routine blood test is normal, and in the absence of any other symptoms, idiopathic epilepsy is very likely, particularly in young dogs. In older dogs, some other underlying condition which does not show up on the blood test is very possible.

What to do if Your Dog has a Seizure

If your dog has a seizure, you should usually stand back and let it happen. Don’t try and talk to the dog, or put your head or fingers near its face because you may get bitten. If the dog is at the top of a flight of stairs, in front of an open fire, or in any other location where he may be able to injure himself, then you should try and gently move him to a safer place, but keep away from the head. This is very important, no matter what the dog’s temperament is under normal circumstances.

Try and stay calm. Look at the time and write it down. That way you will be able to tell exactly how long the seizure lasted when it’s over. If the dog comes round within a few minutes, there is no need to panic. Bring the dog along to the next available appointment. If the seizure lasts 20 minutes or more, call the vet on the phone, and seek emergency treatment. This is a genuine emergency, but only if it goes on for more than 20 minutes.

In most cases there will be a period of time after the seizure when the dog appears disorientated. He may wander around aimlessly, appear hungry or thirsty. This is no cause for alarm. Most dogs return to normal within an hour or so. If this period is very prolonged, several hours or even days, it is a good clue that the dog has a physical abnormality within his head, such as a tumour.

Treatment of Epilepsy

Epilepsy is treated with one or more drugs known as anticonvulsants; but there are some occasions where surgery is possible. Male dogs are more likely to become epileptic than female ones, and this is directly the result of male hormones. Castration reduces the incidence of epilepsy, and so epileptic male dogs ought to be neutered. In some female dogs, seizures occur in clusters around the time of their “season” and so spaying is of value in this event.

When to Treat Epilepsy

If the seizures are occurring less than once every three months, then treatment may not be necessary. However, when a dog has just had its first seizure, we have no way of telling when the next one will arrive. There is also evidence that suggests that treatment is more successful the earlier in the course of the condition that it is begun.

Bearing this in mind, at Vetrica we prefer to start treatment after the first seizure. Treatment is generally very safe and inexpensive; if the dog does not have any further seizures over a period of six months to a year, therapy can be cautiously withdrawn.

Aim of Epilepsy Treatment

The aim of therapy is not necessarily to stop the dog having any more seizures, as this is not very likely. In most cases, simply doubling the time between seizures would be considered successful treatment. Anything better than this is a bonus.

Drugs Used to Treat Epilepsy

Before we consider what drugs are available to treat epilepsy in the dog, it is very important to remember the following when using any anticonvulsant:

Never, under any circumstances, stop administering the drug without first reducing the dose very gradually over many weeks or months. A severe exacerbation of the seizures is likely, which may be totally resistant to further treatment.This warning also applies when changing from one drug to another. The original drug must be gradually tapered off, while the new one is gradually introduced.

Phenobarbitone

Phenobarbitone, (Epiphen®), is the drug of choice in all cases of idiopathic epilepsy. It is the cheapest, safest, and most effective of all the drugs licensed for the treatment of epilepsy in the dog in the UK. Phenobarbitone works by suppressing the abnormal electrical activity that occurs in the brain during a seizure. It takes up to two weeks from the start of treatment for the drug to reach stable levels in the blood stream. This means that for the full effect of the drug, you need to wait two weeks. This also applies if the dose is adjusted; two weeks have to elapse to see what the full effect is. Phenobarbitone causes the liver to make more of the enzymes which are used to eliminate it from the body. The consequence of this is that over time, the dog may become tolerant to the drug, and require an increased dose.

The major side effect of phenobarbitone is increased thirst and appetite. Early in the course of treatment, sedation is very common, but in most cases this disappears with continued use of the drug. Ataxia (where the dog is unable to move it’s legs in a normal walking motion) can occur, but again, this tends to diminish with time. Liver damage is possible with phenobarbitone, but usually with prolonged use at very high doses. Blood tests for liver damage should be taken at least once a year when a dog is taking phenobarbitone. If any problems show up on these tests, a lower dose of the drug, an alternative drug, or more frequent monitoring may be required.

After two weeks of phenobarbitone use, the dog should have a blood test to determine the level of the drug in his bloodstream. This is very important, because it tells us whether or not the dose being administered is likely to control seizures, even if there have been none during the early treatment period. It also ensures that there is not an excess of the drug present, which could be very damaging to the dog.

Primidone

Primidone (Mysoline®), is a drug which when administered to the dog, is metabolised (changed) by the liver to other chemicals. The majority of the effect of primidone is due to the production of phenobarbitone from it in the liver. This is considerably more expensive than administering phenobarbitone, and a dog which has not responded favourably to treatment with phenobarbitone is unlikely to benefit from changing to primidone.

All the side effects of phenobarbitone also occur with primidone. However, the incidence of liver damage is much greater than when using phenobarbitone, and blood tests for liver damage should be taken at least every 6 months. There is little point in using primidone in preference to phenobarbitone, and this drug is not in routine use at Vetrica.

Potassium Bromide

Potassium bromide is a drug that may be used as a supplement to phenobarbitone where seizures are not being adequately controlled. It’s generally not effective enough to control seizures on its own, although it is particularly useful when there is evidence of liver disease that would preclude treatment with phenobarbitone, primidone or phenytoin.

Common side effects of bromide are sedation and ataxia. It can also cause vomiting, constipation, loss of appetite, and an increase in thirst. With long term use of high doses pancreatitis has been seen. The pancreas is a gland which produces the enzymes required to digest food, and pancreatitis is a life threatening disease where the gland starts to digest itself. This is thankfully very rare. Regular blood tests to determine the quantity of the drug in the blood are required to ensure that safe levels are being maintained. Salt intake can dramatically affect the amount of bromide present in a dog’s system. For this reason, salty snacks and any sudden diet change should be avoided by dogs taking potassium bromide.

Phenytoin

Phenytoin (Epanutin®), works by suppressing the spread of abnormal electrical activity within the brain. Phenytoin was withdrawn from the UK veterinary market in the late 1990s. This is not a very useful anticonvulsant drug in the dog, because it is very rapidly removed from the body by the liver. This means that high doses need to be given at very frequent intervals. It can however be used in combination with phenobarbitone, if it alone is not controlling the seizures satisfactorily. Phenytoin is not in routine use at Vetrica.

As with phenobarbitone and primidone, ataxia is the most common and liver failure the most dangerous of the side effects. Vomiting is quite common, but can be reduced if administered with food. Peripheral neuropathy, (a disorder of the nerves supplying the limbs), can also occur. There are a few other rare, complicated disorders of the skin and joints also that will not be discussed here.

Benzodiazepines

Benzodiazepines are used in humans as antidepressants, as well as antiepileptics. Benzodiazepines in occasional use at Vetrica are:

• Diazepam (Valium®)
• Clonazepam (Rivotril®)

Like phenytoin, these drugs are too rapidly eliminated from the body to be of much use in the dog. Diazepam is a very useful drug in the emergency situation, as it can be given intravenously or rectally to stop a seizure while it is actually happening. Clonazepam, while unsuitable for use on its own, can be used as a supplement to phenobarbitone. Unfortunately, while clonazepam is a very useful drug, tolerance to its effects can develop, requiring a change to another drug.

What to do if Treatment Fails

Phenobarbitone is the drug of choice for the treatment of canine epilepsy. Only if this drug fails to adequately control the seizures do we use any other drug. First of all though we should define what is meant by treatment failure. If the seizures are reduced in frequency to less than 1 every 3 months, treatment is successful. If the time between seizures has doubled from the pre-treatment level, treatment is successful. Additional treatments may well help in the case of very frequent seizures.

Some dogs have clusters of seizures, a cluster being a number of seizures that occur within a few days of each other, followed by a long period of time until the next cluster. When this happens, there is a real risk of status epilepticus developing. Status epilepticus is effectively one seizure after another with a very short, or absent period of time between seizures. This is very dangerous, and as brain damage can occur, the dog must be taken to the vet immediately. For this reason, dogs experiencing clusters may require additional drugs for a short time. At Vetrica, the most commonly used drugs for this purpose are the benzodiazepenes, diazepam and clonazepam.

If phenobarbitone is not controlling the seizures adequately, we use the following protocol:

1. First, blood test to check phenobarbitone levels in the blood. If there is an inadequate amount of the drug in the dog’s system, or if it is near the bottom end of the range then increase the dose, and re-assess, including another blood test 2 weeks later.
2. Second, if there is sufficient phenobarbitone in the blood, give another drug in addition to phenobarbitone. The combination of phenobarbitone and potassium bromide will adequately control the overwhelming majority of epileptic dogs. However, every dog, is different, and different drug combinations need to be tried in individual cases.

Outlook for Affected Dogs

The vast majority of epileptic dogs live perfectly normal lives, having only infrequent seizures. Once you have come to terms with the seizures, and accepted that they will occur, at least occasionally, no matter what the treatment, life can return to normal. There is however a small proportion of dogs whose seizures are not controlled well with medication. Most of these are dogs which became epileptic later in life, and have some sort of identifiable cause. Unfortunately, euthanasia may be the only option, especially if the seizures are sufficiently frequent, or the underlying cause is untreatable.