A seizure, also called a convulsion, is the clinical manifestation of excessive and abnormal electrical activity in the cerebral cortex of the brain. Epilepsy refers to recurrent seizure activity, which may be acquired (such as from a brain tumor or scar tissue) or idiopathic (which means of unknown origin).
Causes of Canine Seizures
Seizures in domestic dogs can be caused by either intracranial (inside the skull) or extracranial abnormalities. Intracranial causes of seizures include genetic disorders, infection (viral, fungal or bacterial encephalitis), brain tumors, abscesses, metastatic tumors from remote regions of the body, stroke, cysts, primary epilepsy, hydrocephalus and anatomical malformations. Extracranial causes include exposure to or ingestion of toxins (antifreeze/ethylene glycol, lead, metaldehyde, strychnine or other rodent bait, insecticides/organophosphates, chocolate), heat stroke, liver disease, kidney failure, direct head trauma, canine distemper virus, sudden drop in blood sugar (hypoglycemia; common with overdose of insulin in diabetic dogs), portosystemic shunt, low blood calcium (hypocalcemia; such as from eclampsia ["milk fever"] or hypoparathyroidism) and other metabolic abnormalities.
Since there are so many, potentially unrelated causes of canine seizures, there is no particular way to prevent them from happening. However, once diagnosed, primary epileptic seizure disorders usually can be fairly well-managed with medication. Dogs known to have seizures or that are otherwise suspected to have epilepsy should not be bred.
Most dogs with primary seizure disorders will require lifelong treatment. Although they are fairly common, seizures in companion dogs should be taken very seriously. Sometimes, other medical conditions cause clinical signs that mimic seizures. These should be attended to, as well. Owners who think that their dog may be having seizures should consult with their veterinarian.
Seizures are caused by abnormal electrical impulses in the cortex of the brain. These impulses cause a combination of uncontrollable, involuntary and excessive or reduced muscle activities. There are a number of different causes of seizures in domestic dogs. However, the symptoms are fairly classic and easily recognizable.
Symptoms of Seizures in Dogs
Seizures tend to be transient and to start and stop abruptly. Most generalized seizures (also called "grand mal" seizures) start with a period of altered behavior, called the "aura." During this period, owners may notice one or more of the following signs:
Far-away look in the eyes
Unusual clinginess; attention-seeking behavior, or seeking of seclusion
The actual seizure event normally lasts for about two minutes or less and is characterized by one or more of the following symptoms:
Loss of awareness of the immediate environment
Rigid extension of the extremities
Loss of consciousness
Cessation of breathing (for roughly 10 to 30 seconds)
Rhythmic jerking or paddling of the legs while lying down (resembles running)
Muscle twitching (especially facial muscles)
Teeth chomping; chewing
Excessive salivation (ptyalism; drooling)
Generalized seizure episodes can last from seconds to minutes. In the time immediately following a seizure (called the post-ictal period), the dog begins to recover. She may still experience temporary blindness, confusion, sleepiness, disorientation and post-seizure convulsions during this period, which typically lasts for about an hour but can last for several days. Dogs with primary epilepsy usually have recurrent seizures that become increasingly frequent over time. Dogs can also have focal or localized seizures, which only affect a limited part of their bodies. These are usually caused by a brain tumor, brain abscess or other focal brain lesion.
Dogs at Increased Risk
Seizures can occur in dogs of any age, sex or breed. Primary seizures, called epilepsy, are most common in dogs between the ages of 6 months and 5 years. Older dogs tend to suffer seizures caused by brain tumors, while younger dogs are predisposed to seizures from ingestion of toxins, metabolic disorders or conformational abnormalities. Breeds that have been reported to have a genetic predisposition to epilepsy include the Beagle, Belgian Tervuren, Dachshund, Keeshond and German Shepherd. Other breeds with an unusually high incidence of epileptic disorders, but without an established hereditary cause, include the Collie, Cocker Spaniel, Labrador Retriever, Golden Retriever, Irish Setter, Miniature Schnauzer, Siberian Husky, St. Bernard, Poodle and Wire Fox Terrier. Mixed-breed dogs can suffer from seizure disorders, as well.
Seizure disorders are not particularly difficult to detect. The difficult part is determining the cause of the seizures.
How Seizures are Diagnosed
Presented with a dog suspected of having a seizure disorder, most veterinarians will recommend a complete blood count, serum biochemistry panel and urinalysis, after obtaining a complete history of the dog's symptoms and conducting thorough physical and neurological examinations. The results of the blood and urine tests may reveal metabolic disorders, intoxication, liver or kidney disease or other abnormalities. In dogs with primary epilepsy, the results of these tests usually are normal. The veterinarian may also recommend an electrocardiogram (ECG) to assess the health of the dog's heart, and thoracic (chest) and abdominal radiographs (X-rays) to look for any visible abnormalities. Dogs with heart disease that involves abnormal heart rhythms (arrythmias) can have clinical signs that mimic primary seizures. If the patient is a puppy under 6 months of age, a serum bile acid assay may be performed to rule out a portosystemic shunt as a cause of hepatic (liver) encephalopathy.
Advanced diagnostics will include more detailed assessment of the brain using computed tomography (CT or CAT scan) or magnetic resonance imaging (MRI). These sophisticated diagnostic tools can identify tumors or other lesions in the brain or skull. Typically, they are only available at veterinary teaching hospitals and specialty clinics. Radiographs of the skull are normally unremarkable and not particularly helpful, unless the cause of the disorder is direct trauma to the head. A spinal tap to obtain a sample of cerebrospinal fluid (CSF) can help to identify certain types of neurological disease and inflammation. If exposure to a particular toxin is suspected, diagnostic blood tests may be productive, as well.
Dogs under 6 months or over 5 years of age that present with signs of seizures probably do not have primary epilepsy. Structural brain abnormalities are a more likely cause of their symptoms. Research is underway to identify a genetic marker for epilepsy. Hopefully, one day breeders will be able to identify dogs as carriers of the "epilepsy gene(s)," so that they can eliminate them from responsible breeding programs.
When a dog has a seizure, its owner is typically and understandably scared and confused. Watching a loved one have a seizure is heartbreaking, but fortunately a number of treatment options are available, depending upon the seizure's cause. Treatment protocols for dogs with seizure disorders are evolving, and there are many new medications in development to help manage these difficult medical conditions in companion animals. The goals of treating seizure disorders are to reduce seizure frequency and severity and to increase the time between seizure episodes (called the "seizure-free interval").
The precise treatment will depend upon the underlying cause of the dog's seizures. Dogs can suffer from seizures for a number of reasons, including allergic reactions, fever, exposure to toxins, trauma, infection, developmental abnormalities and primary neurological disorders such as epilepsy, among other things. In order to treat seizures effectively, the attending veterinarian must figure out why they are happening.
Treating seizures can be as simple as changing the dog's diet, taking steps to reduce a high fever, treating a poisoning event or helping the dog heal after a traumatic injury. However, most seizure disorders require treatment with medication, especially if the dog experiences more than one or two seizures a month, has "grand mal" or generalized seizures, has been diagnosed with epilepsy or has "cluster seizures" that occur multiple times in a 24-hour period. A seizure disorder called "status epilepticus" is a true medical emergency that requires hospitalization; this condition involves continuous seizure activity for more than five minutes, or a prolonged series of seizures without a return to consciousness.
Status epilepticus and cluster seizures require immediate intravenous administration of anticonvulsants to prevent permanent brain damage or death. If blood glucose and/or calcium levels are low, intravenous dextrose and/or calcium may need to be administered on an inpatient basis.
Once the patient is stabilized, chemotherapeutic treatment usually involves administration of phenobarbital and/or diazepam (Valium), both of which are anti-seizure drugs. Propofol can also be administered to hospitalized dogs with persistent seizures. The appropriate dosage, route and length of treatment depend upon the severity and cause of the dog's seizures. A newer anti-seizure medication in humans, Neurontin, has been used to treat seizures in dogs with very good results and reduced liver side effects. These medications all require a prescription and must be administered and supervised by a veterinarian. New treatments are constantly under development. Of course, any drug, including anti-seizure medications, can have adverse side effects. Moreover, anticonvulsants are not 100% effective.
Dogs with primary epilepsy probably will require lifelong treatment to control their seizures. Currently, treatment for chronic canine epilepsy involves use of medications such as phenobarbital and/or potassium bromide, in addition to many other drugs. Regular blood tests are important for dogs on long-term anticonvulsant therapy, to monitor blood drug and liver enzyme levels. Alternative therapies, such as acupuncture and dietary changes, have been suggested as being potentially helpful for dogs with seizure disorders.
What to Do During a Seizure
If an owner thinks that his dog is having a seizure, there are some general guidelines to follow. It is very helpful to the attending veterinarian for the owner to keep a log of the time and length of the episodes. Owners should not attempt to grab their dog's tongue, as they may be unintentionally bitten. Dogs normally do not swallow their tongues during a seizure, although infrequently they can catch their tongue between their teeth and cause minor injuries.
If a dog has fallen on a hard surface, such as a cement, ceramic or hardwood floor, it is helpful to place a pillow between the dog's head and the floor to minimize physical injury from the seizure. Animals generate a great deal of body heat while seizing, so they should not be wrapped in layers of warm blankets, even if they appear to be shivering. The shivering associated with most seizures is not caused by low body temperature. If the dog is coming into contact with a chair or another object during a seizure, it is best to move the object rather than the dog, if at all possible. Otherwise, there normally is no need for human intervention. Once the seizure is over, the owner should contact a veterinarian promptly.
The prognosis for dogs with seizure disorders ranges from good to grave, depending upon the underlying cause of the condition. Primary epileptic seizures usually carry a good prognosis and typically can be well-managed with long-term use of oral anticonvulsant medications. Unfortunately, dogs with inoperable brain tumors are at the other end of the prognostic spectrum.