by John Dillberger, DVM
Reprinted from the May/June 2014 issue of The Claymore
Over the past 25 years, many Deerhound owners have contacted me or another SDCA member who is a veterinarian with questions about seizures.
Such concern is understandable. A seizure can be dramatic and frightening to witness in any dog, but even more so in a giant breed like a Deerhound.
Based on the 2011 Deerhound Health Survey, seizures are one of the more important health problems in Deerhounds. Seizures were reported for 11 of 273 males and 12 of 315 bitches, which is 4% of the population. The age at which seizures began ranged from as young as 7 months to as old as 11 years. This wide range isn’t surprising because seizures are not a disease in themselves, but are instead a clinical sign of abnormal brain function. There are literally dozens of different diseases that can affect brain function and cause a seizure, as well as a number of clinical signs that can mimic a seizure.
You can get an idea of some possible causes of seizures by reviewing the comments from the Deerhound Health Survey. For instance, a 2-year-old bitch had “two seizures brought on by over-activity and over-heating.” She lived to be almost 10 years old and never had another seizure. Indeed, hyperthermia can cause seizures.
Another bitch “had three seizures that appeared to be low blood glucose-related. The first occurred at 4½ years old and the last occurred at 5 ½ years old.” It is true that low blood sugar can cause seizures.
A 5½-year-old male “had two seizures about a year apart… I often wondered if it had to do with being hit by a car as a youngster.” As it happens, a head injury can lead to seizures, which may not begin until years later.
A 6-year-old male “had three seizures in 5 days and was diagnosed with idiopathic epilepsy, anaplasmosis, and ehrlichiosis (E. canis). Tried to manage him with doxycycline but no anticonvulsant drug(s), but eventually put him on potassium bromide (KBr) to control seizures. We had to leave him on both the KBr and the doxycycline, though—if we stopped either, he would have a seizure two weeks later. If he were on both, he went as long as 8 months without a seizure.” Each of these infectious diseases can be a cause of seizures in dogs.
Another bitch had her first seizure “about 6 weeks after going into season twice, then more often.” Estrus is not itself a cause of seizures; however, the changes in hormone levels that occur during the estrus cycle can affect the risk of seizures in a bitch.
What is a seizure?
A seizure is a temporary, involuntary disturbance of normal brain function that is characterized by abnormal electrical activity in the brain and usually accompanied by uncontrollable muscle activity. A seizure also may be called a convulsion or a fit. If a dog has repeated seizures and no underlying cause can be identified, then the term epilepsy is used to describe the condition, sometimes preceded by the adjective primary, functional, or idiopathic. Epilepsy is probably the most common cause of seizures in dogs.
The medical term for seizure is ictus. Every seizure has three phases, called the pre-ictal phase, the ictal phase, and the post-ictal phase.
The pre-ictal phase, or aura, precedes the seizure itself and may last from a few seconds to several hours. During the pre-ictal phase, the dog often will behave differently, acting like it senses that something is about to occur. It may hide, appear nervous, or seek out its owner. It may be restless, whine, shake, or salivate.
The ictal phase is the seizure itself, which can last from a few seconds up to five minutes. During a seizure, the dog may lose consciousness or may just have a change in mental awareness (“absence” seizures or hallucinations such as snapping at invisible objects). If the dog experiences a grand mal, or full-blown seizure with loss of consciousness, all of its muscles contract spastically and erratically. The dog usually falls over on its side and paddles its legs while seeming to be otherwise paralyzed. Its head often will be drawn backward, and it may salivate, make chewing movements, urinate, or defecate. If the seizure has not stopped within five minutes, the dog is said to be in status epilepticus or prolonged seizure. Status epilepticus is considered an emergency, and medical help should be sought immediately.
The post-ictal phase is the period after the end of the seizure, during which the dog may appear confused, disoriented, or even blind. The dog may salivate, be restless, or pace. This period can last many hours, there is no relationship between the severity of the seizure and the duration of the post-ictal phase.
What to do if your dog has a seizure
Despite the dramatic and violent appearance of a seizure, people who have seizures report that seizures are not painful, although an affected person may feel confusion or even panic. Presumably the same is true for dogs.
Contrary to popular belief, dogs do not swallow their tongues during a seizure, although they may bite their tongue accidentally. This is important because, if you put your fingers or an object into a dog’s mouth to try to keep it from swallowing its tongue, you will not help the dog and you run a high risk of being bitten very badly or of injuring your dog.
The important thing to do for a seizuring dog is to keep it from falling or hurting itself by knocking objects onto itself. As long as it is on the floor or ground, there is little chance of harm occurring.
A single seizure is rarely dangerous, but multiple seizures within a short period of time (cluster seizures) or a seizure that continues for more than a few minutes (status epilepticus) can cause the body temperature to rise. If the temperature gets too high, then another set of problems may have to be addressed, including secondary brain damage.
Once the seizure is over, and assuming it is the dog’s first, then it is time for a visit to your veterinarian to investigate possible causes.
What to expect from your veterinarian
As I mentioned earlier, a seizure is not a disease in itself but a manifestation of an underlying disease. For this reason, you should expect your veterinarian to take a stepwise approach, first gathering information, then building a list of possible causes, then gathering additional information to rule each possible cause in or out.
The first step is to interview you and get a good medical history about your dog and the seizure itself. Your veterinarian will focus on the following:
- The age at which your dog had its seizure (or its first seizure). This can help narrow the list of possible causes, as different seizure-causing diseases are more likely at different ages. For example, seizures due to a portosystemic shunt tend to occur in young dogs, while seizures due to a brain tumor tend to occur in old dogs.
- Your description of the seizure episode from start to end. This can help confirm that the episode was indeed a seizure and aid in recognizing clinical signs that mimic a seizure, such as fainting, dizziness, muscle weakness, muscle cramping, or a disease of peripheral nerves that doesn’t involve the brain.
- The frequency of seizures, if your dog has had more than one. Not only can this provide information about the possible disease causing the seizures, but it can help you decide whether or not to start treatment with anticonvulsant drugs.
- Any past event that might have damaged the brain and left a scar that could trigger a seizure. For reasons that are not understood, seizures may not begin for years after such brain damage occurs. The event might be a head injury, particularly if it resulted in loss of consciousness—for example, if the dog was hit by a car or kicked by a horse. It might be an episode of hyperthermia. It could be a brief period of time when the brain did not get enough oxygen, such as a difficult birth, or near-drowning, or a prolonged pause in breathing during anesthesia. It might be a past episode of brain inflammation (encephalitis or meningitis) due to an infection or an immune-mediated disease.
- Access to, or possible exposure to, poisons such as prescription medications, illegal drugs, caffeine, chocolate, insecticides, or lead.
- Travel history, since some diseases that can cause seizures are more common or only present in specific regions or parts of the world.
- The occurrence of seizures or a diagnosis of epilepsy in any relatives of your dog.
- The vaccination status of your dog, particularly for canine distemper and rabies.
- Your dog’s diet, and also any particular foods that might have been eaten shortly before the seizure occurred.
- For a bitch, the reproductive status when the seizure occurred. Seizures are more likely in bitches during estrus or pregnancy.
The next step will be a physical examination, looking for any signs of underlying disease that might be present and connected to the seizure. This should include an examination of the eyes with an ophthalmoscope, which can detect increased intracranial pressure or inflammation in the eye that also might involve the brain.
In addition to a routine physical examination, a dog that has seizured should have a special neurological examination. This should be done after the seizure is well past, and not in the post-ictal phase of the seizure.
Laboratory tests also are part of a routine workup for a dog that has seizured. A minimum set of tests generally would be a complete blood count, urinalysis, and serum chemistry profile. The profile should include:
- Liver-related tests, such as enzyme activities (ALT, AST, GGT, and/or alkaline phosphatase), bilirubin, albumin, and a bile acid stimulation test to check for liver disease that might affect brain function (so-called hepatic encephalopathy)
- Kidney-related tests, such as BUN, creatinine, and phosphorus to check for kidney disease that might affect brain function (so-called uremic encephalopathy)
- Glucose to rule out hypoglycemia, which can affect brain function because brain cells need glucose for energy
- Calcium to rule out hypocalcemia, which can affect the function of the brain, peripheral nervous system, and muscles
- Sodium and potassium to rule out electrolyte imbalance. Brain cells require the proper balance of sodium and potassium to function properly.
- If poisoning is suspected, then a blood or urine sample might be taken to analyze for a specific toxin.
- In puppies, a fecal examination for parasites should be done, as a heavy parasite burden can be associated with seizures.
- If hypothyroidism is suspected, then thyroid hormone analysis may be done.
This initial information may indicate the cause of the dog’s seizure, or allow your veterinarian to create a list of possible causes and a plan for ruling them in or out.
It is useful to separate the list into two columns: causes that lie within the skull (intracranial diseases) and those that do not (extracranial diseases).
Extracranial diseases include many of those already mentioned, such as liver or kidney disease, low blood sugar, low blood calcium, electrolyte imbalances, and poisoning. Such a cause might be obvious from the dog’s history and the results of physical and neurological examinations and laboratory tests, or it might require further procedures or tests to establish the cause. For example, if the initial tests suggest that the seizure was due to low blood sugar, then the next step is to discover the cause for the low blood sugar.
Intracranial diseases can be further subdivided into those where some structural problem can be identified in the brain, and those where no abnormal structure is present. Structural problems might be a congenital malformation like hydrocephalus, damage from a past head injury, a tumor in the cranial cavity, or an area of inflammation or infection.
Seizures where neither an extracranial disease nor an intracranial lesion can be identified are grouped into a single category that is given the name “epilepsy,” sometimes modified by the adjective primary, functional, or idiopathic. The term “epilepsy” is used as if it were a single disease, but it is simply a catch-all term for any condition where seizures occur for reasons unknown. Two dogs with epilepsy may have different problems with brain function. Also, it is important to understand that a diagnosis of epilepsy is made by excluding all other causes for a seizure. There is no definitive diagnostic test for epilepsy.
If the disease causing the seizures can be cured, then the seizures should stop. I say “should” because sometimes the seizure itself or the treatment for the underlying disease produces brain damage that then triggers future seizures, even if the cause of the initial seizure is cured.
For example, if the seizures are due to low blood sugar caused by an insulin-producing tumor in the pancreas, then surgical removal of the tumor should stop the seizures. On the other hand, a dog having seizures because of a brain tumor may not be a candidate for surgery, and even if the brain tumor is treated by radiation or surgery, the resulting scar in the brain may itself trigger seizures.
If the disease causing the seizures is epilepsy, then there is no cure. Dogs with infrequent epileptic seizures may not need to be treated at all. On the other hand, if the seizures are frequent, or become so over time, then treatment with anticonvulsant drugs is appropriate. The aim of these drugs is to “control” the seizures (reduce their frequency or severity) with “acceptable” side effects. Consequently, an important part of the decision to start treatment is the judgment that the seizures are frequent enough to justify some side effects.
Antiepileptic drugs can be classified into three broad mechanistic categories:
1) Drugs that enhance inhibitory processes in the brain, usually by augmenting the action of the neurotransmitter gamma amino-butyric acid;
2) Drugs that reduce excitatory processes in the brain; and
3) Drugs that change the efficiency with which individual brain cells transmit a signal.
Unfortunately, many drugs useful in people cannot be used in dogs because they are too quickly cleared from the blood or because of potential hepatotoxicity. Thus, the anticonvulsant drugs most commonly used in dogs are all from the first category.
The initial approach for treating any dog with epilepsy is to use a single anticonvulsant drug, which reduces the chance of harmful side effects from a drug-drug interaction. The current drugs of choice are phenobarbital or potassium bromide (KBr), although newer drugs like felbamate and gabapentin sometimes are used. Phenobarbital is often used in the form of a prodrug called primidone.
The plan for managing a dog with epilepsy should include not only choosing an appropriate drug, but also understanding how to monitor the dog for side effects and that it may be necessary to adjust the dosage or switch drugs from time to time. Owners also should be aware that emergency treatment may be necessary if recurrent or severe seizures occur. This emergency treatment may be given by an owner at home; for example, by administering diazepam (Valium) by suppository to stop a dog having repetitive seizures or in status epilepticus.
A large collaborative study, called the Canine Epilepsy Project, is now underway into the genetic risk factors for epilepsy in dogs. It is jointly directed by Dr. Gary Johnson at the University of Missouri and Dr. Ned Patterson at the University of Minnesota and is supported by grants from the AKC Canine Health Foundation, National Institutes of Health (NIH), individual breed clubs and private donations. As of October 31, 2013, samples from 10,482 dogs representing 122 different breeds had been submitted, including 1,861 samples from dogs with epilepsy. Samples are in hand from a few extended family groups that contain at least 20 “sib pairs” (an affected dog paired with its normal sibling), and some of these have been included in genetic mapping experiments. Although a few genes have been discovered in a few breeds for specific rare diseases that include seizures as one of many clinical signs, at present no gene for epilepsy has been identified in any breed.
For more information, see this earlier post on seizures in Deerhounds.