Chinook "Seizures"Dennis O'Brien, DVM, PhD
ACVIM, Specialty of Neurology
University of Missouri, College of Veterinary Medicine
Chinooks can have episodes that fall in the gray zone
between seizures and other disorders.
Click on the picture to see a video clip (avi format) of the
episode. It's a big file (10 mb) so it may not run on all home systems
or if you prefer a Quicktime mov file click HERE (650 kb).As part of the Canine Epilepsy Project, we have been investigating reports of "seizures" in Chinooks. This article will share what we know thus far about this condition in this breed.
What do the Chinook "seizures" look like?
A brief video clip of a typical Chinook "seizure" can be viewed by clicking on the picture. In contrast to classic epileptic seizures, the videos show that the dogs appear to be conscious during the episodes and can make some voluntary movements. You will notice the dog in this tape appears to be trying to move toward the owner taking the video and watches the person walking by. While some of the dogs have remained standing and simply freeze in their tracts, most fall or lay to their side. Many tend to curl toward one side. A single limb or several limbs may be pulled up against the body. Sometimes the limb(s) make slow movements, but we have seen none of the violent jerking and paddling movements typical of seizures in the videotapes sent to us. The dogs may tremble or perform licking movements. Some owners report these episodes last for up to 30 minutes or more, although some episodes are brief like classic seizures. Following a classic seizure, the dog is usually disoriented for a variable period of time, while the Chinooks appears perfectly normal afterwards. Some owners have reported specific foods or events which appear to trigger the events, while others seem random.What is the difference between a seizure and paroxysmal dyskinesia?
There is a reason why "seizures" is in quotations in the title. A classic generalized seizure is pretty easy to recognize. The dog loses consciousness, stiffens, falls to their side, and then begins violent paddling or jerking movements. While they may seem to go on forever, a classic seizure lasts less than 2 minutes. Following the seizure, the dog may be disoriented for a period of time, but eventually gets back to normal. If the seizures occur repeatedly over time, then we can say the dog has epilepsy. Some of the variations on the epilepsy theme are also fairly straight forward. Some dogs, however, have episodes that are not as easy to classify. They may fail to lose consciousness, or only one part of the body may be affected. Some of these are focal seizures, while other are more properly classified as movement disorders. Still others may be simply muscle spasms or fainting spell, but since the dog cannot tell us what they feel, all we can do is look at the episode and the results of our tests, and try to classify it as best we can.
Seizures arise from cerebral cortex
(red in this cross section of a brain)
while movement disorders arise from
the basal nuclei (yellow).
The movement disorder in humans that fits into this gray zone is called paroxysmal dyskinesia. Paroxysmal means that there are brief attacks of the symptoms with the dog appearing perfectly normal between the episodes, the same way there are discrete attacks of seizures in epilepsy. Dyskinesia refers to an abnormal, involuntary movement or posture (dys- bad + -kinesis movement). While seizures originate from the cerebral cortex (the wrinkly surface of the brain), movement disorders like the dyskinesias usually originate from the deeper areas (the basal nuclei). These deeper areas have the job of translating the commands from higher brain areas (e.g. get the ball) into movements (e.g. stand up, begin trotting, etc.). Because most human movement disorders, such as Parkinson's disease or Huntington's chorea, are constant, it can be hard to tell simply by watching the episodes whether they are seizures or paroxysmal dyskinesias.
In human patients, the distinction between a true seizure disorder and paroxysmal dyskinesias is based on looking for abnormal electrical activity on the surface of the brain with an electroencephalogram (EEG). By definition, seizures have abnormal EEG activity, while the paroxysmal dyskinesias do not. Recording EEGs in dogs can be challenging, however, and we often have to rely on the appearance of the episodes. Since these are discrete episodes, it is unusual for the veterinarian to even see one of the episodes, but our understanding of these conditions has been vastly improved by the availability of videotape recorders that allow the owners to catch these events on tape so that we can actually see what is going on during them. The episodes we have seen on videotape of Chinook "seizures" fall into this gray zone where we are not sure how to classify them, while a few of the verbal reports we received describe more classic seizures.
Does it matter what we call these episodes?
Before the human genome project began identifying the genes responsible for disease, we had to use clinical criteria for making a diagnosis such as hereditary epilepsy. Now that we can see what gene is responsible, we are finding that some diseases which look very different clinically can be caused by mutations in the same gene. For example, we now know that mutations in one gene (a gene for a calcium channel) can cause a type of epilepsy in mice while mutations in the same gene in people can cause either episodic ataxia (attacks of incoordination) or a type of migraine headache. Human families have been found where the patients have epilepsy as children then develop paroxysmal dyskinesias as adults. So it is possible that genetically as well as clinically there is overlap between these conditions. One theory holds that these paroxysmal dyskinesias are essentially seizures of the basal nuclei, and there is some good evidence to support that idea.
Even though the same gene or genes may be culprits in these different diseases it is still important to be able to distinguish the different clinical syndromes so that we can be certain just what it is these different mutations are doing. It may make a big difference in terms of what drugs work best and what the long range outlook for the dog is. For example, while classic epilepsy in dogs can create life-threatening seizures, paroxysmal dyskinesias may not carry the same risks. People with paroxysmal dyskinesias often experience a decrease in episodes as they age while epileptic dogs tend to get worse with time. Some medications are effective against both diseases while others might only help one or the other. As we search for the genes responsible for diseases in dogs, we have to be able to clearly differentiate these variations on the theme if we hope to make progress. With your help, however, that progress can be made.
Are these always genetic diseases?
Seizures and movement disorders can be either acquired or hereditary. Damage to the brain, such as might occur following severe head trauma or an infection of the brain, can cause these symptoms in some dogs. In other cases, there is no obvious inciting factor, and we see a strong family tendency. DNA studies have found genes that are responsible for some forms of epilepsy and episodic movement disorders in people. So we know that these diseases can have a hereditary component. When we see a condition like this show up in one particular breed of dog, we have to worry that it too may be hereditary. Classic seizures have been described in numerous breeds of dogs, but we've never seen anything quite like the Chinook "seizures" in other breeds.
Most hereditary diseases are recessive traits, which means that dogs can be carriers of the defective gene, but never show signs of the disease. This makes it difficult to eliminate if the gene is widely distributed in the population. While the canine genome map is still far behind its human counterpart, the same techniques can be applied to solving genetic problems in dogs. It requires courage on the part of the breeders to face a problem head on, but the reward could be elimination of the problem from the breed. It will also take a commitment for the long haul, since it will require sampling large families to allow the type of testing that is necessary to do DNA mapping. See the GNN site for a discussion of gene mapping techniques.
How you can help.
As part of the Canine Epilepsy Project, we have collected DNA from over 100 Chinooks in families with the "seizure" disorder. We would like your help in identifying other dogs with the condition and better understanding whether these are indeed true seizures or not. Not only will this help with DNA studies but may lead to improved treatments for affected dogs.THE IDENTITY OF DOGS PARTICIPATING IN THE PROJECT IS KEPT CONFIDENTIAL.
If you have a dog that has episodes that you suspect might be one of these "seizures", here's how you can help.
1) Have your dog examined by a veterinarian. Some seizures can be life-threatening and your first concern should be to ensure that dog is not in danger (see "When is it an emergency?" for details). Other things such as electrolyte problems or low blood sugar can cause episodes of weakness, and there are many things which can cause classic epilepsy. Routine laboratory tests (complete blood count, serum chemistries including creatine kinase (CK), liver function test such as bile acids, thyroid function tests) would be in order to rule out some of these causes.
Some other tests which may be warranted include pre and post exercise lactates/pyruvates, brain scans, or spinal fluid analysis. You may want to ask your veterinarian to refer you to a Board Certified Neurologist if they need help with some of these tests. As discussed above, an EEG would also be valuable, but would certainly require referral to a neurologist who has EEG capabilities. Ideally the samples for glucose and electrolytes would be collected and the EEG would be run during an episode, but this can be easier said than done unless your dog has prolonged spells. Although the research project cannot cover your costs for these tests, they may be important for you dog's sake as well as helping ensure the success of the research, so talk to your veterinarian about them. If you download the forms from this web site before your visit, your veterinarian could collect the blood sample for DNA studies at the same time as the routine blood tests. Alternatively, it could be taken when annual heartworm checks are performed.
2) Grab a video camera and tape the episode. If your dog does not require immediate veterinary care, try to catch an episode on tape to help with our research. Include the whole dog in most of the tape, but also take a brief close-up of the face so that we can see if there is any twitching or jerking of the face. Note how long the episode lasts since undoubtably the very beginning will be missed. Try to determine if the dog is conscious and responsive during the episode. Call his/her name or walk past and see if they follow you with their eyes. Try standing them up and see if they can walk with assistance. Feel the limbs and see if they feel stiff or sensitive to touch. Observe any salivation, urination, or defecation. Note the color of the gums, tongue or inside of the lip (be careful not to be bitten since dogs with true seizures may chomp their jaws violently). If you can, take the dog's heart rate by feeling a pulse inside the hind leg and take the temperature with a rectal thermometer (ask your veterinarian to show you how to do these). You can use the sound portion of the tape to give us a narrative of what the dog was doing before the episode began (were they sleeping, resting quietly, playing vigorously, eating, etc.) or other relevant information.
3)Participate in the genetic study. The more dogs we have DNA from, the better our chances of determining if this is a genetic disease and ultimately finding the gene responsible. When doing DNA studies, we are comparing the genes in affected dogs with those in dogs without the "seizures". Thus samples from unaffected litter mates, parents and some unrelated dogs are as important as those from the affected dogs. This also means that sometimes we contact people for samples because we suspect their line is clean of the disease so that we can get those control samples. If you submit DNA from a dog who has is classified as unaffected, and they subsequently have an episode that could be these "seizures", be sure to contact us so that we can properly classify the dog.
See "Sample Submission" section for information for your veterinarian on collecting and submitting DNA samples. You can also download the sample submission forms. These forms must accompany the samples along with a copy of the pedigree so we can properly place the dog in the family tree.
4) Complete the Seizure Survey. If your dog has had what you think may be one of these "seizures", please also complete the Seizure Survey.
5) Update information. If you've already sent us information, THANKS! Things can change, however. A previously unaffected dog may have an episode, medications may work or stop working, an abnormal blood test may turn up, etc. After seeing this tape, you may decide your dog has these types of episodes when you thought they were unaffected. If such information arises, please let us know so we can keep our data accurate.
6) Support the research. Funding for this research comes exclusively from breed clubs and the AKC Canine Health Foundation. Thank you for your ongoing support.
Contact us if you have any questionsLast updated: 5/17/02