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Family
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Preview of Understanding Epilepsy
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Seizures, or fits, take
many forms. They originate in the brain, and different types of seizures
arise in different parts of the brain.
The brain is involved in forming emotions, thoughts
and memories, in controlling movement, and in appreciating sensations,
sounds, smells, tastes and sight. It is divided into two halves joined
in the middle; the right half controls the left-hand side of the body
and the left half controls the right-hand side. For most of us, the
left half is ‘dominant’; in other words, it controls how
we form and understand language. Each half (or hemisphere) is further
divided into four lobes as shown in the diagram.
Damaging one part of the brain will take away its function.
For example, damage to the left occipital lobe will result in the person
being unable to see anything on the right; damage to the right frontal
lobe may cause a person to be paralysed down the left-hand side. Conversely,
activating the left occipital lobe, for instance with electrical current,
results in the person seeing coloured blobs on the right-hand side, and
stimulation over the right frontal lobe causes the left part of the body
to move.
A seizure can be likened to an electrical storm. This
storm can be confined to one part of the brain, spread to other parts
of the brain or involve the whole brain at once. Those that start in
one part of the brain are known as ‘partial seizures’ and those
that start in both halves at once are known as ‘generalised seizures’.
What is experienced depends on where in the brain the seizure starts,
and how far and how quickly it spreads.
In the next section we define the different types of
seizure in some detail.
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The brain has two hemispheres: the left and
the right. Each hemisphere is composed of four lobes. Each of
the four lobes of each cerebral hemisphere has its own particular
physical and mental functions. These can be impaired by brain
damage.
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Types of seizures
Almost all seizures are sudden, short-lived and self-limiting.
Most occur spontaneously without warning and, as explained above, the
form of the seizure depends on the part of the brain involved. The classification
is presented in the box.
| CLASSIFICATION
OF SEIZURES |
Partial
seizures
Generalised seizures |
A
B
C
A
B
C
D
E
F
|
Simple
partial seizures
Complex partial seizures
Secondary generalised seizures
Absence seizures (petit mal)
Myoclonic seizures
Clonic seizures
Tonic seizures
Tonic–clonic seizures (grand mal)
Atonic seizures |
Partial seizures
- Simple partial seizures: These are seizures
confined to one small part of the brain, during which there is no
loss of consciousness. They are often divided into temporal lobe,
frontal lobe, parietal lobe and occipital lobe seizures, depending
on where the seizure starts.
In temporal lobe seizures, the patient may experience a feeling of
intense fear, vivid memory flashbacks, intense déjà vu
(a feeling of having been in an identical situation before) and unpleasant
intense smells or tastes. We can all experience some of these from
time to time and of course they are not usually seizures; for example,
déjà
vu is a common and normal experience. The main difference is that,
with epilepsy, these things happen regularly, without reason, are
short-lived and occur with an intensity that is rare in everyday
life.
In frontal lobe seizures, there may be uncontrolled jerking of one
arm or leg or the head and eyes may turn to one side.
In parietal lobe seizures, the patient may experience tingling down
one side of the body.
In occipital lobe seizures, the patient may experience flashing lights
in one half of the vision. The seizure usually lasts a matter of
seconds.
- Complex partial seizures: These are really
the next stage up from simple partial seizures, and the clue is in
the word ‘complex’. In these, the seizure involves a larger
part of the brain and spreads to enough of the brain so that the patient
is no longer aware of his or her environment (that is, becomes unconscious).
The spread of the seizure can either be so fast that the patient does
not experience the simple partial seizure, or be slow enough for the
patient to have, for example, a feeling of déjà vu, a
strange unpleasant taste or an awareness of coloured flashing lights
lasting seconds to a few minutes be-fore becoming unaware of the surroundings.
During the seizure, it is quite common for complex, strange or inappropriate
actions to occur (called ‘automatisms’). For example, the
patient may fumble with his or her clothes or make chewing movements.
Occasionally, the actions are coordinated and can even take the form
of running, dancing, undressing or speaking nonsense. These seizures
usually last a matter of minutes, but are occasionally more prolonged.
On coming round, the patient is completely unaware of what he or she
has done.
- Secondary generalised seizures: These result
from the spread of the seizure throughout both halves of the brain;
the spread can be slow enough for the patient to have a warning (the
aura, which is in fact a simple partial seizure) or so rapid that the
patient loses consciousness without an aura. This spread is called
secondary generalisation and the seizure takes the form of a ‘generalised
tonic–clonic’ seizure. In this, the patient often goes stiff
(called the tonic phase) and may let out a high-pitched cry; he then
falls, may go blue, his arms and legs jerk rhythmically (called the
clonic phase), grunting can occur and he may foam at the mouth.
During the seizure the patient may bite his tongue or wet himself;
it usually lasts a few minutes, and afterwards the patient is often
confused, may not know where he is and will often sleep. The after-effects
(the
‘post-ictal’ phase) last for minutes or hours. This seizure,
which used to be called a ‘grand mal’ attack, is now known
as a tonic–clonic seizure, and is also sometimes referred to as
a convulsion.
Generalised seizures
These are seizures that begin in both halves of the
brain at once; as such there is no warning and consciousness is lost
immediately. Often this seizure is a tonic–clonic seizure (see above),
but it can be a clonic seizure (no stiff phase) or a tonic seizure (no
shaking stage, the patient just falls like a board). There is also a
rare type in which the patient just slumps to the ground, but recovers
quite quickly (an atonic seizure).
There are also two other categories of generalised seizures: absences
and myoclonic jerks.
- Absences: These used to be called a ‘petit
mal’ attack. They are short blank spells, usually in children,
that last just a matter of seconds and can be confused with poor
attention or loss of concentration. Children with absence epilepsy
can have hundreds of these in a day and often neither the child nor
observers are aware of most of them because they are so brief. They
are associated with a particular brain wave pattern that is discussed
in the next chapter.
- Myoclonic seizures: These are usually
seen in patients with other seizure types, and are very brief jerks
of one limb or the whole body. The patient may describe suddenly
dropping a cup of tea as his hand flings up, or his whole body being
thrown to the ground.
From this, it can be seen that there are many different types of seizure
and you are probably already aware that there are other conditions
that can be mistaken for a seizure and these are discussed in the next
chapter.
The brain is divided into two halves (hemispheres) joined
in the middle. The right half (hemisphere) of the brain controls
the left-hand side of the body and the left half controls the
right-hand side
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What causes seizures?
All brain activity depends on the passage of electrical
signals. The brain consists of millions of cells called neurons which
have bodies and long arms with branches known as axons. It is down these
axons that the electrical signals pass, like a telephone signal down
a telephone line. When the signal reaches the end of the axon, it causes
the release of a chemical; this chemical communicates with a nearby neuron
body via special ‘receivers’ called receptors. They may ‘excite’
this neuron body and, if the excitation is sufficient, then a further
signal is sent (or ‘fired’) down its axon. This is the way
in which the neurons communicate with each other. If only excitation
took place in the brain, then eventually all the neurons would be firing
together, so causing an ‘electrical storm’ such as seen in
a seizure. But some neurons release a chemical from their axons that
inhibits the surrounding neurons, stopping them from ‘firing’.
The brain functions properly when there is a balance between the excitation
and the inhibition. If there is either too much excitation or too little
inhibition in a part of the brain (an imbalance), a seizure results.
In partial seizures, the local imbalance between excitation
and inhibition can be caused by local damage to the brain – for
instance, from lack of oxygen at birth, meningitis or head injuries – or
by abnormal tissue such as a brain tumour or a defect in brain development.
In some cases, the reasons for the partial seizures are not always known.
In generalised seizures, the chemical imbalance affects
a wide area of brain, and the brain often shows no obviously abnormal
structures. This can be caused by drugs, alterations of the body chemistry,
excessive alcohol, or inherited or unknown factors. Thus epileptic seizures
are a symptom of an underlying brain disturbance in the same way that
stomachache is a symptom of an underlying gut disturbance (for example,
food poisoning, ulcers, appendicitis, etc.).
What is epilepsy?
Epilepsy is defined as a condition in which the person
is prone to recurrent epileptic seizures, so diagnosis is a measure of
the probability of having epileptic seizures. If you have one seizure
brought on by excessive alcohol, and then you become teetotal, the chances
of having another seizure are very small and you would not be diagnosed
as having epilepsy. If, on the other hand, you had a number of seizures
because of a damaged part of your brain, the chances of having another
seizure are very high; you would be diagnosed as having epilepsy.
The decision about whether a patient does or does not
have epilepsy is not always clear cut. We all have a lifetime chance
of having a seizure of about 1 in 30 (29 to 1 against for those who bet,
that is, ‘an outside chance’), and we can considerably increase
our chances of having a seizure by drinking excessively or taking certain
drugs. Most doctors diagnose patients as having epilepsy only if they
have two seizures within a year, because, in this instance, the chances
of having a third seizure are probably over 80 per cent (4 to 1 on, that
is, ‘a sure thing’).
The difficulty arises in patients who have had one
seizure, and in this instance the doctor usually assesses the chances
of another seizure, aided and abetted by various investigations, and
by knowledge of the type of seizure and the probable cause. Most doctors
in the UK would not usually treat one single seizure because of the low
odds of having another seizure (less than 50/50) and the possible side
effects of medication.
The second difficult question is, if a patient is diagnosed
as having epilepsy, how many seizure-free years must pass before he or
she is no longer thought to have epilepsy? Unfortunately, there is no
simple answer to this question, but it is certainly true that most people
with epilepsy eventually stop having seizures and thus should not be
registered as having epilepsy (if someone has not had a headache for
10 years, it would be perverse to call him or her a headache sufferer).
It is important to bear in mind that epilepsy is a
symptom and not a disease as such. A symptom is something experienced
by patients, indicative of an underlying disease. This is the case with
epilepsy, which should be considered as an indicator of some underlying
brain problem. A wide spectrum of brain conditions can result in epilepsy.
The orange
traces of this electroencephalograph (EEG) show the electrical
activity
in the brain during an epileptic seizure. During an epileptic seizure,
a chaotic
and unregulated electrical discharge passes through the brain,
causing an increase
in activity. |
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What is an epilepsy syndrome?
A syndrome is a medical term referring to a specific
condition in which characteristic groups of symptoms occur together.
They are often named after the person who first described them. For example,
West’s syndrome consists of infantile spasms (epileptic attacks
in which the baby suddenly flexes or stiffens) with a particular brain
wave pattern and often mental handicap in babies aged between three and
twelve months. Most go on to have epilepsy that is difficult to treat
and a learning disorder. This explains what occurs and what happens,
but does not tell us the underlying cause of the seizures (there are,
in fact, a multitude of causes of West’s syndrome).
The most common epilepsy syndromes are benign childhood
epilepsy with centrotemporal spikes (this is a term that refers to the
distinctive EEG changes) and primary generalised or generalised epilepsies.
The box outlines the features that characterise these two epilepsy syndromes.
Electrical
signals are carried along a nerve cell via its axon. For a signal
to cross the synapse (gap) between two nerve cells, chemical
neurotransmitters must pass from the synaptic knob to receptor
cells on the next cell. |
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| FEATURES
OF EPILEPTIC SYNDROMES |
| The two most commonly
found types of epilepsy syndrome are benign childhood epilepsy
and primary generalised epilepsy. |
Epileptic
syndrome
|
Features |
| Benign
childhood epilepsy with centrotemporal spikes |
- Occurs between 2 and 14 years
- Can be inherited
- Seizures involve face, throat
and tongue, and conscious-
ness is preserved
- Occasionally tonic–clonic
seizures occur during sleep
- Typical EEG pattern
- Most get completely better
and drug treatment is not
usually necessary
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| Primary generalised epilepsy |
- Usually occurs in childhood
or adolescence
- Can be divided into many
different subtypes
- Can be inherited
- Seizure types consist of a
combination of absences,
tonic–clonic seizures and
myoclonic seizures
- Seizures usually occur on, or
within a couple of hours of,
waking
- Typical EEG pattern
- Usually well controlled with
valproate
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KEY POINTS
- Seizures in different parts of the brain produce
different effects
- Seizures take many forms and can be likened to
electrical storms in the brain
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