Dr Steve White, Consultant in Neurophysiology, St Mary’s Hospital, London
An epileptic seizure (or fit) occurs when groups of brain cells (neurones) fire
off together in a synchronized way, different from their normal, more restrained
pattern. This increased activity can produce an ‘electrical storm’,
as it spreads to involve other areas of the brain. Normally, control mechanisms
in the brain prevent this abnormal spread of activity and stop the brain cells getting
out of hand, but in a seizure these mechanisms fail. There are many factors which
can make brain cells electrically irritable and liable to fire off in this kind
of abnormal synchronised fashion, or which interfere with the usual control mechanisms
to stop abnormal rapid spread of activity.
Encephalitis may disturb these control mechanisms and produce electrical irritability
in the brain, causing seizures. Seizures are common during the initial stages of
encephalitis, when people are typically quite unwell in hospital. Because they are
occurring as a symptom of an acute illness, these are referred to as ‘acute
symptomatic seizures.’ In some instances, they can be quite difficult to bring
under control and may need a period in the intensive care unit.
Seizures may also occur at a later stage, well after the acute illness is over.
This is because the after effects of the inflammation of the brain in encephalitis
may leave the brain cells liable in the long term to producing the bursts of abnormal
synchronized activity which cause seizures. When seizures occur in the absence of
a precipitating factor (such as the acute infection), they are known as ‘unprovoked
seizures.’ Epilepsy is defined as a liability to experience recurrent unprovoked
seizures. Many patients who go on to develop epilepsy after encephalitis will have
had seizures during their acute illness and continue to have unprovoked seizures
subsequently. They have evolved from acute symptomatic seizures to epilepsy without
any period of freedom from seizures in between. However, others may not have had
seizures at all during the acute illness or may have had some seizures which settled,
but then go on to have unprovoked seizures (epilepsy) at a later stage after the
encephalitis. Although this most commonly occurs within the first year or two after
the encephalitis, seizures may begin much later in some people.
The cumulative risk for later unprovoked seizures for people who had seizures during
the initial acute encephalitis is about 10% at 5 years and 22% by 20 years. If there
were no early seizures, the 20 year risk of unprovoked seizures is around 10%. The
risk of developing epilepsy will depend on the type of encephalitis. Some varieties
– such as herpes encephalitis – are more likely to be followed by epilepsy
than others.
Seizures may be classified into different types, according to the pattern of the
abnormal electrical activity in the brain. In generalized seizures, essentially
the whole of the brain is rapidly involved right from the beginning. In focal seizures,
the abnormal electrical activity begins in one localized area of the brain. As the
seizure evolves, it may either remain in that area or spread to involve other nearby
areas on the same side of the brain (regional spread), or it may spread more widely
to involve both sides of the brain (secondarily generalized seizure). Most people
who develop epilepsy after encephalitis have focal or secondarily generalized seizures.
Because encephalitis is commonly a diffuse process involving both sides of the brain,
seizures may sometimes arise from several different locations and this is referred
to as multifocal epilepsy.
What happens during a seizure will depend on where the abnormal activity begins
in the brain and where it spreads, since activation of different parts of the brain
will produce very different effects. These will be related to what that area of
the brain does when it is functioning normally. Focal epilepsy is often classified
according to the region or lobe of the brain where the abnormal electrical activity
starts at the beginning of the seizure. So it is common to refer to frontal lobe
epilepsy, temporal lobe epilepsy, parietal lobe epilepsy and occipital lobe epilepsy,
when the seizures have their origin in those particular lobes of the brain.
Some seizures are very subtle and may just involve, for example, odd sensations
in one limb or some slight jerking of the limb. In mild seizures of this kind, there
may not be any disturbance of consciousness and people may remain fully aware of
what is happening around them, still perfectly able to speak and interact. However,
seizures will more often involve partial or complete disruption of awareness of
the surroundings. In its milder forms, this may just lead to a brief interruption
in activity with a rather blank look, a period of confusion and a failure to respond.
Although there have been recent changes in the nomenclature for different types
of seizures, the term simple partial seizure is still widely used for focal seizures
which do not involve any disturbance of consciousness and complex partial seizure
if awareness is disturbed.
Where seizure activity spreads in the brain, there may be a sequence of events as
different areas become involved. Temporal lobe seizures, for example, may begin
with a warning or aura (such as a sudden, unexplained feeling of fear or anxiety,
butterflies in the stomach or nausea), alerting the person to an imminent seizure.
There may then be a loss of awareness with blank staring and an interruption of
whatever they were doing. There may be some chewing movements and fumbling with
the clothes or other objects (automatisms). The seizure may then fade away after
a couple of minutes, often to be followed by a period of residual confusion and
tiredness. However, if the seizure activity continues to spread more widely in the
brain (secondary generalization) the initial stage may progress to a convulsion
with loss of consciousness, falling to the ground and jerking of the limbs (generalized
tonic-clonic seizure, grand mal seizure).
Although a convulsion will be quickly recognized as a seizure, it may be less straightforward
to diagnose some of the more subtle types of seizure. The diagnosis of epilepsy
depends mainly on getting a very clear account of what happens during the attack
from both the person themselves and an eyewitness who has seen a typical attack.
An MRI scan will often be done to look for local areas of abnormality in the brain,
which could be a potential source of seizures. An EEG may be carried out, recording
the electrical activity of the brain through small metal disc electrodes placed
on the scalp. In between seizures in people with epilepsy, there may be characteristic
abnormalities in the EEG (spikes and sharp waves), representing the resting activity
of groups of brain cells which are electrically irritable and which from time to
time may produce the kind of abnormal synchronized activity which leads to a seizure.
Where there is more difficulty in confirming that events are seizures or uncertainty
about the type of seizure, EEG videotelemetry may be useful. This involves simultaneous
recording of the EEG and video, usually over a period of several days as an inpatient
in hospital. The aim is to try and record one or more of the typical attacks. This
enables the doctors to look very closely at what happens during the attack and at
what is happening in the EEG at the same time. In most seizures, there will be clear
changes in the EEG with characteristic brain wave patterns, confirming that they
are indeed epileptic seizures. The EEG recording during focal seizures may also
give information about where they originate in the brain. Although videotelemetry
is still mainly based in specialist neurological centres, it is gradually becoming
more widely available.
Epilepsy is treated with medication (referred to as ‘anti-epileptic drugs’
or ‘anticonvulsants.’). A range of different tablets and capsules is
available for the treatment of epilepsy, so that there is scope for selecting the
one which best suits an individual and which gives the best possible control of
the seizures. As with medicines for other conditions, different tablets may suit
different people and work best for them, so there may be an initial stage of trial
and error, while the most suitable medicine for any particular person is identified.
The goal of treatment is to achieve the best possible control of the seizures, while
at the same time avoiding unacceptable side effects from the medication. Beginning
or adjusting anti-epileptic medication is usually done in a hospital neurology clinic.
Increasingly, specialist Epilepsy Clinics are being established around the country,
to look after the specific needs of people with epilepsy. Once anti-epileptic medicines
have been started, the dose is usually built up gradually over a period of weeks
or months, until the optimum dose for a particular individual is identified. It
is important to take the medication regularly, to minimize the likelihood of seizures
occurring. Also, abruptly stopping the medication may provoke seizures (withdrawal
seizures). If the medicines need to be stopped or changed, the dose is usually reduced
slowly, in gradual steps.
Epilepsy is a common condition world wide and many people take anti-epileptic medication
with good results over many years. Some people will go into remission and the seizures
will stop. If someone has been free of seizures for a number of years, the question
of coming off the medication may arise. Some people are able to stop the medication
and remain seizure free. Unfortunately, in others the seizures return when the medication
is withdrawn and they will need to go back on it. The decision about whether to
try coming off medication if there have been no seizures for several years is very
much an individual one, which will depend on personal circumstances and what the
consequences would be if seizures returned (for example, for someone who has got
their driving licence back or who is working). A number of factors can help predict
the risk for a particular individual of seizures recurring if medication is withdrawn
after a period of seizure freedom, so that the doctors in the neurology or Epilepsy
Clinic will be able to give some guidance to people in making this decision. The
decision should always be made after taking medical advice. If the decision is made
to come off the drugs, as emphasized, they need to be tapered off slowly over a
period of weeks or months, to avoid withdrawal seizures. It is important for medication
to be tapered under medical supervision with guidance about how to proceed and appropriate
support during the process of gradually reducing the medicine, as well as a clear
contingency plan for what to do if seizures recur as the medication is reduced.
Useful addresses
Epilepsy Action
New Anstey House, Gate Way Drive, Yeadon, Leeds LS19 7XY
Tel 0113 210 8800 Fax 0113 391 0300 Helpline 0808 800 5050
helpline@epilepsy.org.uk
www.epilepsy.org.uk
The National Society for Epilepsy
Chesham Lane, Chalfont St Peter, Bucks SL9 0RJ
Tel 01 494 601 300 Fax 01 494 871 927 Helpline 01 494 601 400
www.epilepsynse.org.uk
The David Lewis Centre
Mill Lane, Warford, Nr Alderley Edge, Cheshire SK9 7UD
Tel 01 565 640 000 Fax: 01565 640100
enquiries@davidlewis.org.uk
www.davidlewis.org.uk
The National Centre for Young People with Epilepsy
St Pier’s Lane, Lingfield, Surrey RH7 6PW
Tel 01342 832 243
info@ncype.org.uk www.ncype.org.uk
Epilepsy Scotland
Helpline: 0808 800 2200
enquiries@epilepsyscotland.org.uk
www.epilepsyscotland.org.uk
Quarriers Epilepsy Assessment Unit
Hunter House, Quarriers Upper Village, Bridge of Weir, PA11 3SX Scotland
Tel: 01505 616006 Fax: 01505 613906
hunterhouse@quarriers.org.uk
www.quarriers.org.uk
Last modified: January 2009