|Classification and external resources|
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 are induced deliberately in electroconvulsive therapy.
The vast majority of generalized seizures are idiopathic. 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. 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.
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. The lesions (i.e., scar tissue) caused by the loss of these neurons can result in groups of neurons episodically firing abnormally, creating a seizure.
- The person may feel a sense of strong déjà vu, lightheadedness and/or dizziness, unusual (and possibly inappropriate) emotions, intense feelings of mental discomfort, foreboding, or personal doom, altered vision and hearing (which may or may not include hallucinations), and sometimes other symptoms. This is actually a simple partial seizure. Sometimes, the person will lose complete awareness and start making odd or pointless repetitive movements (such as picking at clothes or lip smacking) towards the end of the aura, at which point the seizure has progressed to become a complex partial seizure.
- The aura stage occurs because tonic–clonic seizures often start in an isolated area of the brain, known as the seizure focus, and gradually spread to the whole brain, whereupon loss of consciousness occurs and becomes a tonic–clonic seizure. An aura may last as little as a few minutes or as long as several hours, though some with epilepsy do not experience them at all. Many auras are followed by a tonic–clonic seizure.
- Tonic phase
- The person will quickly lose 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 person to fall if standing or sitting. The tonic phase is usually the shortest part of the seizure, usually lasting only a few seconds. The person may also express brief vocalizations like a loud moan or scream during the tonic stage, due to air forcefully expelled from the lungs.
- Clonic phase
- The person'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 person may roll and stretch as the seizure spreads. The eyes typically roll back or close and the tongue often suffers bruising or lacerations sustained by strong jaw contractions. The lips or extremities may turn slightly bluish (cyanosis) and incontinence is seen in some cases.
Due to physical and nervous exhaustion, postictal sleep with stertorous breathing invariably follows a tonic–clonic seizure. Confusion and complete amnesia upon regaining consciousness is usually experienced and slowly wears off as the person becomes gradually aware that a seizure occurred.
- David Y Ko (5 April 2007). "Tonic–Clonic Seizures". eMedicine. Retrieved 2008-03-19.
- "Epilepsy Action: Simple Partial Seizures". Epilepsy Action. British Epilepsy Association. 19 February 2008. Retrieved 2008-03-19.
- "Seizure Mechanisms and Threshold". Epilepsy Foundation. Retrieved 2008-03-19.
- Ruben Kuzniecky, M.D. (16 April 2004). "Looking at the Brain". epilepsy.com. Epilepsy Therapy Project. Retrieved 2008-03-19.