Tonic seizures are brief seizures (usually <60 seconds) consisting of the sudden onset of increased tone in the extensor muscles.7-9 If standing, the patient typically falls to the ground. These seizures are invariably longer than myoclonic seizures. Occasionally tonic seizures terminate with a clonic phase.
The degree to which consciousness is impaired is often difficult to assess. In seizures lasting longer than a few seconds, impairment of consciousness is usually apparent.
Postictal impairment with confusion, tiredness, and headache is common. The degree of postictal impairment is usually related to the duration of the seizure.
Electromyographic activity is dramatically increased in tonic seizures.
Tonic seizures are frequently seen in patients with the Lennox-Gastaut syndrome, a disorder consisting of mixed seizure types, mental retardation, and the EEG findings of a slow spike-and-wave pattern.10-12 Seizures are usually more frequent at night.
Tonic seizures have been divided into four types:
In a study of epileptic falls in children, Ikeno et al13 described two types of tonic seizures:
Egli et al7 described tonic seizures that lead to falls as “axial spasms.” Reflecting a uniform pattern of movement, these seizures consist of moderate flexion of the hips, upper trunk, and head lasting from 0.5 to 0.8 second. The arms are almost always abducted, elevated, and in a semiflexed position. The fall is provoked by the rapidity and violence of the flexion in the hips.
Ictal manifestations of tonic seizures usually consist of bilateral synchronous spikes of 10 to 25 Hz, of medium to high voltage, with a frontal accentuation. Simple flattening or desynchronization also may occur. Occasional multiple spike-and-wave or diffuse slow activity may occur during a tonic seizure (See EEG).
Multiple spike-and-wave activity in a patient with tonic seizures.
Reviewed and revised January 2004 by Gregory L. Holmes, MD, Dartmouth Medical School
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