sleep disorders

sleep disorders The ability to fall asleep, stay asleep, and wake up are all considered inalienable rights. We should neither stuporously wander about our houses nor suddenly decide to jump off our beds into imaginary swimming pools. The child's prayer, ‘Now I lay me down to sleep’, epitomizes the fond hope that sleep is a safe passage across a sea of unconsciousness undisturbed by life-threatening deficits in vital physiological processes. Still, it should have come as no surprise that a system as complicated and differentiated as the brain mechanisms underlying sleep and dreaming would have its own intrinsic propensity for dysfunction and disorder as well as its amazing capacity as a health-conveying operation. And the normal variation in sleep propensity, sleep depth, sleep length, and sleep stage distribution is already proof that such mundane events as excessive daytime sleepiness, or its converse, excessive night-time wakefulness (insomnia) should be viewed at least in part as expressions of extremes of normal physiology.

Yet even the most sophisticated and perspicacious sleep scientists were unprepared for the discovery that breathing sometimes stopped or was blocked in sleep (as it is in sleep apnea) or the recognition that all of the symptoms of the compelling need to sleep (as seen in narcolepsy) could be explained as abnormalities of sleep neurophysiology. More surprising still were the twin discoveries that sleepwalking, sleep-talking, and bedwetting had little to do with dreaming but that a previously unrecognized process, the REM sleep behaviour disorder, was not only dream enactment but the harbinger of degenerative disease of brain motor control systems!

There are three major kinds of sleep problems and each can be understood through sleep physiology:1. Difficulty falling asleep (which is caused by excessively strong or inadequately suppressed brain drives toward waking) — the classic example is insomnia.2. Difficulty staying awake (caused by excessively strong or inadequately suppressed brain drives toward sleep). The classic example is narcolepsy.3. Abnormal movements that occur as the depth of sleep varies over the course of the night. For example, the movement-generating centres of the brain can sometimes become active without the brain's consciousness-generating arousal systems becoming simultaneously activated to waking levels. The classic example is sleepwalking.The sleep apnea syndromes are an ambiguous but critically important class of sleep disorder with characteristics of all three categories. Victims of this life-threatening tendency to stop breathing when they fall asleep — and then to choke when they make compensatory efforts to wake up and breathe again — may be insomniac (because their bodies will literally not allow them to go to sleep); they may have excessive sleepiness by day (because they are chronically sleep deprived); and their laboured efforts to breathe while asleep can be seen as a form of chronic abnormal sleep movement, which, in the long term, may prove to be much more physiologically harmful than other sorts of abnormal sleep movements such as sleepwalking.

Sleep apnea sufferers are usually overweight (which makes breathing more difficult as the airway closes normally — causing snoring — at sleep onset) and male (which deprives them of the unexplained protection of sleep breathing afforded by female sex hormones). But they also just exaggerate the surprising normal tendency of men to have long pauses in their breathing efforts, especially during NREM sleep but also in REM. As their oxygen hunger increases and their brain alarm clock arouses them, they make a gasping effort to gulp air, at which point their flaccid, fat-compressed airway closes and they move even closer to self-strangulation. Because treatment is now quite effective it is crucial that any person suspected of having sleep apnea consult a physician or a sleep disorders centre.

Narcolepsy is a rare but instructive illness with four defining attributes: (i) excessive daytime sleepiness and irresistible attacks of sleep; (ii) the sudden loss of postural muscle tone (called cataplexy, often leading to total collapse; (iii) the occurrence of frightening dream hallucinations at sleep onset and upon awakening; and (iv) the persistence of REM sleep motor paralysis, also on arousal from sleep.

All of these symptoms are manifestations of a genetically-determined failure to inhibit REM sleep physiology, which most of us can do quite easily, especially during waking. Like new-borns, many adult narcoleptic patients have prolonged REM sleep bouts at sleep onset. Effective treatment is achieved using drugs that potentiate the brain chemicals responsible for effective waking, and/or suppression of the brain chemicals responsible for REM sleep.

Insomnia is by far the most prevalent disorder of sleep. It is also the most problematic to manage, because none of the myriad sedative drugs available for its relief is a physiological sleep inducer or enhancer. For this reason all of the effective sedatives have one or more defects: undesirable side-effects, diminished efficacy with prolonged use, or a worsening of symptoms upon withdrawal.

Because so much insomnia is psychologically and behaviourally driven, effective treatment should always include attention to such factors as (i) regular, early times of retirement; (ii) elimination of the commonly abused anti-sleep ingestants tobacco and alcohol; (iii) a review of daytime work and interpersonal concerns with special attention to identifying and eliminating the sources of nocturnal rumination and anxiety; (iv) the prescription of sleep-enhancing aerobic exercise; and (v) instruction in systematic body relaxation techniques.

This naturalistic approach to insomnia does not deny its sometimes strong physiological basis, which may demand pharmacological adjuncts, but it is cautious and conservative in warning against the undue expectation and the unacceptable risks of uncritical sedative treatment.

The REM sleep behaviour disorder is easily distinguished from ordinary sleepwalking. Sleepwalking is a self-limited and usually harmless problem of adolescence and early adulthood that occurs in NREM sleep and disappears when that sleep stage declines in the fourth decade. By contrast, the REM sleep behaviour disorder usually begins at that age or later, and reflects the dangerous and prognostically grave failure to inhibit the motor commands of REM sleep that are normally experienced as only the illusion of movement during dreaming.

Early degeneration of the brain (and especially Parkinson's disease) is heralded by REM sleep behaviour disorder, but it has also recently been reported to arise in younger subjects who have been treated for depression with drugs that specifically potentiate serotonin, one of the chemicals that the brain uses to energize itself in waking and to influence the excitability of the motor system in all of its states.

The study of sleep disorders is still a young, rapidly-developing field at the interface of neurology, psychiatry, and internal medicine. Its inventory of disorders, its methods of investigation, and its approaches to treatment can all be expected to change rapidly in the next few decades.

J. Allan Hobson

See also body clock; sleep; snoring.