Epilepsy and its various types

Epilepsy and cause of loss of consciousness

A seizure is a convulsion or transient abnormal event resulting from a paroxysmal discharge of cerebral event resulting from a paroxysmal discharge of cerebral neurons.

Epilepsy is the continuing tendency to have such seizures ,even if a long interval separates attacks. A generalized convulsion (i.e, a grand mal fit) is the most common recognized event.

Epilepsy is common. Over 2% of the population have two or more seizures during their lives and in 0.5% epilepsy is an active problem.

In a typical UK general practice the incidence is 46/100 000/year; approximately 65people suffer their first seizure each day.

Often no clear cause is found for seizures with onset in adult life; sometimes (through unusually) epilepsy is caused by a brain tumour or follows a stroke.

Around 250 000 people take anticonvulsant drugs, the mainstay of treatment. Neurosurgery (temporal lobectomy) is also valuable in selected cases. Neurological disease

Mechanisms

Spread of electrical activity between cortical neurones is normally restricted. Synchronous discharge of neurones in normal brain takes place in restricted groups whose limited discharges are responsible for the normal EEG rhythms.

During a seizure, large groups of neurones are activated repetitively and hypersynchronously. There is failure of inhibitory synaptic contact between neurones. This causes EEG high – voltage spike and wave activity, the electrophysiological hallmark of epilepsy.

A partial seizure is epileptic activity confined to one area of cortex with a recognizable clinical pattern .This activity either remain focal or spreads to generate epileptic activity in both hemispheres and thus a generalized seizure.

This spread is called secondary generalization of the partial seizure. The focal onset of a seizure may not clinically evident. This means that an apparent tonics clonic seizure may be either a generalized major convulsion or a tonic clonic seizure with began as a partial seizure but with out clinical evidence of its focal origin.

An area of brain is or becomes epileptogenic either because neurones have a predisposition to be hyper excitable, for example following abnormal migration patterns in utero, or because they acquire this tendency. Trauma or brain neoplasms are examples of acquired conditions that alter the seizure threshold of neurones.

Seizure threshold

Each individual has a threshold for seizure activity. Experimentally some chemicals(e.g. pentylenetetrazol, a toxic gas) induced seizure in all subjects. Individuals who are more in response to various stimuli, for example flashing lights, are said to have low seizure thresholds. This is a concept, not a measurement.

The commoner types of epilepsy

Abridged from international league against epilepsy

1. Generalized seizure types

(A) Absence seizures

(a) Typical absences with 3 Hz spike-and-wave discharge (petit mal)

(b) Atypical absences with other EEG changes

(B) Myoclonic seizures

(C) Tonic-clonic seizures (grand mal, major convulsion)

(D) Tonic seizures

(E) Akinetic seizure

2 Partial seizure types

These start by activation of a group of neurones in one part of one hemisphere,. They are also called ‘focal seizures’.

(A) Simple partial seizure (no impairment of consciousness)
(e.g. jacksonian seizures)

(B) Complex partial seizure (impairment of consciousness)

(c) Apparent generalized tonic-clonic seizures, with EEG but notclinical evidence of focal onset.

3 Unclassifiable seizures

Seizures which do not fit in one of he above categories

| Classifications of Epilepsy / Seizure | Symptoms, investigations and management process involved in epilepsy | Understanding Epilepsy Syndromes |

What is Epilepsy and what are the various types of Epilepsy