Slow Spike and Wave (SSW) Complexes

Posted on

December 29, 2023

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Yamada, Thoru, and Elizabeth Meng. Practical Guide for Clinical Neurophysiologic Testing: EEG. Available from: Wolters Kluwer, (2nd Edition). Wolters Kluwer Health, 2017.  Greenfield, John, L. et al. Reading EEGs: A Practical Approach. Available from: Wolters Kluwer, (2nd Edition). Wolters Kluwer Health, 2020.

The SSW complexes consist of biphasic or triphasic sharp or spike waves followed by high- voltage (300μV to 400μV+) slow waves. The frequency of SSW complexes falls between 1.5Hz and 2.5Hz. This is slower and more irregular than the atypical absence 3Hz spike-wave complexes associated with absence epilepsy. The bursts are usually bilaterally synchronous but may be asymmetrical. The sharp and slow-wave complex is followed by a slower waveform in the delta frequency range.

Question:

The interictal EEG of a patient with Lennox Gastuat Syndrome (LGS), may feature focal or multifocal spike-and-waves or sharp-slow waves, with anterior predominance. Slow (<2.5 Hz) spike-and-waves (SSW) and paroxysmal fast activity (10 Hz+) are mandatory requirements interictally for a LGS diagnosis. What state of consciousness are these waveforms found?

Awake

Drowsy

Slow Wave Sleep

REM

Correct Answer:

Interictal EEG of LGS: Slow (<2.5 Hz) spike-and-wave and paroxysmal fast activity (10 Hz or greater) in slow sleep are mandatory requirements. Periods of suppression of the EEG may also occur.

LGS, first described in the work of Lennox in1945 and elaborated by Gastaut in 1966. Classically, LGS begins between 2- 5 years of age and falls in the category of generalized

symptomatic epilepsies.

Defining characteristics:

(1) Multiple seizure types, high seizure frequency, including myoclonic, atypical absence, tonic, and atonic seizures, and partial seizures and GTC’s may occur. Status epilepticus is seen in most patients at some point.

(2) Mental retardation and/or behavioral disorders are always present.

(3) EEG findings of diffuse slowing with slow spike-and-wave discharges (<3 Hz) that increase during sleep; multifocal independent spikes and generalized paroxysmal fast activity (GPFA) are also often recorded.

Ictal EEG: refer to individual seizure type.

The prognosis for complete seizure control is poor, and cognitive deterioration can occur. Many patients with the diagnosis of LGS evolve from West syndrome or other generalized epilepsies, this evolution taking an average of 1.9 years.

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