Hughlings Jackson, reputed to be the ''father'' of the modern concept of epilepsy, defined epilepsy about 100 years ago as ''an episodic disorder of the nervous system arising from the excessively synchronous and sustained discharge of a group of neurons''. Such a definition implies that, in addition to the seizure, there are disturbances in both motor and cognitive function. Hughlings Jackson also noted that a single seizure is not indicative of epilepsy, but he did not exclude seizures that are secondary to systemic metabolic disorders - such seizures would not be included in the classification of epilepsy today. The main importance of this definition is that it emphasized for the first time that epilepsy has a neuropathological basis and suggested that excitatory and inhibitory neurotransmitter processes are probably involved in the causation of the symptoms.

The term ''epilepsy'' applies to a group of disorders that are characterized by sudden and transient episodes (seizures) of motor (convulsions), sensory, autonomous or psychic origin. The seizures are usually correlated with abnormal and excessive discharges in the brain and can be visualized on the electroencephalogram (EEG).

The epilepsies are estimated to affect 20-40 million individuals worldwide and are more common in children than in adults. They are classified into two broad groups: primary or idiopathic epilepsy is the term applied to those types for which no specific cause can be identified, and secondary or symptomatic epilepsy arises when the symptoms are associated with trauma, neoplasm, infection, cerebrovascular disease or some other physically induced lesion of the brain. Seizures that accompany severe metabolic disturbances are not classified as epilepsy.

For the purpose of drug treatment, the epilepsies are classified according to the seizure type. The classification generally used is based on that proposed by the Commission on Classification and Terminology of the International League against Epilepsy. The main groups are:

Fundamentals of Psychopharmacology. Third Edition. By Brian E. Leonard © 2003 John Wiley & Sons, Ltd. ISBN 0 471 52178 7

1. Partial (focal) seizures, or seizures initiated locally in the brain. These include:

(a) Simple partial seizures, which encompass focal motor attacks and seizures with somatosensory signs or psychic symptoms.

(b) Complex partial seizures, including temporal lobe or psychomotor seizures where consciousness is impaired; these may begin as simple partial seizures.

(c) Secondary generalized seizures, which commence as (a) or (b) but later develop into generalized tonic-clonic, clonic or tonic seizures.

2. Generalized seizures, including bilateral symmetrical seizures or seizures without local onset. This group includes:

(a) Clonic, tonic and tonic-clonic seizures

(b) Myoclonic seizures.

(c) Absence and atypical absence seizures.

(d) Atonic seizures.

This classification does not take into account the frequency, duration or causes of precipitation of the seizure. Any type of attack that is maintained for more than 1 hour is termed status epilepticus, which may be qualified as focal or generalized.

The changes in the cortical EEG of patients with different types of epilepsy are illustrated in Figures 12.1, 12.2 and 12.3.

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