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.
Long-term therapy may include the use of antiepileptic drugs, surgical therapy, diet therapy (ketogenic diet), vagus nerve stimulation, or deep brain stimulation. Terminology
Generalized tonic–clonic seizures can have a focal onset (described above) that progresses into a generalized seizure or be a generalized seizure at the onset. The term "Grand Mal" is outdated and nonspecific, referring to generalized tonic-clonic seizures with either a focal or generalized onset. See also
Focal seizure
Absence seizure
Epileptic seizure
Non-epileptic seizure
Tonic (physiology)
Clonus
Postictal state
Electroencephalography

References
External links

Generalized tonic–clonic seizure at Curlie