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THE DIFFERENT TYPES OF EPILEPTIC SEIZURE: PARTIAL SEIZURES

Tuesday, April 28th, 2009

The exact internal perception or external manifestations of partial seizures depend upon the site of origin of discharge of abnormal nerve cells. If these lie in the part of the brain called the motor cortex, a strip of brain concerned with movement, the initial manifestation will be a contraction of muscles in the opposite side of the body, as, through evolutionary events that are not entirely clear, one side of the brain controls the opposite side of the body. Cells in the motor cortex which supply the index finger and thumb, the corner of the mouth, or the big toe are most likely to be those in which a seizure discharge begins. There are more cells assigned to controlling these muscles, which are concerned with the fine tuning of manual skills and facial expression. Statistically, therefore, there is a greater chance of abnormal events occurring in these cells, but also experiments show that they are particularly easy to excite. The first evidence of such a partial seizure may be twitching of one corner of the mouth. As the seizure discharge spreads, the muscles around the eyes are next involved, as nerve cells supplying these muscles are next door to those supplying the mouth. Next involved are the hand muscles, and next the foot muscles. This march of events was described in the last century independently by Bravais, a French neurologist, and by Hughlings Jackson, an English neurologist whose wife had such attacks. This type of seizure is therefore often called a Jacksonian seizure. It may occur with no disturbance of consciousness whatsoever, as the discharge remains confined to the motor cortex. Partial seizures in which there is no disturbance of consciousness are said to be simple partial seizures.

Another type of partial seizure with movement is known as a versive (turning) seizure. In this the head and eyes turn to one side.

Usually the arm on the side to which they are turned is elevated and twitches. Sometimes the ‘version’ may continue so that the subject turns round several times on his own axis. Version is usually in the direction away from the discharging cerebral nerve cells—a left hemisphere focus causes turning to the right. Such seizures are therefore called adversive.

In the types of seizure described so far, there is an external manifestation-contraction of muscles driven by the discharging cerebral nerve cation-cells, so that this type of seizure is easily apparent to an observer.

Most people are right handed, the left hemisphere then being considered to be dominant. Language is very largely located in the dominant hemisphere. An aphasic partial seizure in which expression or comprehension of language is impaired may arise from a seizure discharge in the dominant temporal lobe.

Other groups of discharging cerebral nerve cells may not necessarily result in any external apparent event, only in a distorted internal perception. A focus in one parietal lobe (just behind the motor cortex) may only result in a transient disturbance of sensation, such as a perception of pins and needles in the opposite side of the face, arm, or leg. A seizure discharge in the anterior part of one temporal lobe may result only in the person perceiving a strange smell, unreal, often unpleasant, and yet often vaguely familiar. Similar hallucinations of distorted taste may also occur, which are usually perceived as unpleasant.

If the seizure discharge begins in a slightly different part of the temporal lobe, complex visual hallucinations may occur. A boy of 11 told one of us that he saw himself standing near a shower with another boy, whom he felt he knew yet could not name. This boy and he alternately put their feet under the running water, and this odd hallucination continued until the seizure ended.

Other seizures arising in the temporal lobe may cause a perception that events taking place have previously occurred in the person’s experience. This phenomenon is known as ‘deja vu’. Jamais vu is a phrase used to indicate that the person perceives familiar surroundings as unreal.

If such distorted perceptions occur they may disturb full consciousness—as defined by awareness of current events, interpretation of current events, and correct responsiveness to current events. All gradations of disturbance of consciousness may be seen. For example, the child or adult may respond appropriately to a question after a considerable delay, or he may respond inappropriately, or not at all. After the attack has terminated, people may say that they were dimly aware of ongoing real events, but this is not necessarily true, and the person may have no memory for all events during and for some time after the seizure. Partial seizures in which consciousness is disturbed are said to be complex partial seizures.

Sometimes seizures arising in the temporal lobe result in complex automatic behaviour — a so-called psychomotor seizure. The person may, for example, dress and undress repeatedly or drum his fingers on the table. Less complex, but more common manifestations, are repeated sucking or chewing or swallowing movements. The person will have no memory for these events after the attack.

Such automatic behaviour occurring during the seizure discharge must be distinguished from the common confusion following a grand mal attack, or following a prolonged temporal lobe seizure, for which the person will also be amnesic. This amnesia is, perhaps, analogous of the amnesia following a head injury, in which, for example, a young man will complete a game of rugby football after a collision resulting in a concussive head injury, yet afterwards he will be amnesic for this part of the game.

Emotional experiences are very frequent in partial seizures arising in the temporal lobe. These are often expressed just as ‘a horrible feeling’, but sometimes the sensation of fear is overpowering.

Sensations in the abdomen and chest often also occur. A common initial sensation is a vague feeling of discomfort in the upper abdomen, which rises rapidly into the chest and head. The abdominal sensation may be accompanied by contractions of the stomach and bowel resulting in audible rumbles.

Another frequent internal sensation is one of vertigo. People with seizures beginning in the temporal lobe may say that they are ‘dizzy.’ This word is used in different senses by various people, but some appear to perceive vertigo (a sense of dysequilibrium which may be rotational) as part of the seizure.

Any partial seizure may become secondarily generalized into a tonic-clonic seizure (grand mal seizure). Sometimes this happens so quickly that the partial (focal) onset is only apparent on careful analysis of an EEG recorded during a seizure.

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