NEUROLOGIC SLEEP DISORDERS  

Christopher R. Jones, M.D.

 

 

OBJECTIVES:

1.Understand the difference between sleep and coma.

2. Be able to list all of the following as being factors that effect the level of sleepiness or alertness:

i. circadian time

ii. duration of prior wakefulness

iii. average total sleep time per 24 hour day

iv. average sleep quality during the major sleep episode

v. presence of stimulant or sedative drugs

vi. presence of an intrinsic disorder of alertness

3. Be able to describe the type of information provided by polysomnography.

4. Be able to by describe the type of information provided by the Multiple Sleep Latency Test.

5. Know the cardinal clinical and polygraphic features of narcolepsy.

6. Know the cardinal clinical and polysomnographic features of restless legs syndrome.

 

Main Points

1. Sleep is an active brain process and therefore requires a healthy nervous system.

2. Sleep disorders are common.

3. Sleep disorders can cause significant morbidity and mortality.

4. Restless legs syndrome is a common cause of difficulty initiating and maintaining sleep at night.

5. Narcolepsy is a relatively uncommon cause of excessive sleepiness during the day.

 

I. INTRODUCTION

Sleep disorders are common in all age groups.

Difficulty initiating and /or maintaining sleep: Prevalence > ~5%. Usually depressive " anxious features.

            Also: poor sleep habits, shift work schedule, drug effect, breathing & movement disorders, pain.

Excessive daytime sleepiness

Self-imposed inadequate sleep time, obstructive sleep apnea,  narcolepsy.

Significant morbidity and mortality: Most sleep disorders are chronic & life-long.

Sleep apnea may increase mortality

Night terrors, REM Behavior Disorder & narcolepsy Y injuries.

Sleepiness causes decreased driving safety, quality of life, social functioning & job performance.

 

II. NORMAL SLEEP

Polysomnographic determination of sleep-wake stage:

Brain wave (EEG), eye movement (EOG), & skeletal muscle tone (EMG) measurements required.

 

DEFINITION OF SLEEP/WAKE STAGES AS MEASURED BY POLYSOMNOGRAPHY      BRAIN STATE BRAIN WAVE EYE MOVEMENT MUSCLE TONE PHYSIOLOGY & PATHOLOGY     Wake Prominent posterior alpha (8-12 Hz) rapid high Rapid CNS responses, regular breathing     1   Alpha disappears; theta slowing (4-7 Hz) slow, rolling moderate Slow CNS responses, periodic breathing, sleep apnea     2 K-complexes, 12-14 Hz Sleep spindles none low Subjective sleep onset, decreased seizure threshold, sleep apnea     3 20% of EEG is delta activity none low High arousal threshold, night terrors and sleep walking, regular breathing     4 50% of EEG is delta activity rapid very low Rhythm but, hypo-ventilation dreams, muscle paralysis, low ventilatory drive, sleep apnea     REM Low voltage, mixed frequency

            

 

  

  Measurement of sleep stages and associated neuro-cardio-pulmonary physiology = Polysomnography

                        Sleep staging (EEG, EOG, neck EMG) as above

Muscle tone in the neck and extremities (surface electromyogram - EMG)

Heart rhythm (electrocardiogram - EKG)

Breathing movements of the chest wall and abdomen (movement detectors)

Airflow at the nose and mouth (temperature and CO2 detectors)

Airway noise at the neck (snore microphone)

Arterial oxygen saturation (pulse oximeter)

Main purpose: provide information on the quantity and quality of sleep.  

Physiology and pathology associated with Sleep Stages:

Light NREM sleep (stage 1 = drowsiness, stage 2 = unconscious):

            Low arousal threshold.

            Respiratory control instability promotes breath holding alternating with over-breathing

            Decreased upper airway dilator tone promotes throat collapse

Impaired Driving safety, job performance and social functioning during drowsiness.

Information presented during stage 1 sleep is poorly remembered.

Normal, startle reactions (hypnic jerks).

Some movement disorders (e.g. Restless Legs Syndrome) are facilitated.

Primary generalized seizures and focal seizures are facilitated.

Deep NREM sleep (stages 3 & 4)

High arousal threshold.

Mental slowness & incoordination upon arousal.

More regular breathing rhythm.

Lower brain metabolic rate than the other stages of sleep or wakefulness. 

Sleep walking.

REM sleep

Generalized muscle paralysis:

                                    Limbs, chest wall, upper airway dilator muscles.

Respiratory decompensation with restrictive or obstructive pulmonary disease.

Spares the thoraco-abdominal diaphragm and extraocular muscles.

Periodic Leg Movements of Sleep unlikely.

Normal (physiologic) hallucinations, nightmares.

Increased brain metabolism (similar to that of wakefulness).

REM Behavior Disorder (acting out the dream while still asleep).

 

SLEEP PATTERN OF A NORMAL YOUNG ADULT AS MEASURED BY POLYSOMNOGRAPHY

   

High Quality Chart Coming Soon!

 

  

Regulation of Total Sleep Time:

Sleep deprivation Y compensatory increase in SWS and REM sleep for one to three nights.

 

Circadian Rhythm of Sleepiness:

The ability to fall asleep varies in a predictable way across the 24 hour day.

Sleepiness gradually decreases during the morning hours from 6:00 A.M. until noon.

Sleepiness increases in the early afternoon.

Sleepiness then decreases to its daily nadir around 7:00 to 9:00 P.M

Highest level of sleepiness at about 4:00 A.M.

"Biological clock" in the suprachiasmatic nucleus of the anterior hypothalamus.

 

III. Distinction Between Sleep and Coma

Sleep is normal unconsciousness; coma is abnormal unconsciousness.

Sleep serves a useful and restorative purpose for the brain; coma generally does not.

Sleep is regulated by the brain; coma is imposed on the brain by some sort of external insult or influence. Sleep is modulated by the circadian biological clock; coma is not modulated by the clock.

Sleep is heterogeneous (consists of different sleep stages); coma is more homogeneous.

Sleep can be reversed by external stimuli; coma cannot be reversed by stimulation.

Most stages of sleep (especially REM sleep) probably have a higher brain metabolic rate than coma.

Normal sleep brain waves are usually different from the EEG patterns of coma.  

IV. Determinants Of Alertness (Neurologic Arousal):

Circadian Time

Duration of Prior Wakefulness

Average Total Sleep Time Per Day

Average Sleep Quality

Drug Effects

Presence of An Intrinsic Disorder of Alertness

Narcolepsy

   

SELECTED NEUROLOGIC SLEEP DISORDERS

 

1.  Narcolepsy

Prevalence: ~1 in 2,000, but under-diagnosed.

Main symptom: disabling sleepiness

            Especially in sedentary, monotonous, non-threatening conditions.

            Similar to the sleepiness experienced by anybody after prolonged sleep deprivation.

            Driving safety is impaired, school work is very difficult and job performance suffers.

            Total sleep time over the entire 24 hour day is close to the normal range.

            Inability to sustain wakefulness causes frequent, short naps

Neurophysiology: abnormalities in the control of REM sleep

            No increase in total daily amount of REM sleep, but

            Fragments of REM sleep occur at inappropriate times:

                        Daytime sleepiness may represent an abnormal pressure to enter REM sleep.

            Hypnogogic hallucinations may be dreaming imagery which has "escaped" REM sleep.

            Sleep paralysis and cataplexy may represent episodes of REM-related muscle atonia.

The full tetrad of daytime sleepiness, cataplexy, hypnogogic hallucinations and sleep paralysis is only seen in about 10 to 20% of narcoleptics.

Pathognomonic auxiliary symptom: cataplexy

Sudden, brief loss of muscle tone in leg, axial, eyelid or other bilateral muscle groups usually precipitated by a sudden laughter, anger or other emotion. Consciousness is preserved.

Differential diagnosis of cataplexy: epileptic and ischemic "drop attacks", the sudden falling of hysterical conversion reaction or malingering, periodic paralysis, myasthenia gravis. 

 

Pathophysiology: loss of excitatory hypothalamic neurotransmitter (hypocretin), ? why

Genetics: HLA genetic marker QB1*0602

Familial tendency, but mode of inheritance not known (probably polygenic).

Monozygotic twins are only about 30% concordant (environmental influences)

Natural history:

            Onset usually by age 15-25 years.

Usually not progressive after the first few years of symptoms.

Laboratory tests:

Polysomnography: identify treatable causes of sleep fragmentation, such as sleep apnea.

Multiple sleep latency test (MSLT): Five nap opportunities spread out across the day.

            Narcoleptic MSLT: rapid sleep onset and short latency to REM sleep.

Assumptions:    1) Sleepy people fall asleep more quickly than normal alert people.

                        1) Sleepiness can be quantified using the MSLT.

                        2) Narcoleptic sleepiness is associated with short REM latency.

False positive MSLT: sleep apnea, voluntary sleep deprivation, shift work schedule, "jet lag, recent abrupt cessation of stimulant drugs.