Seizure Classification: Videos of Episodic Events in Dogs and Cats
World Small Animal Veterinary Association World Congress Proceedings, 2004
Joane Parent, DMV, MVetSc, ACVIM (Neurology)
Ontario Veterinary College

This conference uses videos of transient events in dogs and cats to demonstrate the variability of episodic events that occur in these species. Seizures, movement disorders, behavioral and sleep disorders will be shown. The origin of some of the events displayed on videos is not always known since electroencephalographic data is lacking in veterinary medicine. In the last few years, there have been significant changes brought to the human ILEA (International League Against Epilepsy) seizure classification. Using this classification, veterinary neurologists are trying to reach a consensus on the definition and terminology of the words used to describe seizure activity and on some of the events observed in dogs and cats.

Seizure classification

We distinguish two types of seizures:

1.  Generalized seizure (convulsive or not)

2.  Focal (partial) seizure:

a.  Simple

b.  Complex (with or without generalization)

The differentiation between focal and generalized seizures is based on consciousness. If the animal is unconscious, the seizure is generalized. The generalized seizure can be convulsive or non convulsive. If consciousness is present, the seizure is focal (partial). In complex focal (partial) seizure, consciousness is present but altered whereas in simple focal (partial) seizure, consciousness is preserved. Since the motor neuron system in domestic species is polysynaptic, it is doubtful if the simple focal (partial) seizures occur.

Although the classification is roughly the same among species, the symptomatology between species differs. Complex focal seizures, with or without secondary generalization, are the most frequent seizures in the cat. These seizures may be violent, the animal propelling itself in the air, biting his tongue, avulsing his claws, yet at other times, only the ears, eyelids or whisker fluttering and twitching are observed. In dogs the most common seizure is the seizure that has a short aura and that rapidly progresses into a convulsive tonic-clonic (generalized) seizure.

Epilepsy classification

The International League Against Epilepsy (ILAE) has modified its terminology in the last few years. The epilepsy is idiopathic when the syndrome is only epilepsy, with no underlying structural brain lesion or other neurological signs or symptoms. This epilepsy is presumed to be genetic and usually age dependant". (ILEA). The epilepsy is symptomatic when "the epileptic seizures are the result of one or more identifiable structural lesions of the brain" (ILEA). The epilepsy is likely symptomatic when "the epilepsy is believed to likely be symptomatic but no etiology has been identified". Symptomatic and likely symptomatic epilepsies are the only epilepsies that we have diagnosed in the cat.

Cluster seizures and status epilepticus

The seizures are occurring as a cluster when there is more than one seizure observed per 24-hour period. It must be recognized, because the patient experiencing cluster seizures should be treated as a potential emergency. The animal is in status epilepticus when the seizure is prolonged lasting 30 minutes or more, or when there is a rapid succession of 3 or more seizures with the consciousness remaining impaired between seizures and the series lasting 30 minutes or more. Status epilepticus, like seizures, can be focal or generalized. The latter is often convulsive in dogs. Convulsive status epilepticus is a medical emergency because of the life-threatening metabolic dysfunction that ensues.

Sleep Disorders

These are not only poorly described, but also poorly recognized in veterinary medicine. When present, they occur regularly, almost every time the animal reaches the necessary level of sleep. The animal remains asleep after the abnormality. Conversely, the animal after a seizure is awake and often disoriented. The seizures are frequently observed while the animal is resting, dozing, in the early stages of sleep.

Behavioural disorders

There is controversy on the origin of the behaviour of the dog that chases its tail or catches flies or other repetitive behaviours. In this author's opinion, these behaviours are too focused and directed to be seizure activity. A seizure is a transient decerebration and as such cannot manifest itself as a complex goal directed behaviour.

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Speaker Information
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Joane Parent, DMV, MVetSc, ACVIM (Neurology)
Ontario Veterinary College

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