Which findings on EEG are characteristic of Lennox-Gastaut syndrome (LGS)?

Updated: Nov 09, 2018
  • Author: Koshi A Cherian, MD; Chief Editor: Amy Kao, MD  more...
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No laboratory investigations are known to aid in the diagnosis of LGS.

EEG (waking and sleep) is an essential part of the workup. Interictal EEG may demonstrate the following characteristics:

  • A slow background that can be constant or transient

  • Awake – Diffuse slow spike wave

  • Non-REM sleep – Discharges that are more generalized and more frequent, consisting of polyspikes and slow waves

  • REM sleep – Decreased spike waves

Ictal EEG may demonstrate the following characteristics:

  • Tonic seizure – Diffuse, rapid, low-amplitude activity pattern that progressively decreases in frequency and increases in amplitude; may be preceded by a brief generalized discharge of slow spike waves or flattening of the recording or followed by diffuse slow waves and slow spike waves; no postictal flattening

  • Atypical absence seizure – Diffuse, slow, and irregular spike waves; occasionally, discharges of rapid rhythms preceded by flattening of the record for 1-2 seconds, followed by progressive development of irregular fast rhythm in anterior and central regions and ending with brief spike waves

  • Atonic, massive myoclonic, or myoclonic-atonic seizure – Slow spike waves, polyspike waves, or rapid diffuse rhythms

  • Absence status epilepticus – Continuous spike wave discharges, usually at a lower frequency than at baseline, and rapid rhythms during tonic status epilepticus

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