Posts tagged: Epilepsy

EPILEPSY: THE FACTS-CAUSES OF FEBRILE CONVULSIONS

The cause of a febrile convulsion, is, as the name implies, a fever or high temperature. Any of the common childhood infections such as chickenpox, tonsillitis, upper respiratory, ear, bowel or urinary infections may cause a high temperature and therefore cause a febrile convulsion. It is unclear whether it is how quickly the temperature rises, or how high it eventually gets which determines whether a convulsion will occur. Lots of children between 6 months and 5 years of age have febrile illnesses but obviously the majority will not have a convulsion. One of the reasons why some children do, and others do not have convulsions with fever, is because of inherited factors which are important in determining whether febrile convulsions will occur. Almost one third of children will be found to have a family history of febrile convulsions in their parents or siblings (brothers and sisters). When one parent has a history of febrile convulsions, the risk to a child of developing a febrile convulsion is almost 20 per cent; if both parents have a history, then the risk is increased to 50 per cent. The brothers and sisters of a child who has had a febrile convulsion have a three times increased risk of having a febrile convulsion themselves; this risk is even higher in identical twins.

Most children who have febrile convulsions do not need any tests. Usually the cause of the infection and of the fever is obvious from the examination carried out by the doctor—for example, a sore throat (tonsillitis), red ear (otitis media), rash (for example, chickenpox), or cold and cough. Rarely, however, and particularly in children under 18 months of age, a convulsion may be the first sign of meningitis or encephalitis (group (c) above). If there is any doubt as to whether a child has meningitis (particularly in children aged 6-18 months), then a lumbar puncture must be done, and other tests may well be required. Children with simple febrile convulsions do not need to have an EEG or brain scan. However, children with complex febrile convulsions (group (b)) may well need them in order to explore what is the underlying cause of their asymmetrical or prolonged convulsion, or earlier slow development.

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THE FIRST SEIZURE AND THE DIAGNOSIS OF EPILEPSY

A common story is for parents to be woken by the stertorous breathing or grunting of a child in the next bedroom. They go to him, thinking usually that he is having a bad dream, and find him staring, unresponsive, convulsing, and perhaps blue. Few if any parents can cope calmly with such a scene. It is usual for the family doctor to be telephoned at once, and, if there is any delay in his arrival, for an ambulance to be summoned as well. Many parents subsequently confess that they thought their child was dying, so they are acting in an entirely rational way. Almost invariably, however, by the time the family doctor or ambulance has arrived, the seizure is over, the child is sleeping peacefully, and the adults are making tea. But they will not sleep again that night. Many—though not all—are immediately aware of the nature of what they have just seen.

Although the first seizure can occur anywhere and at any time, another common scenario is for the first seizure to occur in a young woman in the company of her friends or at work. In this case, the lack of ready access to the family doctor, whose name and telephone number is unlikely to be known to the bystanders, results in an ambulance being almost invariably called, and the unfortunate young woman being rushed off to hospital. She will recover consciousness either in the ambulance or in the Accident and Emergency Department of the hospital. To the confusion invariably consequent to the generalized seizure must be added the feeling of ‘What on earth has happened to me, and how have I finished up here on a stretcher with strangers peering at me?’ Obviously, therefore, although ambulance services are rather prickly on this point, a friend should accompany her to hospital—not only to provide moral support when recovery of consciousness occurs but also to give an accurate account of events to the hospital staff. In this case, the diagnosis of a tonic-clonic seizure is clear, but in others matters are not so straightforward. It is important to distinguish between an epileptic seizure and some other event which may initially seem to be one. Patients may speak in terms of a ‘black-out’, ‘funny turn’, or ‘blank spell’, and we have to do our best to analyse the cause.

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THE CAUSES OF EPILEPSY: TUMOURS

A tumour arising within the brain understandably causes great anxiety-perhaps more so than with tumours elsewhere in the body, as a brain tumour may appear to strike at the very centre of one’s soul and being. Many people with simple headaches due to anxiety or stress believe that they have a brain tumour which is causing their headache. However, the incidence of primary tumour is very low (10 per 100 000 per year). It is, however, true that tumours can cause epilepsy. This is much more likely to happen in adults than in children.

Brain tumours are either primary or secondary. A secondary tumour is one that has been carried in the blood to the brain from another site. Cancers of the lung (bronchus) or breast are by far the most common of these. Usually the site of the original cancer is known, and the appearance of seizures in such a patient is an ominous sign indicating that a secondary tumour has arisen within the brain. Sometimes, however, the original cancer has not been discovered at the time of the first seizure, and a careful clinical examination will reveal a small tell-tale lump in the breast, or the lung cancer will be seen on a chest X-ray.

Primary tumours of the brain do not arise in nerve cells. They either arise in the supporting cells between nerve cells which play an active role in their nutrition (glial cells) or in the meninges, the covering membranes of the brain. These tumours are called gliomas and meningiomas. There are other types of primary cerebral tumours, such as those arising from the cells lining the cavities of the brain, or from blood vessels, but these are rare.

Primary brain tumours are not like cancer of the breast, or bowel, or bronchus. They show no tendency to develop blood-borne secondary deposits in other organs. This is fortunate, but there are other characteristics which hinder effective treatment. The gliomas infiltrate normal brain extensively, so there is no apparent margin beyond which one can be quite certain that no abnormal cells have reached. This makes recurrence after surgical excision very likely. Meningiomas, however, are encapsulated tumours, and can often be removed completely, with a good chance of complete eradication. However, meningiomas often have an extensive blood supply, so complete removal may be technically very difficult.

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THE CAUSES OF EPILEPSY: ANOXIA

Anoxia means lack of sufficient oxygen, an essential component of the normal ongoing chemistry of the cell. Cerebral nerve cells are amongst the highest consumers of oxygen in the body, as reflected in the fact that a quarter of all arterial blood goes to the brain. If the oxygen supply is cut off, then damage to nerve cells occurs after a few minutes. Some die, but others are damaged in such a way that they may paroxysm ally discharge in subsequent life.

Anoxia may occur at birth. During each uterine contraction in a prolonged labour the fetal heart rate slows, and the supply of oxygenated blood to the brain is reduced. The umbilical cord may become tightly wound around the baby’s neck. The placenta may separate prematurely. After birth, for a variety of reasons, the child may not breathe for a few minutes. These are four examples of how anoxic brain damage can occur at birth. If severe, the brain damage results in severe learning difficulties, cerebral palsy, or epilepsy. However, as has already been mentioned, the cause of these three is often due to antenatal factors rather than problems with the birth itself.

Anoxia also occurs in febrile convulsions, as has already been discussed. During a seizure the oxygen requirements of brain nerve cells are enormously increased, and yet the resulting convulsion interferes with normal respiration, so that the blood leaving the lungs picks up insufficient oxygen. The combination of excessive demand and inadequate supply may on rare occasions result in anoxic damage to cerebral nerve cells. The nerve cells which seem most susceptible to damage, at the age at which febrile convulsions occur, are in the temporal lobe.

A stroke is usually due to an obstruction to an arterial vessel to one particular part of the brain, so nerve cells in the territory supplied by the blocked vessel either die as a result of lack of oxygen, or become damaged in such a way that they may form a focus for paroxysmal discharges later. Most strokes occur in late adult life, and cerebrovascular disease accounts for much of the epilepsy beginning in old age. Occasionally, however, a stroke may occur in a young adult or even in a child.

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THE DIFFERENT TYPES OF EPILEPTIC SEIZURE: TYPICAL ABSENCES

(PETIT MAL SEIZURES)

Although a translation of petit mal is the ‘little illness’, petit mal does not mean the same as ‘minor epilepsy’ as there are all sorts of small attacks which are not attacks of petit mal. True petit mal seizures, or typical absences are, by definition, associated with a characteristic EEG discharge. Short-lived partial seizures arising from a focus of abnormal nerve cells in one temporal lobe of the brain may be somewhat similar on clinical grounds, but the distinction is worth making because of the difference in cause, treatment, and outcome between the two.

Absence epilepsy is virtually invariably a disorder of childhood. A typical attack is very brief, lasting only a few seconds. The onset and termination are abrupt. The child will suddenly cease what she is doing, stare, look a little pale, perhaps flutter her eyelids, and drop her head slightly forwards. Posture of the limbs and trunk is usually maintained so she does not fall. After the seizure, the child resumes what she has been doing. Because the interruption of the normal stream of consciousness is so brief, attacks may be unobserved by parents, and not remarked upon by the affected children. One of us has seen a typical attack in a supermarket. A girl aged about nine was helping her mother unload a wire basket at the checkout. She suddenly paused, with a pot of honey held in the air between basket and counter, fluttered her eyelids, and then continued transferring the purchase without further pause.

Whereas one would be unfortunate to have more then one grand mal seizure in a day, absence seizures may be very frequent—10 to 50 seizures a day being occasionally encountered. Fortunately most children have far fewer attacks.

Absence seizures are often associated with myoclonic jerks, which are particularly frequent soon after waking. These are brief shock-like contractions of the muscles, which are so

short-lived it is not really possible to tell whether consciousness is disturbed or not. We have heard this described by one family as ‘the flying saucer syndrome’ in reference to the broken crockery that may occur as a result of jerks at breakfast-time!

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