This is the classic form of epileptic attack, the 'convulsion' or 'fit' that typifies epilepsy in the public imagination. It has a number of well-defined stages. It is sometimes preceded by a prodromal period during which an attack is anticipated, often by an ill-defined vague feeling or sometimes more specifically, for instance, by the occurrence of increasing myoclonic jerking. If an aura then occurs (in fact a simple or complex partial seizure) in the seconds before the full-blown attack, this indicates that the tonic-clonic seizure is secondarily generalized. The seizure is initiated by loss of consciousness, and sometimes the epileptic cry. The patient will fall if standing, there is a brief period of tonic flexion, and then a longer phase of rigidity and axial extension, with the eyes rolled up, the jaw clamped shut, the limbs stiff, adducted and extended, and the fists either clenched or held in the main d'accoucheur position. Respiration ceases and cyanosis is common. This tonic stage lasts on average 10-30 seconds and is followed by the clonic phase, during which convulsive movements usually of all four limbs, jaw and facial muscles occur; breathing can be stertorous; and saliva (sometimes blood-stained owing to tongue biting) may froth from the mouth. The convulsive movements decrease in frequency (eventually to about four clonic jerks per second), and increase in amplitude as the attack progresses.
Autonomic features such as flushing, changes in blood pressure, changes in pulse rate and increased salivation are common. The clonic phase lasts between 30 and 60 seconds and is followed by a further brief tonic contraction of all muscles, sometimes with incontinence. The final phase lasts between 2 and 30 minutes and is characterized by flaccidity of the muscles. Consciousness is slowly regained.
The plantar responses are usually extensor at this time and the tendon jerks are diminished. Confusion is invariable in the postictal phase. The patient often has a severe headache, feels dazed and extremely unwell, and often lapses into deep sleep. On awakening minutes or hours later, there may be no residual symptoms or, more commonly, persisting headache, dysthymia, lethargy, muscle aching and soreness (including stiffness of the jaw).
Tonic-clonic seizures can occur at any age and are encountered in many different types of epilepsy, including idiopathic generalized epilepsy, symptomatic generalized epilepsies, epileptic encephalopathies, in various epilepsy syndromes, in febrile convulsions, and in acute symptomatic seizures. They have no pathological specificity.
The interictal EEG has a variable appearance, depending on the cause of the tonic-clonic seizures. During the tonic phase, the ictal EEG may show generalized flattening (desynchronization). This is followed by low-voltage fast activity and then 10 Hz rhythms appear and increase in amplitude (recruiting rhythms). These are followed some seconds later by slow waves increasing in amplitude and decreasing in frequency from 3 to 1 Hz. During the clonic phase, the slow waves are interrupted by bursts of faster activity (at about 10 Hz) corresponding to the clonic jerks, and as the phase progresses, the slow waves widen and these bursts become less frequent. With scalp recordings, however, these EEG patterns will often be obscured by artefact from muscle and movement. As the jerks cease, the EEG becomes silent and then slow delta activity develops. This persists for a variable period and the EEG background rhythms then slowly increase in frequency. Minutes or hours usually elapse before the EEG activity returns to normal. In patients with idiopathic generalized epilepsy, the EEG in the pre-ictal period may show increasing abnormalities with spike-wave or spike paroxysms.
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