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. |
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The
diagnosis of primary idiopathic epilepsy is a diagnosis
of exclusion.
History
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
Clinical
signs
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 |
|
Vocalisation |
The
seizure activity can be divided into several phases:
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.
Image:
Golden retriever with head tilt and contralateral ptosis
and severe
depression just after a seizure - courtesy of Simon Platt, AHT.
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. |
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Epilepsy
may be self-limiting and many animals achieve remission (freedom
from seizures) with appropriate treatment.
References
Berendt
M, Gram L (1999) Epilepsy and seizure classification
in 63 dogs: A reappraisal
of veterinary epilepsy terminology. JVIM 13, 14-20.
- PubMed -
Podell
M, Fenner WR, Powers JD (1995) Seizure classification
in dogs from a non referral-based population. JAVMA 11,
1721-1728.
- PubMed -
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