What are focal EEG asymmetries of sleep architecture?

Updated: Oct 09, 2019
  • Author: Alexis D Boro, MD; Chief Editor: Selim R Benbadis, MD  more...
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Prolonged and asynchronous sleep spindles are a normal finding before the age of 2 years. In older individuals, prolonged and large amplitude sleep spindles are usually caused by medications, frequently benzodiazepines. Asynchronous sleep spindles beyond the age of 2 years are abnormal. Bilaterally prolonged spindles have been associated with mental retardation. The unilateral absence, decreased amplitude, or frequency of sleep spindles at any age is abnormal and is associated with ipsilateral lesions. The lesion may be anywhere along the thalamocortical axis. Asymmetric vertex waves similarly suggest a lesion on the side of the depressed amplitude. See the image below.

Asymmetric sleep spindles. This EEG is from a 12-y Asymmetric sleep spindles. This EEG is from a 12-year-old boy with seizures. The frontally displaced 12-Hz sleep spindles are attenuated on the right. Frontally displaced spindles are a normal variant. They are often slightly slower than, and coexist with, centrally predominant spindles. However, the asymmetry of the spindles is an abnormality and could be a consequence of a structural lesion on the right.

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