Generalized Tonic-Clonic Seizures

The EEG in focal seizures is characterized by focal spikes or sharp waves. There is often a relationship between the location of the spikes and the seizure type, that is, occipital lobe spikes are associated with occipital lobe seizures, while frontal lobe spikes are associated with frontal lobe seizures.

Different types of seizures may evolve in temporal succession in the same patient. For example, a focal seizure starting with normal consciousness and awareness may become associated with alteration in consciousness and subsequently evolve to a generalized convulsive seizure as the seizure starts within a local neural circuit and then spreads to involve an increasing proportion of the brain and ultimately both hemispheres.

GENERALIZED SEIZURES: TONIC-CLONIC SEIZURE

A generalized tonic-clonic, or grand mal seizure, is the most severe type of seizure. It starts with a sudden loss of consciousness and generalized tonic stiffening and extension of the body secondary to a widespread contraction of the muscles. The patient may utter a piercing cry resulting from forced expiration of air from the lungs through closed vocal cords. Cessation of respirations with associated cyanosis is secondary to the tonic muscle contractions that prevent normal respiratory movements. The patient often bites his tongue during this phase of the seizure. Salivation occurs because the patient cannot swallow during the seizure. In addition, urinary incontinence is often present.

The initial tonic phase of the seizure is followed by the clonic phase, in which generalized bilaterally synchronous clonic jerks of the body alternate with brief periods of relaxation. As the periods of relaxation become more prolonged, the clonic movements gradually decrease and finally cease.

During the postictal period after the seizure, the patient is limp, obtunded, and unresponsive. The actual seizure may last about 1 to 2 minutes, while the postictal phase may last from 5 to 20 minutes. Afterward, the patient may arouse, but remains confused, and if left undisturbed, may sleep for an hour or so and awaken with a headache and generalized muscle soreness.

Generalized tonic-clonic seizures may occur at any age. They may be primary generalized seizures, which are generalized from onset, or secondary generalized seizures, which start as focal seizures and then become generalized as the seizure activity progresses to involve widespread areas of the brain.

The EEG of a GTC seizure shows various types of seizure activity that correspond to the different phases of the seizure. During the tonic phase, the EEG shows fast, repetitive, generalized spike discharges. During the clonic phase, the EEG shows spike-and-wave discharges, with the spike corresponding to the clonic jerks and the slow wave to the period of relaxation. Finally, during the postictal phase, the EEG shows generalized attenuation of background activity followed by slowing, which gradually decreases as the patient recovers from the seizure.

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