Epilepsia. 2015 May;56(5):699-706.
Prevalence and etiology of epilepsy in a Norwegian county – a population based study
Marte Syvertsen,1 Karl Otto Nakken,2 Astrid Edland,1 Gunnar Hansen,1 Morten Kristoffer Hellum,1 Jeanette Koht1
1Department of Neurology, Drammen Hospital, Norway
2National Centre for Epilepsy, Oslo University Hospital, Norway
Objective: Epilepsy represents a substantial personal and social burden worldwide. When addressing the multifaceted issues of epilepsy care, updated epidemiological studies using recent guidelines are essential. The aim of this study was to find the prevalence and causes of epilepsy in a representative Norwegian county, implementing the new guidelines and terminology suggested by the International League Against Epilepsy (ILAE). Methods: Included in the study were all patients from Buskerud County in Norway with a diagnosis of epilepsy at Drammen Hospital and the National Centre for Epilepsy at Oslo University Hospital. The study period was 1999-2014. Subjects with active epilepsy were identified through a systematic review of medical records, containing information about case history, EEG, cerebral MRI, genetic tests, blood samples, treatment and other investigations. Epilepsies were classified according to the revised terminology suggested by the ILAE in 2010. Results: In a population of 272.228 inhabitants, 1771 subjects had active epilepsy. Point prevalence on Jan. 1st 2014 was 0.65%. Of the subjects registered with a diagnostic code of epilepsy, 20% did not fulfill the ILAE criteria of the diagnosis. Epilepsy etiology was structural-metabolic in 43%, genetic/presumed genetic in 20% and unknown in 32%. Due to lack of information, etiology could not be determined in 4%. Significance: Epilepsy is a common disorder, affecting 0.65% of the subjects in this cohort. Every fifth subject registered with a diagnosis of epilepsy, was misdiagnosed. In those with a reliable epilepsy diagnosis, every third patient had an unknown etiology. Future advances in genetic research will probably lead to an increased identification of genetic and hopefully treatable causes of epilepsy.
Epilepsy is one of the most common neurological disorders, affecting about 22 million people worldwide. However, due to methodological issues, designing a reliable study of the occurrence of epilepsy is challenging. Nonetheless, this kind of knowledge is crucial in order to plan and provide sufficient health care for this very heterogeneous group of patients. Furthermore, we know that prevalence and incidence of epilepsy are strongly related to factors such as age, geography and socioeconomic status, making it important to obtain epidemiological data from different parts of the world, or even different parts within the same country.
Several methods have been used to estimate prevalence of epilepsy in different areas. Some studies have used registries of diagnostic codes. They probably overestimated the prevalence, as diagnostic codes are mainly an administrative tool and do not always represent the final conclusion of the physician. Other studies are door-to-door based and hampered by small numbers and concealment, as epilepsy still suffers from major stigma in many parts of the world. Studies based on questionnaires distributed to the entire population would be prone to selection-bias, as people suffering from the health-problem in question have a greater tendency to respond.
Figure 1: The study was conducted in Buskerud county, Norway
The Norwegian county of Buskerud (Figure 1) is particularly well suited for studying the epidemiology of epilepsy. Due to the Norwegian social welfare system, socioeconomic status and access to health care is fairly equal across the country. Buskerud has only one neurological and one pediatric ward, located at Drammen Hospital. There is only one private neurologist and two private pediatricians in the county, and they do not have access to EEG-equipment. The only EEG-laboratory in Buskerud is located at Drammen Hospital. Referring to a pediatrician or a neurologist, including an EEG, is standard procedure when diagnosing epilepsy in Norway. Thus, we hypothesized that close to all subjects with epilepsy in Buskerud county, would visit Drammen Hospital at some point.
We searched the databases of the neurological, pediatric and neurohabilitation wards and EEG laboratory at Drammen Hopsital, to identify subjects with an ICD-10 code of epilepsy (G40) in the time period of Jan 1st 1999 – Jan 1st 2014. There were more than 18 000 registered contacts in more than 2500 individuals. In addition, we performed a similar search at the National Center for Epilepsy, just outside the county-border, to identify subjects from Buskerud receiving follow-up there. The medical record of each individual was then carefully reviewed. We found that more than 500 subjects (20%) did in fact not fulfill the diagnostic criteria for epilepsy. The most common reason was an initial suspicion of epilepsy, later disclaimed by diagnostic work-up. Furthermore, 400 subjects (19%) did no longer have active epilepsy, meaning that they had been seizure-free and off medication for more than five years. This means that a substantial amount of patients actually get well. The final number of subjects with active epilepsy in Buskerud County was 1771 in a total population of 272.228. Prevalence was 0,65%. (1)
Figure 2: Etiology of epilepsy in Buskerud county
The most common cause of epilepsy in was structural-metabolic (43%) (Figure 2), meaning that the reason for developing epilepsy was a known disorder or injury, of which the most common was brain-stroke (Figure 3). 20% had a genetic or presumed genetic cause, but only 3% had an exact genetic diagnosis. In nearly one third the cause of epilepsy was unknown. This is a very high number, but it is in line with studies similar to ours. In the large group of people with an unknown cause of epilepsy, we suspect a high number of undiscovered genetic conditions. Identifying these subjects is crucial, as some genetic causes of epilepsy are treatable, i.e. glucose-1 transporter deficiency syndrome. Despite the ongoing revolution on genetic knowledge, there still seems to be a substantial translational gap between research and clinical practice. Hopefully, the group of people with an unknown cause of epilepsy will diminish in the future, contributing to improved quality of life in many and maybe even cure in a few.
Figure 3: Causes of structural-metabolic epilepsy in Buskerud county
- Syvertsen M, Nakken KO, Edland A, Hansen G, Hellum MK, Koht J 2015 Prevalence and etiology of epilepsy in a Norwegian county – A population based study. Epilepsia 56:699-706.
Acknowledgements: This study was supported by Vestre Viken Hospital Trust.
Marte Syvertsen, M.D.
Department of Neurology