A generalized tonic–clonic seizure, or GTCS, previously known as a Grand mal seizure, is a type of generalized seizure that produces bilateral, convulsive tonic and then clonic muscle contractions. Tonic-clonic seizures are the seizure type most commonly associated with epilepsy and seizures in general and the most common seizure associated with metabolic imbalances. It is a misconception that they are the sole type of seizure, as they are the main seizure type in approximately 10% of those with epilepsy.These seizures typically initiate abruptly with either a focal or generalized onset, the former being known as focal to bilateral tonic-clonic seizure. The seizure itself includes tonic (sustained) and then clonic (repetitive short) contractions. In some seizures, the tonic phase may be preceded by brief, arrhythmic muscle jerks (myoclonus), by a clonic phase or by an absence seizure. After the GTCS, there is an extended postictal state where the person is unresponsive and commonly sleeping with loud snoring. There is usually pronounced confusion upon awakening. Causes
The vast majority of generalized tonic-clonic seizures have a focal origin they start as a smaller seizure that occurs solely on one side of the brain and is referred to as a focal (or partial) seizure. These unilateral seizure types (formerly known as simple partial seizure or a complex partial seizure and now referred to as focal aware seizure and focal impaired awareness seizure, respectively) can then spread to both hemispheres of the brain and cause a generalized tonic-clonic seizure.
This type of seizure has a specific term called "focal to a bilateral tonic-clonic seizure. Other generalized tonic-clonic seizures are idiopathic, start in large networks involving both hemispheres, and have a presumed genetic cause. Precipitating factors include chemical and neurotransmitter imbalances and a genetically or situationally 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 strobe-flashes or simple light/dark patterns, raised estrogen levels at ovulation, fluorescent lighting, rapid motion or flight, blood sugar imbalances, anxiety, antihistamines and other factors. Tonic–clonic seizures can also be induced deliberately with electroconvulsive therapy.In the case of symptomatic focal epilepsy, the cause is often determined by MRI or other neuroimaging techniques showing 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 forming a seizure "focus" area with episodic abnormal firing that can cause seizures if the focus is not abolished or suppressed via anticonvulsant drugs. Mechanism
Prodrome
Most generalized tonic–clonic seizures begin without warning and abruptly, but some epileptic patients describe a prodrome. The prodrome of a generalized tonic–clonic seizure is a sort of premonitory feeling hours before a seizure. This type of prodrome is distinct from stereotypic aura of focal seizures that become generalized seizures. Phases
A tonic–clonic seizure comprises three phases: the tonic phase, clonic phase and postictal phase. Tonic phaseThe tonic phase is usually the first phase.