Seizures

[Appylvr]

What would cause a dog to seemingly have a seizure for no reason? I was taking care of my neighbor's animals this weekend and Friday morning after I fed the horse one of their dogs had a seizure.

She was up in some bushes on a hill barking at the other neighbor's dog and when I started walking up towards the house I called her. I looked down to tell her to sit when I was on the patio and she was shaking. Her back legs wouldn't hold her up and she was trying to walk, so she kept falling. I made her lie down and then petted her until it was over. It seemed to last between 3-4 minutes, but it wasn't a bad one (my old cocker spaniel had epilepsy, so I've had a lot of experience with seizures).

I told them about it last night when they got home (they didn't have any cell reception up where they were and I didn't want to worry them while they were gone) and they said she's never done anything like that before...

We thought maybe if she jumped off the hill and hurt herself or something that could have been the reason? Any ideas? Since she's had a seizure now does that mean she's got epilepsy? Or can it be a one time thing?

[sheplovr]

By Teri Dickinson, DVM

With special thanks for editorial assistance from Patricia J. Luttgen, DVM, MS, diplomate ACVIM (neurology), Lakewood CO and Grace Robinson, DVM, Dallas, TX

DEFINITION OF TERMS

A seizure has been defined as "a transitory disturbance of brain function"(1) which results in alterations to behavior and activity caused by abnormal brain function. The terms convulsion, fit and ictus(2) are synonymous with the term seizure. A generalized seizure has been defined as "a period of generalized muscle activity accompanied by loss of consciousness."(3)

Epilepsy3 refers to recurrent seizures arising from a nonprogressive intracranial (located within the skull) disorder. Note that the term nonprogressive means that the cause is nonprogressive, not the severity or frequency of the seizures themselves.

Epilepsy is of acquired or idiopathic origin. Acquired or secondary epilepsy is that in which a previously active brain disorder has left the brain in a seizure prone state. An example might be a dog that is hit by a car and suffers head trauma, but survives. Idiopathic epilepsy is also known as inherited, congenital or primary epilepsy and involves recurrent seizures for which no cause can be identified.(4)

WHAT HAPPENS DURING A SEIZURE?

What happens during a seizure is complex, and not totally understood.(5) In the field of human medicine much research has been devoted to how a seizure actually occurs but many questions remain to be answered.

For our purposes, a simple explanation will suffice. Neurons (nerve cells) in the brain transmit and process information through the creation and conduction of small electrical currents. Normal function of a neuron is associated with a different electrical charge inside the cell than outside. This difference is known as the membrane potential (MP). It reflects the different charges found inside the cell membrane versus outside. Under certain circumstances, this difference is turned into an actual electrical charge, which is passed on to neighboring cells. The neuron is said to have "fired."

Neurons also create special substances, neurotransmitters, which when released, act on the membranes of nearby cells. Neurotransmitters may act to excite or inhibit nearby cells. Normal transmission of information requires a finely tuned combination of excitement and inhibition. A seizure reflects the results of too much excitation, too little inhibition or neurons that are too sensitive to the neurotransmitters.

During a seizure, certain cells (a seizure focus) begin to fire repeatedly and spread this behavior to other cells. A normal brain responds with enough inhibitory neurotransmitters to stop the spread. If a group of neurons "runs away," firing repeatedly and the brain cannot inhibit them, a seizure results. Seizures are often self-limiting as the renegade neurons exhaust themselves and stop firing. The period after the seizure may reflect lower than normal activity among the neurons. How and why the "renegade" neurons cause a seizure is still a matter of much investigation.
PARTS OF A SEIZURE

A seizure consists of three parts, the aura, the ictus and the postictus. The aura signals the beginning of the seizure. It is characterized by behavioral changes such as whining, restlessness, hiding or apprehension. During this stage, abnormal electrical discharges are taking place among the neurons.

The ictus is the seizure stage and is characterized by all the signs associated with the seizure: unconsciousness, muscle activity, salivation, etc. Neurons are firing rapidly and are unresponsive to inhibitory substances.

The postictal phase occurs immediately after the seizure and may last a few minutes to several days. It may be characterized by confusion, wandering, blindness or unresponsiveness. The neurons are exhausted and unable to respond.

TYPES OF SEIZURES

Seizures can be divided into types, based on the signs seen during the seizure and changes to the EEG (a reading of the electrical currents in the brain). Most work on classifying seizures has been done in humans and may not always apply accurately to dogs, but at least two types of seizures are documented in dogs: partial (also known as focal) and generalized.(6)

Partial seizures have signs and EEG evidence that the seizure originates from one area (focus) of the brain. A partial seizure may progress and become a generalized seizure, or may be limited to a specific abnormality such as repetitive motions of a single limb or facial twitches. Partial seizures are commonly associated with acquired causes and brain tumors.

Generalized seizures are also called grand mal, major motor (affecting movement) or tonic-clonic(7) and are characterized by signs and EEG abnormalities that are widespread from the very beginning of the attack. Generalized seizures are usually bilateral (affect both sides), symmetrical, include loss of consciousness, generalized motor dysfunction and sometimes urination and defecation. Idiopathic epilepsy is usually evidenced as generalized seizures.
DETERMINING THE CAUSE OF SEIZURES

In attempting to find the cause of seizures, it is important to remember that seizures are not a disease, but merely a symptom of a disease process. A process of elimination or "rule outs" is used to determine the cause.

The normal brain is capable of seizing in response to a variety of stimuli; therefore, the causes of seizures are many. Causes of seizures can be divided into two major categories, extracranial and intracranial.3 Extracranial causes are those that arise outside the nervous system, (i.e., exposure to toxins). Intracranial causes arise within the nervous system (i.e., brain tumors).

Each of these categories can be subdivided. Extracranial causes can be divided into external or those that originate outside the body (i.e., toxins) and internal or those that originate inside the body (i.e., liver disease). Intracranial diseases can be divided into those that are progressive or nonprogressive. Progressive disorders involve more and more brain tissue over time (i.e., tumors). Nonprogressive diseases do not involve additional brain tissue, although the severity of the seizures may increase over time. Epilepsy, both acquired and idiopathic, is an example of a nonprogressive, intracranial cause of seizures.

Determining the cause of seizures is a process of ruling out possible causes and begins with the veterinarian obtaining an accurate history, conducting a physical exam that includes a thorough neurologic (nervous system) examination, and running basic laboratory tests. A complete blood count, urinalysis and serum chemistries to check for kidney and liver function, hypoglycemia, hypothyroidism, etc. are routinely performed. Any abnormal test results will be followed by more specific tests. Acquired (secondary) epilepsy is usually diagnosed by taking a thorough history, especially regarding trauma (hit by car), anoxia (lack of oxygen due to near drowning, some type of entanglement, etc.) or other such incidents. If the history and subsequent testing fail to reveal abnormalities, an extracranial cause can usually be ruled out.

If an intracranial cause is suspected, more specific tests will be conducted. These may include skull x-rays, spinal fluid analysis, EEG's or possibly CT(8) or MRI(9) scans of the head. Economics and availability of some tests (EEG, CT or MRI) may limit diagnostic options.

If the specific testing for intracranial causes fails to identify abnormalities, the remaining choice is nonprogressive intracranial disease. For the most part, nonprogressive intracranial disease is classified as idiopathic or inherited epilepsy.

Dogs affected with idiopathic epilepsy are usually healthy and completely normal between seizures with no abnormal test results (even EEG)(10) between seizures. Onset of seizures usually occurs between six months and five years of age, although seizures may not be recognized until the animal is older. In some individuals seizures may be triggered by some stimulus: fatigue, stress, fear, etc. In others, onset of seizures seems completely random. Epileptic(11) is the term used to describe individuals afflicted with epilepsy.

It has not been determined if idiopathic epilepsy is an inherited disease in all breeds of dogs. Despite the relatively high incidence of canine epilepsy, very little active research is being conducted in dogs.(12)

A review of the literature indicates that inheritance has been proven or is strongly suspected in the following breeds; Beagles,(13) German Shepherds (Alsatians-England)(14), Belgian Tervurens,(15) Keeshonden,(16) Dachshunds(17) and Horak's laboratory dogs (Czechoslovakia).(18) Many breeds are also reported to have a higher than average incidence of affected individuals, which may also point to a genetic component. Among these are Poodles, Cocker Spaniels, and Irish Setters.(19) The incidence of affected individuals in various dog populations is reported to be between 0.5% and 5.7%10,(20). No reports appear in which idiopathic epilepsy is proven not to be an inherited disease.

Three selective breeding studies of dogs produced incidences of 38%,(21) 66%(22) and 100%15 epileptic offspring when both sire and dam were epileptic. Another study documents an incidence of 63%(23) epileptic offspring produced from an accidental breeding of two related, epileptic individuals. Two of these studies15,19 also noted a very early onset (6-8 weeks of age) of seizures in these litters.

Pedigree analysis in several above mentioned breeds demonstrates a familial (occurring in more members of a family than expected by chance) pattern of inheritance. Studies of humans, mice, rats and rabbits leave little doubt that epilepsy in these species is inherited. Mice are common animal models for epilepsy in humans, and work is under way identifying the specific genes that cause the epilepsy.(24)
Cunningham and Farnbach,18 in a study supported in part by the Irish Setter Club of America, reached the following conclusions:

"Until the genetic mechanisms involved are more clearly understood, it seems prudent for veterinarians to advise owners of epileptic dogs that:

1) The idiopathic form of canine epilepsy may have a major genetic component.

2) It generally is impossible, without considerable test breedings, to determine the degree of involvement of either the sire or the dam in producing epileptic offspring.

3) It is unwise to breed an epileptic dog or to repeat the breeding that produced it, and it is probably unwise to breed its litter mates."

TREATMENT OF SEIZURES

Treatment of seizures varies widely according to the cause. External extracranial causes such as environmental toxins (lead, insecticides, etc.) require removal of the offending substance from the animal's environment. In addition, specific treatments may be required to counteract the effects of the toxins and anticonvulsants (drugs used to control or prevent seizures) may be required to control the seizures.

Internal extracranial diseases require identifying the disease process and providing the specific treatment. These disease processes include fungal infections, kidney or liver disease, hypothyroidism, viral infections (i.e., distemper or rabies), and hypoglycemia.

Intracranial diseases include tumors, congenital defects (i.e., hydrocephalus) and infarctions (loss of blood supply to an area). Therapy includes specific treatment of the primary disease (if possible) and anticonvulsants as needed to control seizures.

Anticonvulsants are usually the only treatments given for idiopathic epilepsy. Not all affected individuals require drug therapy. The decision to treat epileptics is usually based on several factors: frequency and severity of seizures, likelihood of owner compliance with a treatment regime, and known side effects of anticonvulsants. Despite their frightening appearance, infrequent grand mal seizures of 1-3 minutes duration with no abnormalities remaining after the seizure are generally not dangerous to the patient.

In treating seizures, the goal is to keep seizures to a minimum, while avoiding serious side effects. All anticonvulsants have some undesirable side effects and require regular monitoring of the patient. LeCouteur and Child3 recommend anticonvulsant therapy for dogs known to have one or more seizures per month, unless animals have clusters of seizures or episodes of status epilepticus (rapidly repeating seizures with no period of consciousness between them). These animals should be treated regardless of the length of the interval between seizures. Status epilepticus is a medical emergency and requires immediate treatment.

Skerrit2 states that 60-70% of all treated cases have a reasonable measure of control with proper, monitored, anticonvulsant therapy. A variety of drugs are used to treat seizures. At present, phenobarbital is considered the drug of choice. Additional drugs may be added to the treatment protocol if the level of control is not satisfactory.

HOPE THIS HELPS HONEY DO NOT FEAR THERE IS A REASON AND IT WILL BE OK, RELAX AND CONTACT THE OWNER.

[Appylvr]

Wow! That's a long post Sheplovr! I scanned it, but I don't have time to read the whole thing right now... I'm at work and my lunch is almost over...

The owners are back, I told them about it last night when they got in. I just remembered they both said she ran into the wall once and knocked herself out, but that was a couple of years ago. It might be possible that she's had more seizures but they were never there when it happened?

My old cocker spaniel, Chester had epilepsy. I got him from a friend when he was 2 years old. They never mentioned that he had it and one morning we saw him having a seizure and freaked out. We rushed him to the vet thinking he had gotten into something, like poison. The vet told us what it was and what to do. He lived up until he was 17, we did have to keep him on medicine for it though, he used to have really bad ones. The reason Chester had it was because my friends later told me he was in a car wreck when he was a puppy...

[sheplovr]

I am so sorry sweetie try and read some so u can assist and know what causes these, I had a dog many moons ago take them, but forget why, just trying to help you out, not to hurt u honey. Just skim through and learn the reasons, it might help honey sorry so long but did not want to let anything out, love you.

[rottiegirl]

Appy, my Yorkie has occasional seizures. Medication has no effect on him. If they aren't grand mal seizures, or they don't happen very often I have been told that it isn't a big deal.

[SalemsMom]

I had a Scotty that had seisures, and we gave her medicine for it. Sometimes the medicine worked and other times it didn't. She lived untill she was 8 years old, and died having one. A friend had a Jack Russel who died at a year old, when she had one, but I know of others that lived to a ripe old age of 15 years. I would say whether it was a small one or a grandma seisure,and if she does well with the medicine.