Generalised tonic-clonic seizure

Tonic–clonic seizures (formerly known as grand mal seizures) are a type of generalized seizure that affects the entire brain. Tonic–clonic seizures are the seizure type most commonly associated with epilepsy and seizures in general, though it is a misconception that they are the only type.

Tonic–clonic seizures can be induced deliberately in electroconvulsive therapy.

Pathophysiology

The vast majority of generalized seizures are idiopathic.^[1] However, some generalized seizures start as a smaller seizure such as a simple partial seizure or a complex partial seizure and then spread to both hemispheres of the brain. This is called a secondary generalization.^[2] Factors could include chemical and neurotransmitter imbalances and a genetically determined seizure threshold, both of which have been implicated. The seizure threshold can be altered by fatigue, malnutrition, lack of sleep or rest, hypertension, stress, diabetes, the presence of neon or xenon strobe-flashes, fluorescent lighting, rapid motion or flight, blood sugar imbalances, anxiety, antihistamines and other factors.^[3]

In the case of symptomatic epilepsy, it is often determined by MRI or other neuroimaging techniques that there is some degree of damage to a large number of neurons.^[4] The lesions (i.e., scar tissue) caused by the loss of these neurons can result in groups of neurons forming a seizire 'focus' area, episodically firing abnormally, creating a seizure if the focus is not abolished or suppressed via anti-convulsant drugs.

Phases

A tonic–clonic seizure comprises two phases, the tonic phase and the clonic phase.

Tonic phase

The patient will quickly lose consciousness (though not all generalized tonic-clonic seizures involve a full loss of consciousness), and the skeletal muscles will suddenly tense, often causing the extremities to be pulled towards the body or rigidly pushed away from it, which will cause the patient to fall if standing or sitting. The tonic phase is usually the shortest part of the seizure, usually lasting only a few seconds. The patient may also express brief vocalizations like a loud moan upon entering the beginning seizure with the tonic stage, due to air forcefully expelled from the lungs.

Clonic phase

The patient's muscles will start to contract and relax rapidly, causing convulsions. These may range from exaggerated twitches of the limbs to violent shaking or vibrating of the stiffened extremities. The patient may roll and stretch as the seizure spreads. The eyes typically roll back or close and the tongue often suffers bruising or crushing injuries sustained by strong jaw contractions if the patient does not prepare for the seizure by biting down on -for example- a leather belt or cloth. The lips or extremities may turn slightly bluish (cyanosis) and incontinence is seen in some cases.

Due to physical, mental and nervous exhaustion, postictal sleep with stertorous breathing invariably follows a tonic–clonic seizure. Confusion and total amnesia upon regaining consciousness is usually experienced and slowly wears off as the patient becomes gradually aware that a seizure occurred and remembers who and what he is and where he is. Occasionally the patient may vomit or burst into tears from the experienced mental trauma. An additional smaller seizure can occur several minutes after the main seizure, particularly if the patient's seizure threshold has been brought unusually low by known factors or combinations of such - for example severe hangovers, sleep deprivation, prolonged physical tiredness or caffeine.

See also

• Absence seizure
• Epileptic seizure
• Non-epileptic seizure

References

External links

• Generalised tonic-clonic seizure at DMOZ