There are several different types of seizure. Classification is important because different seizures have differing underlying causes, and often respond to specific medications:

Partial(focal) seizures

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A partial seizure that develops into a generalised seizure is referred to as a secondarily generalised seizure, at which point convulsions and loss of consciousness occur.

The most frequent type of partial seizure is the so-called complex-partial seizure. This is often called a temporal lobe seizure, since the temporal lobe is the commonest site for these seizures to arise. However, complex partial seizures can arise from any part of the brain. Patients typically experience a strange feeling or odd smell (the aura) followed soon afterwards by an alteration of consciousness. This causes mental clouding and a "spaced out" manner. In general, patients will not respond to commands and may manifest unusual behaviors such as picking at their clothing, smacking their lips or wandering in a purposeless manner. Unconsciousness, convulsions and collapse do not occur.

A less common type of partial seizure is the simple partial seizure. Here, seizure activity is restricted to a region of the brain that controls movement or receives sensation, producing restricted jerking of a limb (simple motor seizure), or an abnormal feeling. Occasionally, persistent weakness of the limbs may follow such a seizure. The person remains conscious and aware of his or her surroundings, and is able to communicate with others.

Generalised seizures

Generalised tonic-clonic seizures, previously termed "grand mal" seizures, are the most dramatic and frightening kind of seizure. Sudden collapse with loss of consciousness is followed by muscle spasm ("tonic") and violent jerking ("clonic") of the limbs that builds to a climax and then subsides and stops on its own after several minutes. The involuntary contraction of muscles can cause tongue biting, temporary arrest of breathing, and incontinence. Injury may occur in falling to the ground and as a result of the violent movements of the limbs. Exhaustion, muscle aches and headache are common for several hours after the seizure has settled, in the so-called "post-ictal" period.

Absence seizures ("petit mal") also involve loss of consciousness, and as such are also generalised seizures, but are quite distinct from tonic-clonic convulsions. Seen most frequently in children, absences involve very brief periods (seconds) of "blanking out" that may occur many times a day, and are often put down to daydreaming. These staring spells briefly interrupt whatever the child is doing and may be associated with fidgeting or picking at clothes (automatisms). The child and his or her family may be quite unaware of anything unusual, and absence seizures frequently only come to light when schoolwork suffers.

Other varieties of generalised seizure may involve sudden loss of muscle tone with collapse or large-scale jerks of the whole body, but these are rare.

Reviewed by Dr Andrew Rose-Innes, MD, Department of Neurology, Yale University School of Medicine, New Haven.

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