Seizure Disorders in Dogs
A seizure is caused by an abnormal burst of electrical activity within the brain, commonly in one of the cerebral hemispheres. The electrical activity sometimes spreads out and involves other areas, including the midbrain.
A typical grand mal seizure is preceded by a period of altered behavior, called the aura. During the aura dogs may be restless and anxious, cry out, demand affection, or seek seclusion. The actual seizure normally lasts less than two minutes, and is characterized by collapse with rigid extension of the legs. The dog becomes unconscious and may stop breathing for 10 to 30 seconds. This is followed by rhythmic jerking of the legs (which resembles running or paddling). Some dogs also chomp, chew, drool, or urinate and defecate. As the dog regains consciousness there is a postseizure state characterized by disorientation and confusion. The dog may stumble into walls and appear blind. The postseizure state can persist for minutes or hours. Grand mal seizures are typical of epilepsy.
A focal motor or partial seizure is one in which the jerking or twitching is limited (at least initially) to a particular part of the body. A focal seizure usually indicates a specific brain lesion, such as a scar, tumor, or abscess.
Seizures are commonly associated with brain injury, encephalitis, heat stroke, brain abscess, brain tumor, stroke, poisoning, kidney failure, or liver failure. Seizures associated with a concussion frequently occur weeks or months after the head injury and are caused by a focus of scar tissue in the brain.
Postencephalitic seizures occur three to four weeks after the onset of encephalitis. Distemper, in particular, is characterized by attacks that begin with chomping, tongue chewing, foaming at the mouth, head shaking, and blinking, all followed by a dazed look.
Postvaccination seizures have been described in puppies under 6 weeks of age following inoculation with a combined distemper-parvovirus vaccine. This is extremely rare with current vaccines.
A bitch may develop low blood calcium levels after whelping and have seizures. A sudden drop in blood sugar (hypoglycemia) can also trigger a seizure. This occurs in newborn pups with cardiopulmonary syndrome. It can also occur in small-breed puppies who have not been fed adequately. A common cause of hypoglycemia is giving too much insulin to a diabetic dog.
Common poisons that cause seizures are animal baits such as strychnine, antifreeze (ethylene glycol), lead, insecticides (organophosphates), and chocolate. Seizures caused by organophosphates are preceded by drooling and muscle twitching. Exposure to a spray, dip, or premise treatment suggests the diagnosis.
There are a number of conditions that, while not true seizures, are often mistaken for them. Bee stings, for example, can cause frenzied barking followed by fainting or collapse. Cardiac arrhythmias can be mistaken for seizures because they cause loss of consciousness and collapse.
Treatment: If the dog is in a dangerous location at the time of the seizure, move her to a safe site. Otherwise, do not disturb the dog during or after the seizure, as this may trigger further seizures. Despite the old wives' tale, do not pull out the dog's tongue or wedge something between her teeth. Dogs can't swallow their tongue.
Note the length of the seizure. As soon as the seizure is over, notify your veterinarian, because he or she will want to examine the dog to diagnose and treat the underlying cause.
Seizures lasting more than five minutes (status epilepticus seizures) or cluster seizures (several seizures one after the other without a return to consciousness) are emergencies. They must be stopped with intravenous Valium or other anticonvulsants to prevent permanent brain damage or death. Seek immediate veterinary attention. Status epilepticus has a poor prognosis, because it is usually caused by poisoning or a serious brain disease.
If seizures cannot be controlled with phenobarbital and potassium bromide, other drugs, such as Clonazepam, Valproic acid, Clorazepate, and many others can be added. The dosages and rates of action of all anticonvulsants are variable. Regular monitoring of serum drug levels is essential-both to control seizures and to avoid toxicity. Liver enzymes are monitored as well. The two common causes of treatment failure are not maintaining adequate drug levels and not giving the drugs as often as directed. A missed dose of an anticonvulsant can precipitate a seizure. It is important to work closely with your veterinarian.
Acupuncture and dietary changes may also help to reduce the number and extent of seizures.
Research is under way to identify the defective gene or genes responsible for epilepsy so that dogs can be identified as carriers before being bred. Affected dogs may not have their first seizure until 3 to 5 years of age, by which time they may have already been bred. No dog known to seizure from suspected epilepsy should be bred.
This article is excerpted from “Dog Owner’s Home Veterinary Handbook” with permission from Wiley Publishing, Inc.
Copyright © 2007 by Howell Book House. All rights reserved.