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August 1989, Volume 39, Issue 8

Original Article

EPILEPSY AND PHOTOSENSITIVITY

Hasan Aziz  ( Neurology Unit, Jinnah Postgraduate Medical Centre, Karachi, Pakistan. )
Patricia Francis  ( Neurology Unit, Jinnah Postgraduate Medical Centre, Karachi, Pakistan. )
Syed Munawar Ali  ( Neurology Unit, Jinnah Postgraduate Medical Centre, Karachi, Pakistan. )
Zaki Hasan  ( Neurology Unit, Jinnah Postgraduate Medical Centre, Karachi, Pakistan. )

Abstract

In a series of 2053 cases of epilepsy studied 3.9% were found to have some form of photosen­sitive epilepsy. The mean age of onset was 14.9 years for males, 11.8 years for females. In the age group of 6 - 10 years there was a definite male preponderance. In 48.2% cases the seizures were caused by watching television and in 7.4% they were precipitated by sunlight or electric lights. Primary generalized tonic clonic seizures were seen in 44.4 % cases and 34.6% had secondary generalized seizures. E.E.G. was normal in 60% cases, while 18.8% had nonspecific dysrhythmias, 2.1% hyper­synchronization during the interictal period with spike and sharp wave complexes. A family history of photosensitive epilepsy was present in 14.1% cases (JPMA39: 212, 1989).

INTRODUCTION

Local folidore, popular in this region has very aptly described an epileptic as being sensitive to water and it is presumed that the flash or flicker produced by light as it is reflected off the surface of the water or waves produces a flash frequency which triggers off epileptic seizure in a susceptible patient. The more modern equivalent of this phenomenon is termed Photosensitive Epilepsy, which is a form of Reflex Epilepsy where convul­sion is precipitated by visual or photic stimulus, e.g., flickering light, watching television, defective neon light, etc. Photosensitive Epilepsy was first described by Gowers1 and Radoviei et al2 were the first to recount self induced epilepsy. In 1952 Livingston3 was the first to describe television epilepsy. Studies carried out later4divided photosensitive patients into three groups i.e., those having fits when ex­posed to flickering lights in every day life; those having fits only when exposed to flickering lights during an E.E.G., and those in whom abnormal dis­charges occurred on intermittent photic stimula­tion (IPS) but without any clinical seizures.
Studies by Jeavons and Harding5,6 also divided the photosensitive patients into three groups. The most practical classification is there­fore -
1. Pure Photosensitive epilepsy: It occurs only when the susceptible patient is exposed to a flickering light or rarely to a very bright light that is not flickering. Television is the most common stimulus and most often the seizures are Tonic Clonic type.
2. Epilepsy with photosensitivity: Both spon­taneous seizures as well as those induced by every day ificker occur or there maybe spon­taneous seizures, and abnormally evoke IPS, but there is no evidence of the seizures being promoted by flickering lights in everyday life.
3. Pattern sensitive epilepsy: This is closely re­lated to photo-sensitive epilepsy. Pattern sen­sitive patients are almost always photosensi­tive and evidence shows that many photosen­sitive patients are pattern sensitive.

PATIENTS, METHODS AND RESULTS

From January 1984 to January 1986, 2053 patients were seen in the Epilepsy Clinic of neurol­ogy department. Of these, 81 patients (3.9%) had some form of photosensitive epilepsy. There were 45 males and 36 females with an overall mean age of 14.9 years, the mean age for females was 11.8 years and 17.4 for males. The youngest patient was a twelve days old male and the oldest a fiftyfour years male. Male to female ratio was equal in 0-5 years age group after which the frequency of males in­cidence increased (Table I).

Five patients (3 male, 2 female) 0-17 years age group were mentally retarded. The type of seizures were secondary generalized in 2 primary generalized (Tonic Clonic), secondary generalized, complex partial and simple partial in the remaining 3 cases. Seizures were precipitated by watching television in 38.3% cases while electric lights were responsible in 6.2%. In 48.2% cases television alongwith other provoking factors like fever or fatigue gave rise to fits. In 7.4% cases electric lights along with other precipitants resulted in seizures. Primary generalized (tonic-clonic) type of seizures were reported in 44.4% patients with photosensi­tive epilepsy, 34.6% had secondary generalized seizures whilst 3.7% had simple partial seizures and 3.7% had simple partial plus secondary seizures. Complex partial, petitmal, myoclonic, atonic and tonic seizures were less common (Table II).

Family history of epilepsy was present in 14.1% cases. Out of 81 cases with photosensitive epilepsy 48 cases bad E.E.G. done, 60.4% had normal E.E.G. tracing, 18.8% nonspecific hyper­synchronization, 2.1% hypersyncbronization with spike and wave, 2.1% were borderline abnormal E.E.G. Petitmal, diffuse slowing, nonfocal, petit­mal and myoclonic seizures, subcortical and myoclonic jerks were also seen in few cases.

DISCUSSION

The population in the country being exposed to the hot bright sun all the year round, the number of photosensitive epilepsy encountered should be much more than is obvious from the series as the flash frequencies caused by reflection of sunlight on iron girdeit, tin roofs, metal gates and steel doors is much more. The number in this study is lower than other studies carried out in the west owing to the fact that still our population is not ex­posed to extensive TV viewing as theft counter­parts in the west, moreover the number of hours spent in front of the TV very rarely exceeds more than 1-2 hours intermittently. With the advent of video-games and video cassette recorders there are spurts of watching films on the VCR for 12 to 24 hours continuously over the weekend, as this forms the only sort of entertainment for the general urban population. Owing to the reasons enumerated above, the rate of photosensitive epilepsy is low in our population. Differing also from other studies, the present study has a preponderance of males. The patients with mental retardation and photosensitive epilepsy were mostly males unlike the other studies where females were more. The explanation for this could be that at present patients with mental retardation are seen in the child guidance clinic and psychiatric clinic and self induced epilepsy was not en­countered in this studynor has impulsive attraction to the TV set been reported. The other major difference in this study is that in 66.7% of the patients, seizures occurred in combination with precipitants other than the photic stimulation, though 432% exhibited a pure form of photosensitive epilepsy caused by the TV or electric lights only.

REFERENCES

1. Goweis, W. it Epilepsy and other chronic convulsive diseases. Their causes, symptoms and treatment. New York, Wood, 1885.
2. R.adovici, A., Misirliou, V. and Gluckman, M. Epilepsy reflex provoquee par excitations optiques des rayons solaries. Rev. Neurol., 1932; 1:1305.
3. Laidlaw, J. and Richens, A. A textbook of epilepsy. 2nd ed. Edinburgh, Churchill Livingstone, 1982.
4. Bickford, it G., Daly, D. and Keith, H. M. Convulsive effects of light stimulation in children. Am. J. Dis. Child., 1953;86:170.
5. Jeavons, P. M. and Harding, G.F.A. Photosensitive epilepsy clinics in developmental medicine No. 56. Inn­don, Heinemann, 1975.

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