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CURRENT DATA ON THE INCIDENCE AND PREVALENCE OF EPILEPSIES IN CHILD AND ADOLESCENT

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Autor: Catrinel Iliescu
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ABSTRACT: 

The aim of this paper is to review the research results in recent years in terms of current data related to the incidence and prevalenceof epilepsies. Discussions refer to the correct definitions of terms and fi gures are detailed. The incidence and prevalence data proved to be extremely consistent and homogenous in several European areas. Using a calculation model derived from these data which was previously used in literature on Europe population, this paper also discusses the possible spectrum of epilepsiesin Romania, using the population census from 1st of July 2007.

 

 

1. INTRODUCTION

Knowing the causes, frequency and natural history of a certain disease (in our paper, the epilepsy in children and adolescents) contributes to improving healthcare. One can thus determine the extent of the problem, optimal therapeutic approach may be suggested, and treatment effectiveness may be assessed. Sometimes methods to preventthe disease or its complications may be defined. One can determine the costs (social, personal), considered to behigh for epilepsy due to its relatively high frequency, andto the fact that it is a chronic disease.

In this paper I propose to synthesize research results in recent years in terms of current data on the incidence and prevalence of epilepsies and to discuss the possible epilepsy incidence and prevalence figures in our country. In this overview I will not discuss other, equally important, epidemiological aspects of epilepsies, which relate to a etiology, comorbidity, prognosis and mortality, which will be explored in another paper.

 

2. DEFINITIONS OF TERMS

The study of a particular disease can not be achieved without a consistent definition of terms, so that concepts like epilepsy, seizures, acute symptomatic seizures,febrile seizures have in principle well stated definitions (Figure 1). These terms have been established by consensus by the Epidemiology and Prognosis Committee of ILAE (International League against Epilepsy), in1993, with this aim in mind, namely to provide a common language in epidemiological studies.

To classify the types of seizures and epileptic syndromes,the 1981, and respectively 1989 classifications are still valid today, starting from the precise knowledge of terms, too7,8,9 (Figure 2).

The precise meaning of epidemiologic terms as well as of other useful terms for epilepsy must be known13, keeping in mind that since there is no consistency among the epileptic syndromes, we do not talk about epilepsy, but about epilepsies (Figure 3).

Currently epidemiological studies are using improved methods that are based on the principle of anaccurate and clear definition of the studied condition.

Epidemiological studies of incidence are considered to be the most useful. Their disadvantage consists in their high costs and in the fact they are difficult toachieve, so there are actually few studies relating to the total population; in particular, the incidence data allow specialists to assess the healthcare needs in the population. Therefore, a prevalence study is more often achieved, which is easier, but it has the disadvantage of bringing in inconclusive or even erroneous information,too.

A recent article by the team of Forsgren and colleagues14,published in 2005 showed that epidemiological studies related to epilepsy have been made in Britain, western Mediterranean countries, the Balticand Nordic countries. Many European countries have not made epidemiological studies, and, in fact it is probable that they are not absolutely necessary since the data can be extrapolated to neighbouring countries with similar living conditions. However, it is important to note that about large parts of Europe there are no epidemiological data, and included here are the Eastern Europe (excluding Baltic countries) and Eastern Mediterranean countries. In the analysis performed by the above-mentioned team, data from Russia, Belarusand Ukraine were excluded because the populationis very large in number and the epidemiological data is very inconclusive and probably incorrect (the prevalence data from Russia contain figures with very low values, probably underestimating the true prevalence of epilepsy in these areas).

 

 

 

3. INCIDENCE

Incidence quantifies the number of new events or cases of disease occurring in a population of individuals at risk in a given period of time. There are two types of measuring incidence, namelythe rate of incidence and cumulative incidence.

The incidence rate (incidence) of epilepsy refers to the number of newly diagnosed patients with at least two unprovoked seizures in one year, per 100,000 people.

Cumulative incidence is the proportion of people who fall ill in a certain period of time. It is, in fact, a sum of incidence values by age, and provides an estimate of the probability or risk of an individual to fall ill in a certain period of time. Since mortality is higher among people with epilepsy, but in a modest proportion compared to the general population, the cumulative incidence can provide an estimate of the proportion of the total population that was affected by epilepsy by a certain age.

 

3.1. LARGE POPULATION STUDIES

Incidence studies in large population groups are much fewer compared to those on prevalence. To provide as accurate information as possible on probable etiological factors such studies should be prospective, that is why they are often time consuming and expensive14 .

The article by Forsgren and collaborators14 mentioned earlier, pointed out that, in Europe, 12 incidence studies have been conducted covering the northern and western parts of Europe.

European studies covering all age groups were conducted in Faeroe Islands (The Netherlands) – 1986,Bordeaux (France) – 1990, Iceland – 1996, Switzerland- 1997, United Kingdom – 2000.

They showed an annual incidence rate of between 43 and 47 per 100,000 inhabitants. There are some differences due to the inclusion in some studies of a first unprovoked seizure.

There are studies showing that only about 50% of the total cases of epilepsy have their onset in childhoodor adolescence 18.28.

The incidence of epilepsy in children has been estimated in various populations of children over the last 70 years, but using different methods for the definition of cases, including the age range – there is a great heterogeneity among them and among the conditions studied: epilepsy, first unprovoked seizure, acute symptomatic seizures.

Studies that have examined the incidence of epilepsy in children and adolescents have been conducted in Europe (Finland, United Kingdom, Germany, Italy,Iceland, Norway, Spain, Sweden, and Switzerland),USA (Rochester, MN, Houston TX), Canada (NovaScotia, New Haven), and Guam (Mariana Islands).

In spite of methodological differences, the incidencein studies from Western industrialized countriesis remarkably consistent in different geographical areas, particularly if results of the last two decades are taken into account.

Average annual incidence rate of unprovoked, recurrent seizures, per 100,000 children, according to studies, recorded a minimum of 35.0 in Turku, Finland14 and 41.0 in Nova Scotia (Nova Scotia) 5 and amaximum of 82.3 in Northern Sweden 4.

Two recent prospective studies of incidence of epilepsy in children aged from 1 month to 15 years conductedin Germany15 and Spain’s Navarra region12 have demonstrated an annual rate of age-related incidence of 60.7 and 62.6 per 100,000 respectively.

There have been studies that have reported higher values of incidence, but they also included the study of the first seizure and / or of acute symptomatic seizures 6.32.

 

3.2. AGE, GENDER ANDETHNICITY / RACE

3.2.1. Age: There are a number of studies that report the incidence of epilepsy in specific age groups.The assessment of these studies also requires careful analysis of the terms used. The highest incidence is recorded in the first months of life, it decreases dramatically after the first year, it seems relatively stable over the first decade of life and decreases again in adolescence18; since the first year of life, the incidence rates are maximal in the first month, according to the prospective study conducted by Sidenvall et al 33 – 318per 100,000; the incidence rates for different age levels, according to a study published in 2001 by Freitag and colleagues15, are: 145.8 per 100,000 – between 1 month- <12 months, 62.1 per 100,000 – between 1 – <5 years,49.7 per 100,000 – between 5 years – <10 years, 55.9per 100,000 – less than 10 years – <15 years.

3.2.2. Genus: Most studies that examine the gender of the participants showed a discreetly higher proportion of boys18,21,24,33, noting that these differences vary with age1.18: up to age 5 incidence rates are higher with 30 -60% in girls; after the age of 5 years incidence rates are higher with 10-20% in boys.

The study conducted by Freitag et al.15 does not point out a statistical difference between boys and girls, on any age level. Differences, when they are noted, in the incidence rates between the genders might be related to: the predominant types of seizures/ syndromes in a certain age group, possibly reflecting, in fact, the different susceptibility of girls and boys at certain ages, the difference in exposure to different risk factors because of social and cultural differences and possible gender variations in diagnosis.

3.2.3. Race / ethnicity: most large population studies have been conducted on white race groups of European descent; Asian and African studies were also homogeneous in terms of race, thus racial differences have been analyzed only in studies of incidence or cohort of children within the frame of the National Collaborative Perinatal Project 27, where the incidence of a febrile seizures was not different among racial groups up to the age of 7 years.

 

3.3. TYPES OF SEIZURES

The proportion of certain types of seizures is highlighted in several contemporary studies on incidence, which used existing classification of epileptic seizures proposed by the International League Against Epilepsy(ILAE) in 1981.

Studies of incidence from Rochester, Minnesota18Faeroe Islands25 and Chile22 showed a discretely higher proportion of d is 50% of focal onset seizures. Approximately half of the cases with focal onset seizures were secondary generalization.

Studies in developing countries report a higher incidence of cases with generalized onset seizures (remains to verify whether it is a correct observation or due to classification errors in studies of Third World countries).

The results, when using consistent criteria, lead to the figure of 60% of cases in favour of partial seizures.

 

3.4. EPILEPTIC SYNDROMES

Difficulties in syndromologic classification lead to questions about the usefulness syndromologic classification in epidemiological studies, an opinion which I strongly disagree with– on the contrary I think that, precise syndrome classification will contribute toa better understanding of epilepsy and of its impacton those affected.

From the data of the recent prospective studies on incidence (both including children aged between 1month and <15 years, with newly diagnosed epilepsy, i.e. at least two unprovoked seizures, at least 24 hours apart) the data from Table 1 below should be mentioned.

 

3.5. SOCIO-ECONOMIC STATUS

Socio-economic status (SES) describes the distributionof income, education, occupation and socialclass. There are few studies detailing the relationship between socio-economic status and epilepsy. Their results are sometimes discrepant and do not alwaysmake it clear whether low socioeconomic status is a risk factor or a consequence of epilepsy.

A population-based control-case study conducted in Iceland19 showed that a relationship exists between low SES and epilepsy in adults but not children.

 

3.6. TRENDS OVER TIME

Information on the evolution in time of the incidence of epilepsies is given by studies from Copparo, Italy16 and Rochester, Minnesota18 – Figure 4.

In the Italian study, the incidence of epilepsy hada decreasing trend from 1964 – 1978, although thereis the possibility that these results should be related to the methodology used.

In Sweden the incidence of epilepsy in childrenin 1986 (88/100.000) was lower than in 1976(134/100.000)4.33. The diff erence could be partly explainedby the possible inclusion in older studies of non-epileptic episodes; however there is a clear decrease in the incidence of epilepsy in children in industrialized countries. The decrease of the incidence of epilepsy in children over time can not be clearly explained by current clinical or epidemiological data and warrants further research.

Unlike the situation encountered in children, it seems that the incidence of epilepsy in the elderly population is increasing – this at least in the UnitedStates. This situation could be explained, at least in part, by the growth of the population with a history o fstroke2 (although the incidence of stroke is decreasing,its prevalence is increasing due to higher survival rate after cerebral stroke).

 

3.7. CUMULATIVE INCIDENCE

Estimates on the cumulative incidence data were provided by three studies on population 18,22,29: in Denmark22, the risk of epilepsy until the age of 80 years was 1.3%, a figure significantly lower compared with the study of Rochester Minnesota18, which estimated the cumulative incidence at 4% for epilepsy and more than 5% for all unprovoked seizures; in this study the cumulative incidence of epilepsy and unprovoked seizures issignificantly higher for males compared to females.

 

 

The difference between Denmark and Rochester studiescould be explained by the significantly higher incidence of epilepsy in the elderly in the case of Rochester study.The study conducted in Iceland29 had the following results in terms of cumulative incidence: 1.9% until theage of 55 years, 3.6% by the age of 75 years, 4.5% by the age of 85 years, thus we can estimate that about 1 person in 25 will have epilepsy at some point in life.

With respect to children, the cumulative incidencerates before the age of 15 are approximately 0.9%, accordingto a study published by Freitag and colleagues15 and 1%, according to the Icelandic study29.

 

4. PREVALENCE

The prevalence quantifies the proportion of individuals in a population who have the disease at some point and provides an estimate of the probability(risk) for an individual to be sick at some point intime13. Unlike incidence, prevalence is easier to calculate and therefore there are more prevalence studies in different populations, and the data are useful incertain situations (Figure 5).

Prevalence is a measure of the interaction of factors such as incidence, mortality and disease remission,and except for some isolated areas (such as Iceland)prevalence is affected by factors such as migration of the population and access to medical care.

Prevalence is more a reflection of survival and disease severity or chronicity than of its frequency. In fact, the prevalence measures what is left of the incidence data after people are lost through mortality or remission.

Prevalence refers to the number of epilepsy patients with active epilepsy at a time, per 1000 people.

Difficulties of interpreting prevalence data come also from inconsistencies in defining epilepsies, although the data are improved due to ILAE recommendations concerning epidemiological studies.

 

4.1. OVERALL PREVALENCE

Estimates of the prevalence of epilepsy in industrialized countries is between 3.3 and 7.8‰ (average5.2‰), according to the synthesis made by Forsgren et al 14, although the prevalence may be higher in selected population groups.

Prevalence is higher in developing countries, in some studies going beyond the 4% – although the data are sometimes difficult to interpret, because many times details about the adjusted prevalence by age group are not provided.

Data on the prevalence of epilepsy in childrenhave shown values between 4-5‰ (0.4 – 0.5%), withan average of 4.3‰6,10,11,117,34

 

4.2. AGE, GENDER AND ETHNICITY /RACE

4.2.1. Age: Studies from developed countries reported a low prevalence in childhood and a tendency to increase with age. Prevalence rates are approximately 2-3‰ in the age group up to 7 years and 4-6‰ in the age group 11-15 years11. Significantly different results are given by studies from developing countries, where prevalence is higher in childhood and few cases are recorded after the age of 40 years (it has been suggested that these results are due to possible high mortality of people with epilepsy in the developing countries, but it remains to be determined whether this is perfectly true); it is generally estimated that the prevalence of epilepsy in the countries of South America and Africais 10-15‰30.31, one reason being the difference in parasitic infections responsible for epileptic seizures.

4.2.2. Genre: In agreement with the results of incidence studies, most of the prevalence studies reported a male predominance.

4.2.3. Race / Ethnicity: higher prevalence rates were generally reported in African-American children compared with white people, but these differences ares mall11..

 

4.3. TYPES OF SEIZURES ANDEPILEPTIC SYNDROMES

It is normal to have differences between the distribution of the types of seizures and, in particular of epileptic syndromes according to the type of studies -incidence or prevalence. In studies of prevalence, data may be different due to the intervention of several factors such as mortality in different groups, the type and severity of epilepsy syndrome, which will modify the data of prevalence and the likelihood of remission.

 

4.4. TRENDS IN TIME

Prevalence data provided by the Rochester18 studycovers the period from 1940 to 1980 and thus allow assessment of trends in epilepsy over time, as follows: slight decline in prevalence rates in the age group between birth and nine years, these data being consistent with results of studies of incidence in the same age group; a slight increase for the same data in the age group 10-14 years. The problem of Rochester study is related to the structure of the population – relatively small and homogeneous, and therefore the data might not be widely applicable.

 

 

5. PEOPLE WITH EPILEPSY INROMANIA

How many people are there in Europe with active epilepsy ? – it is a question that the members of Forsgren’steam have asked14. If one is talking about an average prevalence of 5.2 cases per 1,000 persons, all age categories being included here but taking into account the fact that the identification of cases may never be complete,it is estimated that approximately 6 in 1000 Europeans have active epilepsy. It is likely that these data arecorrect, being consistent with the prevalence data from the United States of America (6.8 per 1000, reported by Hauser et al. 17in 1991) and Australia (7.5 per 1000,reported by Beran et al. in 1985, quoted by Forsgren14).

Then, the above-mentioned authors have developed a model that helped them calculate the number of new cases and patients with active epilepsy in Europe by age categories (children and adolescents,people with active working age, seniors), from data obtained first of all from studies conducted in the last decade, which proved sufficiently homogeneous interms of their results (Table 2).

 

Table 2. The data used for modelling the incidence and prevalence of epilepsy in Europe (note: these figures are higher than those  resulting from studies, taking into account the fact that perhaps not all cases are recorded).

 

I consider that this model is logical and reasonable to be applied in Romania, too, because probably from both the genetic point of view and from that of the environmental conditions which might influence the frequency of epilepsies, Romanian population did not prove to be too different from other European nations. I might be criticized for this opinion. Obviously, a prospective study of incidence would be the most correct solution, but not a realistic one taking into consideration the current funding and organization of the medical system. It seems very unlikely that incidence of epilepsy in a geographical area representative for Romania could be studied at this moment due also to the un-homogeneous addressability of patientsto medical specialists. In these circumstances I believe, once again, that this model could be considered a basis for an absolute reasonable calculation.

I have used the data from the National Institute of Statistics 20, according to which Romania’s total populationon 1 July 2007 was about 21.54 million inhabitants. Below are the results obtained with the proposed model, which are then summarized in Table 3.

Table 3. Estimates of the incidence and prevalence of epilepsy in Romania, using a model calculation based on extrapolations of data from recent European studies.

 

At a 6‰ prevalence, the number of people with active epilepsy reaches approximately 129,000 in Romania.The situation in age groups may possibly be as follows:the population of children and adolescents (0-19 years)in Romania is about 4.83 million people. Taking into account the prevalence data by age group of children and adolescents, 4.5 – 5‰, it results a figure of about 23,000 children and adolescents with active epilepsy inRomania. The population with working age (20-64years) in Romania is 13.50 million. At 6‰ prevalencein this age group, we obtain the figure of about 81,000 people aged 20-64 years with active epilepsy in Romania. Elderly population (over 65) in Romania is about 3.2 million people. Applying a prevalence figure of 7‰, which seems to be the most correct, one can get a total of 22,400 active seniors with epilepsy. The total number of persons with active epilepsy in Romania calculated after the above model is approximately 126,400, afigure close to that obtained by the calculus that used the average prevalence.

In conclusion, by both methods of calculation onemay arrive at a figure of about 126,400 to 129,000 (anaverage of about 128,000) of people with active epilepsy in Romania. Of these, approximately 18.2% in our country are children and adolescents, 64.1% are active adults and 17.7% are elderly people.

Taking into account the data of incidence in allage groups, it should also be known that it is unlikely that all new cases were recorded, even in highly developed countries, much less in Romania.

The average annual incidence in Europe is estimated to be 50-55 per 100,000 people. The probable annual number of new cases in Romania is thus about11,310.

Given the incidence by age, then in children and adolescents, with an incidence rate of 70 per 100,000,there will be approximately 3400 new cases annually.In adults aged 20-64 years, with an incidence rate of 30 per 100,000 people, will be approximately 4050n ew cases annually. In persons older than 65 years,with an incidence rate of 100 per 100,000 people, there will be a number of 3,200 new cases annually.

Combining the figures resulting from the incidence data on adjusted according to age- we arrive at a figure of about 10,650 new cases annually in Romania.

In conclusion, considering the incidence data by both methods of calculation, one arrives at a figure of about 10,650 to 11,310 (average 11,000) new cases of epilepsy each year in Romania. According to these calculations, in Romania, children and adolescents represent 32% of new cases, adults 38%, while people older than 65 years represent 30%.

 

6. CONCLUSIONS

Epilepsy is one of the important causes of neurological morbidity. Annual incidence rates in developed countries are 40-47 per 100,000, higher in children and the elderly, and the rate of prevalence for active epilepsy is an average of 5.2%, also with variations according to age group. But it is likely that the studies fail to include all people with epilepsy, and therefore actual figures may be higher. In addition top revalence, studies include those with active epilepsy but not those who had epilepsy at some point and are in remission for more than five years.

As a trend over time, there is now evidence of adecrease in the incidence of epilepsy in certain age groups.

Modelled data from representative studies in specialist literature to fit the Romanian population, suggest that in our country data could be as follows: approximately 11,000 new cases of newly diagnosed epilepsy annually, of which 3,400 are children and adolescents, and about 128,000 people with active epilepsy,of which 23,000 are children and adolescents.

 

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Correspondence to:
Catrinel Iliescu “Al. Obregia” Hospital, Pediatric Neurology Clinic, Bucharest e-mail: iliescu_catrinel@yahoo.com

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