Epilepsy is not a specific disease but a chronic condition characterised by recurrent seizures. A patient having a single epileptic seizure does not have epilepsy. Remember that an epileptic seizure is not a disease but a clinical sign, generally indicative of a forebrain disorder. The primary question when faced with an animal that has had seizures is whether these are epileptic in nature. Epilepsy shows no sex predilection, and in idiopathic epilepsy the first seizure usually occurs between 6 months and 5 years of age. A breed predisposition is reported with GSDs, Irish Setters, Keeshond, Golden retrievers, Labradors, Belgian shepherds, American Cockers and Alaskan Malamutes being over-represented. Epilepsy can occur secondarily to an underlying structural disorder of the CNS eg congenital malformation, a space occupying lesion, ischaemia or traumatic scar. If there is an underlying disease the condition is termed symptomatic epilepsy. The term idiopathic epilepsy is reserved for cases where investigations have failed to reveal an underlying cause and none is suspected.
Seizures can be classified according to their presentation (vs. physical manifestations), as focal or generalised. In dogs, generalised seizures (with impaired consciousness and bilateral motor activity) are the most common type. Cats relatively commonly exhibit focal seizures, which may be motor or psychomotor events. Any part of the body can be involved during a focal seizure depending on the region of the brain affected.
Image: Lhasa cross exhibiting torticollis as part of a focal motor seizure - courtesy of Simon Platt, AHT.
The time interval between seizures varies between animals and may decrease with time. Some animals have seizure clusters, ie a number of seizures occur within a 24 hour period, but there is then a prolonged interval before the next seizure. Other animals have multiple seizures with a constant time interval between each.
The diagnosis of primary idiopathic epilepsy is a diagnosis of exclusion.
In many cases the vet is never present during a patient’s seizure and relies entirely on the owner’s description of events. Collection of a detailed history is therefore important and a structured, standardised questionnaire may be useful. The description of events can aid in the classification of the seizure and may provide useful diagnostic clues to its aetiology. Accurate record keeping allows monitoring of progression/regression of signs with time. A typical history for epileptic seizures suggests a forebrain abnormality and includes the following points about the actual events:
• Seizures occur at rest
• Tonic/clonic seizure with brief loss of consciousness
• Stereotypical event
• Regular interval between seizures (which may become shorter with time)
• Pre- and post-ictal phases may be identified (typified by transient changes in behaviour, wakefulness and occasionally vision).
Accurate history taking may help to eliminate potential mimics of epilepsy such as narcolepsy, cataplexy and syncope. Download the veterinary history checklist
Seizures may take a number of forms ie generalised or focal (depending on the area of brain affected). The signs shown during the seizure depend upon the location of the abnormal electrical activity within the brain and may be motor (muscle twitching), sensory, or psychic (producing emotional sensations). Most dogs with idiopathic epilepsy have generalised motor seizures.Typical signs include:
• Loss of consciousness
• Initial rigidity followed by tonic/clonic activity
• Autonomic dysfunction such as salivation
Prodromal – seen in 10% of epileptic dogs. This phase lasts for minutes to days before the seizure and, in dogs, most commonly manifests as restlessness.
Aura – This phase lasts for a few seconds to minutes before the seizure and is probably a focal seizure which rapidly generalises. It represents the initial abnormal electrical activity in the brain. Behavioural, motor, sensory or autonomic dysfunction may be evident.
Post-ictal – This can last for hours or even days after the seizure and manifests as behavioural changes as a result of cerebral exhaustion. In the post-ictal phase many dogs are ataxic, tired, blind and occasionally aggressive.
Clinical examination in the inter-ictal period should be normal in primary epilepsy. The presence of forebrain signs on neurological evaluation in the inter-ictal period rules-out the diagnosis of primary epilepsy. The only exception to this rule is when ischaemic brain lesions develop secondary to violent seizures. A full clinical examination (paying particular attention to cardiorespiratory system) is necessary to rule out potential underlying causes or other disease mimicking seizures.
Epilepsy may be self-limiting and many animals achieve remission (freedom from seizures) with appropriate treatment.
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