Page 1 - ILAE_Lectures_2015

Chapter 1

The incidence and prevalence of epilepsy

AIDAN NELIGAN1 and J.W. SANDER2,.3

1Homerton University Hospital Foundation Trust, London, and 2UCL Institute of Neurology,
Queen Square, London and 3Epilepsy Society, Chalfont St Peter, Buckinghamshire

The incidence and prevalence of epilepsy

Epilepsy is the commonest neurological condition affecting people of all ages, race and social class.
There are an estimated 50 million people with epilepsy in the world, of whom up to 75% live in
resource-poor countries with little or no access to medical services or treatment1,2.

Early epidemiological studies in epilepsy up to the 1960s were carried out in tertiary referral centres
which favoured the belief that epilepsy was a chronic, progressive incurable condition with little
chance of remission famously expressed by Gowers writing in 1881 that ‘The spontaneous
cessation of the disease is an event too rare to be reasonably anticipated in any given case’3.

Since then many epidemiological studies have been published from both developed and resource-
poor countries but methodological differences, lack of standardised classification, problems with
case ascertainment and diagnostic accuracy have resulted in disparity in study findings, as well as
reflecting the heterogeneous nature of a diagnosis of epilepsy4.

Diagnostic accuracy is a particular problem in epilepsy as seizures are a symptom of diverse
underlying cerebral aetiologies and normally do not have any physical manifestations4.
Consequently a definitive diagnosis of epilepsy is often only made after an extended period of
follow up, as evidenced in the Rochester study5 and the National General Practice Study of Epilepsy
(NGPSE), a community-based study of epilepsy in the United Kingdom6. Moreover it has been
found that 20−30% of those attending tertiary referral centres with refractory epilepsy do not in
fact have epilepsy7, with the most common differential diagnoses being dissociative seizures and
syncope. As expected, neurologists are better at the diagnosis of epilepsy than non-specialists
(mistake rate 5.6% vs 18.9%)8, but a misdiagnosis rate of 5% should be considered as the absolute
minimum.

Many people with epilepsy may not come to medical attention, either through ignorance or lack of
awareness of the symptoms. This is particularly true of absence and minor complex partial seizures,
which may only be recognised in retrospect following presentation with a generalised seizure9.
Indeed in one study of general practices only 20% of patients with seizures suspected the diagnosis
prior to medical consultation10.

Incidence studies

While many people presenting with seizures do so with a prior history of events, between one-third
and half present with a single unprovoked seizure6,11. Most studies combine the incidence rates for