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 50-70 cases per 100 000 of the population (in developing countries, the figure is higher due to more primitive obstetric services and consequently the greater likelihood of cerebral infection and head trauma).

Incidence varies greatly with age, with high rates in early childhood, low levels in early 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. The second peak is now higher than the first and, indeed, old age has become the most common time in life to develop the condition.

The point prevalence of active epilepsy ranges from 0.5 to 1 percent of the population.

A seizure is a paroxysmal event due to abnormal, excessive, hypersynchronous discharges from an aggregate of central nervous system (CNS) neurons. Depending on the distribution of discharges, this abnormal CNS activity can have various manifestations, ranging from dramatic convulsive activity to experiential phenomena not readily discernible by an observer.

The meaning of the term seizure needs to be carefully distinguished from that of epilepsy.

Epilepsy describes a condition in which a person has recurrent seizures due to a chronic, underlying process. This definition implies that a person with a single seizure, or recurrent seizures due to correctable or avoidable circumstances, does not necessarily have epilepsy. Epilepsy refers to a clinical phenomenon rather than a single incident, since there are many forms and causes of epilepsy.

Determining the type of seizure that has occurred is essential for focusing the diagnostic approach on particular etiologies, selecting the appropriate therapy, and providing potentially vital information regarding prognosis.

In 1981, the International League against Epilepsy (ILAE) published a modified version of the International Classification of Epileptic Seizures that has continued to be a useful classification system (Table 1). This system is based on the clinical features of seizures and associated electroencephalographic findings.

A fundamental principle is that seizures may be either partial (synonymous with focal) or generalized. Partial seizures are those in which the seizure activity is restricted to discrete areas of the cerebral cortex. Generalized seizures involve diffuse regions of the brain simultaneously. Not all seizure types can be classified as partial or generalized. This appears to be especially true of seizures that occur in neonates and infants.

Table 1
ILAE Classification of Seizures
Partial Seizures
  • Simple partial seizures (with motor, sensory, autonomic or psychic signs)
  • Complex partial seizures
  • Partial seizures with secondary generalization
Primarily generalized seizures
  • Absence (petit mal)
  • Myoclonic
  • Clonic
  • Tonic
  • Tonic-clonic (grand mal)
  • Atonic
Unclassified seizures
  • Exemples: Neonatal seizures, Infantile spasms

Overall (all ages), nearly 60% of seizures are partial and the remaining 40% are generalized. In infancy/early childhood, a higher proportion of patients have generalized onset seizures. The proportion of partial and generalized seizures becomes equal by mid-childhood. In early adulthood, the proportion of partial and generalized seizures remains equal, but then progressively shifts toward partial seizure predominance in mid-to-late adulthood.

Seizures are an indistinct sign of neurologic disorder that can be attributed to several different causes. Being so, the qualified physician must be able to analyse all the clinical manifestations present in a given patient (partial versus generalized seizures, age at onset, family history, etc) as well as the results of the diagnostic tests and whenever possible define the specific epileptic syndrome.

The majority of people with epilepsy have a good prognosis. The prognosis is strongly influenced by the underlying cause. In many 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 antiepileptic 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).

Item 1
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