What is the role of ictal EEG in the workup of Lennox-Gastaut syndrome (LGS)?

Updated: Nov 09, 2018
  • Author: Koshi A Cherian, MD; Chief Editor: Amy Kao, MD  more...
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Answer

During a tonic seizure, the EEG is characterized by a diffuse, rapid (10-13 Hz), low-amplitude activity pattern, mainly in the anterior and vertex areas ("recruiting rhythm") that progressively decreases in frequency and increases in amplitude.

A brief generalized discharge of slow spike waves or flattening of the recording may precede this pattern. Diffuse slow waves and slow spike waves may follow it.

These fast discharges are common during non-REM sleep. Unlike tonic-clonic seizures, no postictal flattening occurs with these seizures. Clinical manifestations appear 0.5-1 second after the onset of EEG manifestations and last several seconds longer than the discharge.

During an atypical absence seizure, the EEG is characterized by diffuse, slow (2-2.5 Hz), and irregular spike waves, which may be difficult to differentiate from interictal bursts. Occasionally, discharges of rapid rhythms may be observed preceded by flattening of the record for 1-2 seconds, followed by progressive development of irregular fast rhythm in the anterior and central regions, and ending with brief spike waves.

During atonic, massive myoclonic, and myoclonic-atonic seizures, the EEG is characterized by slow spike waves, polyspike waves, or rapid diffuse rhythms. Simultaneous video/EEG recording can help differentiate these seizure types. In most patients, these 3 types of seizures coexist.

The EEG during absence status epilepticus reveals continuous spike wave discharges, usually at a lower frequency than at baseline, and rapid rhythms during tonic status epilepticus.


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