Elsevier

The Lancet Neurology

Volume 4, Issue 10, October 2005, Pages 627-634
The Lancet Neurology

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Incidence of unprovoked seizures and epilepsy in Iceland and assessment of the epilepsy syndrome classification: a prospective study

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Summary

Background

No population-based incidence studies of epilepsy have studied syndrome classification from the outset. We prospectively studied the incidence of a single unprovoked seizure and epilepsy in the population of Iceland, and applied the syndrome classification endorsed by the International League Against Epilepsy to this population.

Methods

We used a nationwide surveillance system to prospectively identify all residents of Iceland who presented with a first diagnosis of a single unprovoked seizure or epilepsy between December 1995 and February 1999. All cases were classified by seizure type, cause or risk factors, and epilepsy syndrome.

Results

The mean annual incidence of first unprovoked seizures was 56·8 per 100 000 person-years, 23·5 per 100 000 person-years for single unprovoked seizures, and 33·3 per 100 000 person-years for epilepsy (recurrent unprovoked seizures). Incidence was similar in males and females. Partial seizures occurred in 40% and a putative cause was identified in 33%. Age-specific incidence was highest in the first year of life (130 per 100 000 person-years) and in those 65 years and older (110·5 per 100 000 person-years). Using strict diagnostic criteria for epilepsy syndromes, 58% of cases fell into non-informative categories. Idiopathic epilepsy syndromes were identified in 14% of all cases.

Interpretation

Findings are consistent with incidence studies from developed countries. Although the epilepsy syndrome classification might be useful in tertiary epilepsy centers, it has limited practicality in population studies and for use by general neurologists.

Introduction

The epilepsy syndrome classification proposed by the International League Against Epilepsy is now in its third revision.1, 2, 3, 4 The classification uses a combination of seizure semiology, family history, clinical neurophysiology, and clinical characteristics to classify patients. Classification aims to facilitate communication between physicians, to provide consistency in scientific studies and therapeutic trials, to inform patients about their prognosis, and to aid targeted drug therapy. The use of the syndrome classification by professionals who do not specialise in epilepsy, as well as by epilepsy researchers and for epidemiological studies, has been encouraged,2 but identifying criteria are complex and the information needed is commonly unavailable to the practising clinician. Additionally, there is a lack of evidence-based criteria for individual syndromes. As a result, the syndrome classification has yet to receive wide acceptance in the general medical community.

A separate classification system has been recommended for use in epidemiological studies.5 In this system, cases are categorised on four independent axes: provoked versus unprovoked seizure, seizure type, aetiology, and number of episodes (single versus recurrent). The categorisation allows some determination of initial treatment strategies and prognosis.

No population-based incidence studies of epilepsy have included syndrome classification, in addition to more traditional categorisation by seizure type and aetiology, from the outset.5 Total population incidence studies of epilepsy have either retrospectively assigned the syndrome classification6, 7 or have reported only syndrome classification without providing other data generally used in epidemiological studies.8

We used the medical care system in Iceland to establish a nationwide surveillance system to prospectively identify all individuals who presented with first diagnosis of a single unprovoked seizure or first diagnosis of epilepsy during a 39 month period. All cases were classified by number of episodes, seizure type, cause or risk factors, and epilepsy syndrome.

Section snippets

Patients

Index cases were all residents of Iceland who were first diagnosed with an unprovoked seizure or epilepsy between December 1, 1995, and February 28, 1999. Epilepsy was defined in accordance with the 1993 International League Against Epilepsy criteria for epidemiological studies as recurrent unprovoked seizures (seizures occurring more than 24 h apart).5 In patients with newly diagnosed epilepsy, the first seizure might have occurred months or years before the study; these patients were included

Results

501 patients met the inclusion criteria during the study period. 207 of these patients had a first, single, unprovoked seizure, and 294 had a first diagnosis of epilepsy. At least one electroencephalograph was done in 444 (89%) patients studied, and at least one CT or MRI study was done in 428 (85%) patients. Inpatient video-monitoring was available in Iceland but was not done on any cases in the first year after diagnosis. The mean number of patients with unprovoked seizures identified per

Discussion

The incidence of all unprovoked seizures, epilepsy, and single unprovoked seizures, age-adjusted to the Standard European million population, of 55·2 per 100 000 person years was similar to the overall incidence reported in other total population studies in more developed countries.8, 5, 14, 15, 16, 17, 18, 19, 20 A retrospective cohort study from Rochester, MN, USA, that used the same definitions as this study found the incidence of all unprovoked seizures to be 63 per 100 000 and the

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    Dr G Gudmundsson died in May, 1999

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