What are the EEG changes characteristic of Lennox-Gastaut syndrome (LGS)?

Updated: Oct 01, 2020
  • Author: Raj D Sheth, MD; Chief Editor: Selim R Benbadis, MD  more...
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The EEG in affected patients shows an abnormally slow background and diffuse slow spike and slow wave (< 2.5 Hz) activity (see the images below). The slow spike and wave activity serves to differentiate (poor prognosis) Lennox-Gastaut syndrome from benign absence epilepsy, in which diffuse 3-Hz spike and wave activity is seen, and from some of the more benign myoclonic types of epilepsy characterized by fast spike and wave (> 2.5 Hz) activity, which carries a dramatically better prognosis than Lennox-Gastaut syndrome. Many other epilepsy syndromes overlap with Lennox-Gastaut syndrome, however, including myoclonic astatic epilepsy of Doose and other severe myoclonic epilepsies.

Slow (&lt; 2.5 Hz) electroencephalographic spike a Slow (&lt; 2.5 Hz) electroencephalographic spike and wave discharges associated with atypical absence seizures (ie, Lennox-Gastaut syndrome).
Slow (&lt; 2.5 Hz) electroencephalographic spike a Slow (&lt; 2.5 Hz) electroencephalographic spike and wave discharges in atypical absence epilepsy (ie, Lennox-Gastaut syndrome).

EEG features of Lennox-Gastaut syndrome may be divided into interictal and ictal.

Characteristic interictal EEG features consist of background slowing and diffuse slow spike and wave activity that last from several minutes to a near continuous state. The duration of the epileptiform discharges tends to correlate with epilepsy control, with shorter durations occurring in patients with better control of seizures. Spikes, or more commonly sharp waves, are typically 200 milliseconds in duration and are followed by slow waves. Polyspike discharges are seen in those epilepsy variants with prominent myoclonic seizures or during non–rapid eye movement (REM) sleep.

Ictal EEG features have varying electrographic accompaniment with the seizure type. 

Generalized paroxysmal fast activity (GPFA) is typically fast activity (> 10 Hz) and may be subclinical versus clinical (such as tonic versus atonic seizures). [3]  Typically GPFA can be seen in LGS (see image below).  

Electroencephalogram demonstrating paroxysmal fast Electroencephalogram demonstrating paroxysmal fast activity as can be seen in Lennox-Gastaut syndrome.

For more information, see Lennox-Gastaut Syndrome.

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