Epilepsy
Around 50 million people in the world have epilepsy. It is the most common serious neurological condition, with an annual incidence in developed countries of 50 cases per 100,000 of population (in developing countries, the figure is higher due to less advanced maternal and child care conditions, and consequently the greater likelihood of cerebral infection and head trauma).
An epileptic seizure is a clinical event characterised by the manifestation of transient signs and/or symptoms which stem from abnormally excessive or synchronous activity of neurons in the brain. Depending on the location and distribution of the abnormal electrical activity in the central nervous system, the person with epilepsy can have various motor, psychic, sensory and autonomic clinical manifestations. The intensity of the clinical manifestations is variable because a seizure can have a generalised tonic-clonic presentation ('intense convulsive activity') which carries a high emotional burden, or sometimes a presentation characterised by subjective phenomena (only perceived by the patient).
Epilepsy is a clinical condition characterised by a long-lasting predisposition to developing epileptic seizures and by the neurobiological, cognitive, psychological and social consequences of this pathology.
Epilepsy is a brain disease defined by the following conditions:
1) at least two unprovoked (spontaneous) epileptic seizures separated by a period of more than 24 hours;
2) one unprovoked seizure and a probability of further seizures similar to the recurrence risk (at least 60%) after two unprovoked seizures, occurring over the next 10 years;
3) diagnosis of an epilepsy syndrome.
Thus, a person with a history of one (or several) seizure(s) in the context of a modifiable precipitating event (or cause) does not necessarily have epilepsy. Epilepsy is a clinical phenomenon and should not be understood as a single disease, since there are many manifestations and causes of epilepsy.
Determining the type of seizure that has occurred is essential for focusing the diagnostic approach on particular aetiologies, selecting the appropriate therapy, and providing potentially vital information regarding prognosis.
Focal onset seizures are those in which the abnormal electrical activity is propagated in a localised area of the cerebral cortex. Generalised seizures have a simultaneous onset in both cerebral hemispheres. Some seizures are difficult to classify, and are thus considered to be seizures of unknown onset.
Incidence varies greatly with age, with high rates in early childhood, low levels in adult life, and a second peak in people over 65 years old. In recent years, despite the fact that global incidence has remained nearly constant, there has been a fall in the number of affected children accompanied by a sharp rise in epilepsy in the elderly, making the second peak now higher than the first one. The point prevalence of active epilepsy ranges from 0.5 to 1 percent of the population.
ILAE 2017 Operational classification of seizure types
Adapted from Fisher RS, et al. Instruction manual for the ILAE 2017 operational classification of seizure types. Epilepsia. 2017 Apr; 58(4):531-542.
Overall, nearly 60% of seizures are focal onset and the remaining 40% are generalised onset. In infancy/early childhood, a higher proportion of patients have generalised onset seizures. The proportion of focal and generalised onset seizures becomes equal by mid-childhood to early adulthood. With increasing age, the proportion progressively shifts toward focal onset seizure predominance.
Seizures are the manifestation of neurological disorder that can be attributed to several different neurological diseases. As such, the qualified physician must be able to frame all the clinical manifestations present in a given patient (such as the type and semiology of seizures, age at onset, family history, etc.) as well as the results of diagnostic tests (EEG, NMR, among others) and whenever possible define the specific epileptic syndrome.
The majority of people with epilepsy have a good prognosis. Prognosis is strongly influenced by the underlying cause. In some people, particularly children, the condition will remit, although a substantial proportion will have epilepsy all their lives. Overall, 60-70% of patients become seizure free after treatment with anti-epileptic drugs (figure 1), and some patients can remain in remission after subsequent drug withdrawal. The other 30-40% continue to have seizures with varying degrees of frequency and severity (refractory epilepsy).
Figure 1 Seizure free patients in response to antiepileptic drug treatment.
Source: adapted from Brodie MJ, Kwan P, Schachter SC. Fast Facts: Epilepsy. 3rd edition. Oxford (UK): Health Press Limited; 2005
Bibliography
1. Epilepsy: Key Facts. Available at: https://www.who.int/news-room/fact-sheets/detail/epilepsy [accessed 2019.11.21]
2. Pimentel, José, and Carla Bentes. Epilepsia : conceitos, diagnóstico e tratamento. Lisbon: Lidel, 2016. Print.
3. Fisher RS, et al. ILAE official report: a practical clinical definition of epilepsy. Epilepsia. 2014 Apr;55(4):475-82.
4. Fisher RS, et al. Epileptic seizures and epilepsy: definitions proposed by the International League Against Epilepsy (ILAE) and the International Bureau for Epilepsy (IBE). Epilepsia. 2005 Apr;46(4):470-2.
5. Fisher RS, et al. ILAE official report: a practical clinical definition of epilepsy. Epilepsia. 2014 Apr;55(4):475-82.
6. Fisher RS, et al. Instruction manual for the ILAE 2017 operational classification of seizure types. Epilepsia. 2017 Apr;58(4):531-542.