Epilepsy Clinic

Epilepsy

Epilepsy is the most common chronic neurological disorder in dogs and cats. The term "epilepsy" simply refers to the state of recurrent seizures. Seizures are caused by an electrical short-circuit of one or more brain areas which might be followed by contractions of skeletal muscles. In the normal brain, neurons communicate using electrical and chemical signals. Those signals can either be excitatory (activating) or inhibitory. A balance between those two types of signals determines whether neurons will be activated or inhibited. If it is not balanced and neurons are getting more activated more and more neurons fire at the same time, an electrical short-circuit develops and your animal might show seizures.

Epilepsies can have a genetic cause (idiopathic epilepsy), can be symptomatic (secondary epilepsy) - meaning we can identify the underlying cause for the seizures or be cryptogenic. Cryptogenic epileptic seizures are believed to be due to an underlying unidentified brain disease.

Seizures can be classified as:

Focal

Simple

Complex

With or without 2nd generalisation

Primary generalised

Tonic-clonic

Tonic

Clonic

Myoclonic

Atonic   

Absences

Focal seizure

Focal seizures affect one part of the cerebrum of the brain and may cause abnormal movements of specific body parts. These can be stereotyped contraction of a muscle or group of muscles (such as twitching of an eye) or be movements that resemble voluntary motor movements (automatism) such as chewing or running.

Focal seizures not always involve twitching of muscles. Some focal seizures might be just an abnormal sensation, although this can be difficult to determine in dogs. What kind of seizure your pet has depends on what part of the brain is involved.

Focal seizures can start in one part of the brain and can then secondary generalise. When secondary generalisation happens the whole brain will fire simultaneously and you will see your dog's body twitching.

Cross section of the brain showing the movement of a focal seizure Cross section of the brain showing the movement of a focal seizure

Primary generalised seizure

Primary generalised seizures activate the whole brain right from the start. Generalised seizures might be tonic, myoclonic, clonic, atonic, tonic-clonic or absences.

Cross section of the brain showing a primary generalized seizure

Phase of seizure

Appearance

Tonic

Sustained, increased muscle contraction ?

animal usually becomes recumbent in this phase

Myoclonic

(noun = myoclonus)

Sudden, brief, involuntary, single or multiple contractions of muscles or muscle groups.

Clonic

(noun = clonus)

Regularly repetitive myoclonus, which involves the same muscle groups, and is prolonged.

Atonic

Sudden loss of muscle tone, usually lasting 1-2 s or more.

Tonic-clonic

Sequence consisting of a tonic phase, followed by a clonic phase

Eventually absences

(previously known as ?petit mal?)

Brief impairment of consciousness without loss of muscle tone

Rare or non-existent in dogs, or just difficult to detect clinically.

Common form of generalised seizure in humans especially in children.

Seizures can have four stages:

Prodrome

Behaviour changes that occur hours or days before the seizure

Aura

Event prior to seizure characterised by sensory, psychosensory and experiential symptoms in humans, and indicative of a sensation. Humans describe sensations such as fear, déjà vu, a smell sensation or a typical taste

Ictus

The seizure event itself

Post-ictal phase

Behaviour changes hours or days after the seizure

Most seizures are self-limiting. However, some of our pets will have more then one seizure a day (cluster seizures). Some seizures are not self-limiting and are continuous over 30 minutes (status epilepticus). If your dog has a seizure longer than 5 minutes or more than two seizures a day, you need to visit your vet immediately. It is known that seizures are very distressing for the pet owner and may appear longer for us than they actually are. Thus, it is important to time the seizure.

Why is it so important to go straight to the vet? We know from epilepsy research that a seizure longer than 30 minutes can damage the brain significantly.

Epilepsy Clinic     These pages maintained by the Epilepsy Clinic     Contact: epilepsy@rvc.ac.uk


This page was last modified on 02 April 2014