Marg Pough

Seizures are one of the most frustrating things to deal with. I attended a seminar on seizures at a Molecular Genetics conference; even the veterinarians and scientists working in the field know there are many causes.

Seizures are a result of anything that can cause an uncontrolled electrical outburst in the brain. They can vary -very mild, staring episodes, -slight stiffening and shaking but the dog is aware -grand mal types where the dog loses consciousness (tonic/clonic seizures) -or those that are twitching episodes or tics. Duration can be from seconds to hours. Some dogs give signs when a seizure is approaching (prodromal). Other seizures come on suddenly. Many dogs do not have the "typical, grand mal" type of seizures. Veterinarians may not recognize that the milder forms can be a type of epileptic seizure or an episode from some other cause.

Seizures can be caused by brain malformations, trauma to the brain, or trauma to the body resulting in a biochemical imbalance. Toxins, viruses, and bacterial infections can all cause seizures. Liver malformations [portosystemic vascular anomalies (PVSA) "liver shunts" or hepatic microvascular dysplasia (HMVD)] and liver disease can cause "seizures" because of the buildup of metabolic toxins. All such causes must be ruled out before a diagnosis of "idiopathic epilepsy" is backed into. All seizures should be considered to have a genetic basis until proved otherwise.

Seizures in puppies and dogs under a year of age are often caused by brain malformations, liver anomalies (PSVA),or viral/bacterial infections. Complete physical work ups including CAT scans are needed to rule out such physical or infectious etiologies. Urinalysis, paired bile acid and serum chemistry panels should be performed to rule out liver malformations or disease.

Seizures that start in very old dogs are often caused by brain tumors or pancreatic tumors. These may start gradually. For example, the first sign may be behavioral "differences," and then an increase in frequency and severity of the episodes that may lead to classic seizures.

Owners of a dog that has seizures need to keep very careful records. They need to record date, time, and duration of the seizure. If they can videotape an episode, it may help the veterinarian. Some neurologists suggest that the owners describe in writing what they see as each seizure is occurring. Each episode needs to be noted. Does the dog act differently before the episode? Has the dog been ill before the seizure started? Are the seizures associated with feeding, with exposures to chemicals, or to some difference in the environment?

Dogs with recurring episodes of shaking, muscle twitches, cramping, or other "atypical" seizure-like activity may have liver malformations - porto-systemic vascular anomalies (PVSA); these include porto-hepatic shunts [blood by-passes the liver] or hepatic microvascular dysplasia (HMVD)[abnormal or no blood flow within the liver]. An episode may present as if the dog has intestinal cramps or is uncoordinated for a brief period. This may progress to what appears to be leg cramps or incoordination, or such dogs may present with typical seizures. Episodes may vary in duration. Episodes may be associated with eating high protein diets. Most episodes from PSVA do not occur in the regular pattern that is often associated with epilepsy. Some of these dogs may drink and urinate excessively as they try to flush "toxins" from their body. Liver biopsies taken from all lobes of the liver, can be done to confirm HMVD in symptomatic dogs, where obvious shunts are not apparent. Invasive surgery for biopsies is NOT recommended in asymptomatic dogs that have abnormally elevated liver function tests (paired bile acids). Affected dogs do not respond to normal seizure drugs, but may do well on specialized vegetable source protein diets (Hills K/D or L/D, the Iams Liver diet, or a home-cooked Tofu and rice diet.).

A single seizure or cramping episode in a dog of any age does not mean the dog is epileptic or has PVSA. Trauma, exposure to toxins that cause liver or kidney damage, hypocalcemia (in a whelping or nursing bitch), hypoglycemia in a severely stressed working animal, fever, or immature liver function have all been implicated in seizure activity. A dog that has one seizure should not be instantly placed on phenobarbital or other anticonvulsants. Most veterinarians wait to see if there is another episode, and meanwhile try to rule out other causes. Many epileptic (regularly recurring) seizures can be controlled with phenobarbital. Where there are recurring episodes some neurologists put the dog on an anticonvulsant to help block the "learning of seizure pathways in the brain." Epileptic seizures that do not respond to phenobarbital can sometimes be controlled with potassium bromide or a combination of potassium bromide and phenobarbital. However, long term use of anticonvulsant therapy is not without risk. Dogs on any medication must be monitored to be sure the medication is at therapeutic levels (different dogs have different metabolisms), as well as to monitor liver and kidney function.

If you have a dog that has recurring seizures or shaking or twitching/cramping episodes, your responsibility is to tell the breeder. You should also have a complete workup to attempt the best diagnosis. The breeder's responsibility is to keep track of reported cases. A breeder may wish to remove a dog from a breeding program, or at least to change breeding strategies, if they know a dog is producing affected dogs. If owners do not tell the breeder, the breeder can not make informed decisions. Certainly there are inherited forms of seizures in Borders. But not every dog that has a seizure has an inherited form. DO NOT GO AROUND BLAMING DOGS OR BREEDERS. Most dogs, that produce a dog with seizures, do not have seizures themselves. Geneticists do feel that affected dogs should not be bred. There is no one "seizure gene" for all breeds, there are different mutations in different breeds, and there may be multiple mutations within a breed. Owners and breeders need to keep careful records, and pedigrees. Ideally, breeders should construct genograms (vertical pedigrees which indicate all puppies in each litter) rather than horizontal pedigrees. Geneticists need to know the number of unaffected dogs as well as affected dogs in a kindred. Idiopathic epilepsy and PSVA are different disorders, correct diagnosis is extremely important if we are to successful work to reduce their incidence.

A number of different breeds are known to have PSVA; the anomalies range from simple shunts, which are often able to be ligated if there is adequate blood flow through the liver, to HMVD or shunts with HMVD. PSVA does not appear to have a pattern of simple inheritance in the breeds where it has been studied in depth (Cairn Terriers and Yorkshire Terriers.) Affected dogs should not be bred. In an asymptomatic dog with abnormal bile acids, careful consideration needs to be given as to whether or not to use that dog in a breeding program.

Dr. Sharon Center at Cornell states in an article on Portosystemic Anomalies: "The entire picture of a dog’s health must be used to make [breeding] judgements. The severity of differences in abnormal bile acid values CANNOT and SHOULD NOT BE USED TO SELECT BREEDING DOGS. If you do this, you will likely reject some beautiful genetic traits. However, if you have an unprecedented prevalence of PSVA in a kindred, STOP reproducing that line.

At the present time, we believe that you cannot breed the MVD gene out of a dog breed. We have observed totally normal parents produce affected offspring. The MVD trait likely is polygenic, similar to the complexity of hip dysplasia. A lot of good dogs can be wasted by culling based on bile acid values.

A German Veterinarian and breeder recognized a health problem in her line. Many of the breed were tightly linebred, which may be why the problem surfaced. Dr. Center has examined tissues that she sent, and has confirmed HMVD. Owners in Europe and in this country, have sent pedigrees to her. Her data include over 140 dogs suspected to have this condition. We are cooperating with her, and she is working with a geneticist. Construction of genograms from pedigrees takes time. Correct diagnosis is important to distinguish idiopathic epilepsy from PSVA/HMVD. In the US many different laboratories have been used for liver function tests (paired bile acids). When reporting such results it is extremely important to include the laboratory’s normal ranges. Liver biopsies, done to determine treatment strategies, should be examined by the pathologist the surgeon normally uses.

Marg Pough is a long time breeder and exhibitor of Border Terriers and has served as Chair of the BTCA Health and Genetics Committee since 1971. An AKC licensed judge, Marg’s education has been in the field of Vertebrate Biology. Presently, she is employed at the Diagnostic Laboratory of the New York State College of Veterinary Medicine at Cornell University, Ithaca, N.Y. The above article was written for the Summer 2000 issue of the Borderline, the quarterly magazine of the Border Terrier Club of America.