Sleep Disorders

Sleep disorders are an important part of neurology examinations as they require a strong knowledge of complex diagnostic studies such as EEG, and also of a multitude of medications. In this chapter, you will learn sleep waveforms using real EEG tracings, and review high-yield treatments for sleep disorders. Test your knowledge at the end with practice questions and flashcards!

Authors: Jody Manners MD, Brian Hanrahan MD

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Circadian Rhythms

Defined as physical, mental, and behavioral changes following roughly a 24-hour cycle, responding primarily to light and darkness in the environment.
- They are endogenous and self-sustained but can be modulated by external cues (zeitgebers).

Table of endogenous and self-sustained zeitgebers

- - Ultradian Rhythms occur more frequently than once every 24 hours, such as the stages of sleep, patterns of hormonal release, and appetite regulation.
  - Infradian Rhythms are less frequent than 24 hours, often weekly, monthly, or seasonally. Infradian rhythms can be associated with conditions like seasonal affective disorder (SAD) or hormone-related mood disorders.
The suprachiasmatic nucleus (SCN) of the hypothalamus, the central clock is responsible for synchronizing 24-hour circadian rhythms.
- - The axons of light-sensitive neurons in the retina provide information to the SCN, allowing the internal clock to be synchronized with the outside world.
  - Melatonin, secreted by the pineal gland, has a key role in sleep onset. Its secretion is inhibited by light and permitted by darkness, signaling the body when it’s night-time.

Remember Melatonin release is stimulated by darkness and inhibited by light

Physiological processes influenced by circadian rhythms
- - Hormone Release
    - - Cortisol: Follows a diurnal pattern, peaking in the early morning to help promote alertness and metabolic functions and gradually declining throughout the day.
      - Growth Hormone (GH): Significant releases of GH, happen in the early phases of sleep.
  - Body Temperature: Core body temperature dropping during the night and rises during the day (see graph below)

Phases of Sleep

Wakefulness

Characterized by alpha frequency activities, sporadic eye movements, and a posteriorly dominant alpha rhythm that attenuates with eye-opening.

NREM sleep

Stage N1 (5% of total sleep): Associated with an emergence of theta activity, and slow roving eye movements.
- Young adults spend the least amount of time in NREM stage 1 sleep.
Stage N2 (45-55% of total sleep):
- The stage at which adults spend the most time during normal sleep.
- Characterized by the presence of either sleep spindlesand/or K-complexes with theta range background activity.
- Sleep spindles are thought to be generated by the reticular thalamic nucleus.
- Stage N3 (15-20% of total sleep):
  - k.a “deep sleep” or “slow-wave sleep” (no longer called “stage 4 sleep”)
  - EEG will show slow-waves and high amplitude delta waves.
  - Parasomnias tend to occur during this stage.

REM sleep

20-25% of sleep.
Normally occurs ~90 minutes into sleep.
Characterized by a desynchronized low voltage, high-frequency background.
There will be decreased EMG activity (REM atonia).
Sharply peaked irregular eye movements with lateral rectus spikes (see below) can be seen ON eeg. Note the lack of muscle artifact.