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Photosensitive epilepsy

Photosensitive epilepsy is a form of epilepsy in which seizures are triggered by flickering light or other visual stimuli, such as bold or moving patterns. Of those who suffer from epileptic seizures, between 3% and 5% are known to be of the photosensitive type (approximately two people per 10,000 of the general population). Often they have no other history of epilepsy. Females are more commonly affected than males, and there is distinct genetic correlation. more...

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In affected people, the symptoms usually first occur during childhood or adolescence and few people develop them after the age of 20. Sufferers generally learn to avoid the stimuli that trigger seizures and in many cases, the symptoms subside with time. There is no cure, although effective medication is available in appropriate cases.

Sensitivity is increased by alcohol consumption, sleep deprivation, and other forms of stress.

The response varies with the individual and can be any type of epileptic seizure, with characteristics ranging from a disconcerting loss of awareness to alarming fits. The seizure may be preceded by a period of disorientation sufficiently lengthy for the subject to take avoiding action, which may be simply to look away from the stimulus if possible, or to cover one eye so that fewer nerve cells are subjected to the stimulus.

Stimuli

Vulnerable people can be induced into seizure by any flickering light, such as from stroboscopic lamps in discotheques and faulty fluorescent lamps. The frequencies most likely to induce a seizure are between 15 Hz and 25 Hz (i.e. between 15 and 25 times per second), but some people are susceptible to frequencies as low as 3 Hz or as high as 50 Hz.

Travelling along tree-lined avenues with the sun flashing between the tree trunks can be a trigger, as can the flickering of sunlight among the leaves of trees as they move in the wind, or the reflection of light from the surface of rippling water.

Flashing light is not the only trigger and in some cases, looking at certain geometric patterns such as bold stripes or chequers can cause a seizure, or looking between railings while walking, or watching a rhythmically moving object such as a moving staircase.

Images displayed by some computer games can also trigger seizures, which is a particular hazard for affected children.

Television screens

Apart from the nature of any image displayed on a television screen, the way in which the screen functions can serve as a trigger. In particular, PAL, one of the colour encoding systems used in broadcast television (the standard in the UK), refreshes at an interlaced frame rate of 25 Hz (half the mains frequency) and is a known cause of seizures. In most circumstances, television screens are viewed from a distance such that the refresh is indiscernible, but with the trend towards larger television screens, the problem becomes more evident.

The triggering effect of a flickering light is greatly increased with the contrast it produces, and it is more likely to induce a seizure in an otherwise dark room compared to one with bright ambient lighting. So, watching television from a reasonable distance and in a well-lit room greatly reduces the likelihood of seizure.

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The teenager with epilepsy has special needs - Editorial
From British Medical Journal, 10/10/98 by Philip E.M. Smith

Even for healthy teenagers, coping with emerging adulthood is a major challenge. A chronic disability such as epilepsy simply magnifies the problems of adolescence, and the penalties for seizures at this time are far more severe than in childhood. Epilepsy and its treatment have a direct bearing on major aspects of lifestyle such as education and employment prospects, driving ability, the use of alcohol and recreational drugs, relationships, contraception, pregnancy, and parenthood. Self consciousness is paramount and deviations from peer group norms assume great importance: epilepsy can be disastrous for an adolescent's self esteem and sense of identity.

Adolescents with epilepsy are often caught between paediatric and adult medical disciplines, with neither service specifically addressing their needs. The Liverpool group advocates multidisciplinary consultations with a neurologist, paediatric neurologist, and specialist epilepsy nurse.[1] Whatever the setting, the consultation must focus on the needs and independence of the teenager, with the parents taking a back seat. If possible, part of the consultation should be with the teenager alone: an opportunity arises while examining the patient in a separate cubicle.

The same principles of clinical management apply in adolescence as in any age group, but for the teenager the problems are more pressing and the long term consequences of mismanagement more serious.[2] A correct diagnosis of blackouts is essential. The diagnostic process in teenage epilepsy must take account of three situations. Firstly, some epilepsies, such as juvenile myoclonic epilepsy, present in adolescence and carry specific implications for management.[3] Secondly, some childhood onset epilepsies, such as benign childhood epilepsy with centrotemporal spikes, consistently remit in adolescence.[4] Thirdly, common conditions such as vasovagal syncope, psychogenic non-epileptic attack disorder, and migraine often present first in teenagers and may mimic epilepsy.

Optimal seizure control is central to managing epilepsy. When anti-epileptic drugs are indicated the ideal is to prescribe the lowest effective dose of a preparation with as few side effects as possible, given as a once or twice daily dose. A vigorous approach to seizure control is justified since interventions often have progressively less impact as epilepsy and its consequences become established. Surgery for epilepsy is much underused but potentially curative in some patients with localisation related epilepsies. The argument for surgery in children and adolescents is not just that it is effective[5]; it can also prevent the social, educational, and developmental handicaps which, once established, may persist even with good control of seizures.

Compliance with drug treatment is a particular problem in adolescence. As at any age, the reasons include denial of epilepsy, concern over side effects, and complacency about good seizure control. For teenagers there is also an intense peer pressure to conform--their tablets a reminder with each dose that they are different--as well as rebellion against parental involvement in the management of their epilepsy. Side effects are extremely important at this age since even mild cognitive dysfunction may permanently harm education and employment prospects. Cosmetic effects limit the usefulness of certain antiepileptic drugs (such as phenytoin) in young people.

Several lifestyle issues merit discussion. Young women taking enzyme inducing antiepileptic drugs must be warned about potential failure of oral contraceptives. More importantly, all women of childbearing age taking antiepileptic drugs need to know of their possible teratogenicity. There is some evidence that folate reduces this risk for enzyme inducing medications[6] and valproate.[7] Given that at least 30% of teenage pregnancies are unplanned, a pharmacological dose of folate 5 mg daily seems a sensible addition to any antiepileptic regimen.

Advice on regular sleep is particularly important in idiopathic generalised epilepsy, the commonest form in teenagers. Complete abstinence from alcohol is unnecessary, but teenagers must recognise its potential for interacting with drugs and impairing sleep quality and so provoking seizures. The influence of recreactional drugs on epilepsy is unknown. The risk of exposure to computer screens and flashing lights often concerns patients and parents. Photosensitive epilepsies may present in the teenage years, but such exposure is harmless to most teenagers; a baseline electroencephalogram is helpful in refining this advice. A discussion of sudden unexpected death in epilepsy is sometimes appropriate and is touched on in a helpful patient information booklet.[8]

Epilepsy affects educational and employment prospects, with career choices being inevitably restricted by the diagnosis.[9] Further restrictions imposed by parents, suggested by peers, or initiated by the patient are sometimes inappropriate. Such restrictions can threaten independence, deny opportunities for friendship, and encourage social isolation. A common sense approach is needed towards leisure and sports activities, both patient and parents often having to accept living with a degree of risk. The problems faced by teenagers with epilepsy apply, often to a lesser extent, across the range of patients with epilepsy. As we improve our services for this vulnerable group, the lessons learnt can only benefit people with epilepsy as a whole.

Philip E M Smith Consultant neurologist

Epilepsy Unit, University Hospital of Wales, Heath Park, Cardiff CF4 4XW

[1] Appleton RE, Chadwick DW, Sweeny A. Managing the teenager with epilepsy: paediatric to adult care. Seizure 1997;6:27-30.

[2] Besag FM. Modern management of epilepsy: adolescents. Bailliere's Clin Neurol 1996;5:803-20.

[3] Timmings PL, Richens A. Juvenile myoclonic epilepsy. BMJ 1992;305:4-5.

[4] Kurtz Z, Tookey P, Ross E. Epilepsy in young people: 23 year follow up of the British national child development study. BMJ 1998;316:339-42.

[5] Ventureyra EC, Higgins MJ. Complications of epilepsy surgery in children and adolescents. Pediatr Neurosurg 1993; 19:40-56.

[6] Biale Y, Lewanthal M. Effect of folic acid supplementation on congenital malformations due to anticonvulsant drugs. Eur J Obstet Gynaecol Reprod Biol 1984 ;18:211-6.

[7] Elmazar MMA, Thiel R, Nau H. Effect of supplementation with folinic acid, vitamin [B.sub.6] and vitamin [B.sub.12] on valproic acid induced teratogenesis in mice. Fundamental and Applied Toxicology 1992;18:389-94.

[8] Preston J. Epilepsy and the young adult. London: Epilepsy and the Young Adult, 1996.

[9] Thompson P, Oxley J. Social aspects of epilepsy. In: Laidlaw J, Richens A, Chadwick DW, eds. A textbook of epilepsy. 4th ed. Edinburgh: Churchill Livingstone, 1993:661-704.

BMJ 1998;317:960-1

COPYRIGHT 1998 British Medical Association
COPYRIGHT 2000 Gale Group

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