Causes of Sleep Disorders
What are the causes of some of the most common sleep disorders? Although the answer is often unknown, we are slowly learning what might contribute to the various disruptions in sleep.
Snoring and Sleep Apnea
Snoring is simply a sound produced by the vibration of soft tissues in the nose, throat, and mouth. It occurs nearly universally. However, it may also be associated with conditions that narrow the upper airway. These may include:
- obesity
- nasal congestion
- malformation of the skull or face (including abnormal jaw position or size and narrow nasal cavities)
- hypothyroidism
- acromegaly
- tonsil or adenoid enlargement
In severe cases, snoring may also coexist with complete cessation of breathing called obstructive sleep apnea. This condition is common and may be seen in those with the above abnormalities. In addition, it is more prevalent in men and older adults. Other risk factors include: heredity, smoking (which makes sleep apnea three times as common), and increased neck circumference.
Some individuals may suffer from central sleep apnea, which is a failure of the brain to stimulate breathing while one is asleep. Heart failure is the most common cause. It can also be caused by problems with the central nervous system, neuromuscular disease, or with severe abnormalities in the process of breathing. It can also occur in healthy individuals at sleep onset.
Insomnia
There are numerous potential causes of insomnia, which is the most common of the sleep disorders. These causes may include:
- stress
- poor sleep habits
- medications
- caffeine or stimulant use
- drug use
- other medical or psychiatric conditions
- idiopathic or unrecognized causes
Parasomnias
Parasomnias are undesirable actions or experiences which occur "around sleep." They may appear purposeful, but the individual typically has no conscious awareness or recollection of the events. These may include sleepwalking, sleep terrors, sleep paralysis, and REM sleep behavior disorders (in which a person acts out his or her dreams). In general, the cause of these disorders is not entirely understood but some potential causes include medications, drug use, and other medical or psychiatric conditions. For example, REM sleep behavior disorder seems to be associated with Parkinson's disease, but the mechanism is not understood.
Sleep Paralysis
Sleep paralysis is believed to be a problem with the regulation of REM sleep. During this phase of sleep, the body is kept relaxed so that dreams are not acted out. If this relaxation (or atonia) occurs while the person is awake, it can cause temporary paralysis. This may be experienced when a REM period is disrupted. How this occurs is not fully understood at this time, but it is relatively common.
Restless Legs Syndrome
The cause of primary restless legs syndrome (RLS) is not known. It does tend to run in families, suggesting a genetic basis. One hypothesis is that RLS results from problems with cells in part of the brain called the hypothalamus. These cells are believed to produce a neurotransmitter called dopamine for the spinal cord. Neurotransmitters are chemicals that serve to transmit signals between nerve cells. Another neurotransmitter called hypocretin interacts with dopamine and may be increased in individuals with RLS. Iron metabolism within the brain may also play a role.
RLS may also be secondary to other medical conditions or problems, including:
- iron deficiency
- uremia as seen in end-stage kidney disease
- diabetes mellitus
- rheumatic disease
- venous insufficiency
- multiple sclerosis
- Parkinson's disease
- pregnancy
Other potential causes include: peripheral neuropathies, vitamin deficiencies, lumbosacral radiculopathy (low back nerve damage), spinal stenosis, excessive caffeine intake, hypoglycemia (low blood sugar), and hypothyroidism.
Circadian Rhythm Disorders
The circadian rhythm disorders result from a misalignment between the environment and an individual's sleep-wake cycle. These disorders may include advanced or delayed sleep phase disorders, shift work sleep disorder, or jet lag. There may be clearly apparent causes, such as working night shifts or traveling across time zones. In addition, blind individuals may have significant circadian rhythm problems. However, other potential causes are not well-established.
Narcolepsy
In general, there are three potential causes of narcolepsy: loss of signaling by the neurotransmitter called orexin, genetic factors, and rare brain lesions.
Orexin (or hypocretin) is normally produced in a part of the brain called the lateral hypothalamus. It acts to increase the activity of many brain regions and promotes wakefulness. It is thought that this prevents inappropriate transitions into sleep. It also inhibits REM sleep and its loss may allow cataplexy, hypnagogic hallucinations, and sleep paralysis to occur during wakefulness. Individuals with narcolepsy with cataplexy have loss of the neurons that produce orexin and little to none of it is detectable in their spinal fluid. The cause of narcolepsy without cataplexy is unknown.
There does seem to be a genetic influence to narcolepsy, but environmental factors appear to be even more important. Loss of orexin neurons may be due to autoimmune or inflammatory processes, though the evidence for this is mixed. In addition, narcolepsy may rarely be due to lesions in the posterior hypothalamus and midbrain. These lesions may include tumors, abnormal blood vessels, and strokes and may result in secondary narcolepsy. It may occur with genetic syndromes such as Prader-Willi syndrome and Niemann-Pick disease.
Chronic Fatigue Syndrome
The cause of chronic fatigue syndrome (CFS) is not clearly understood, but it may result from multiple unrelated causes.
Although similar to various acute or chronic infections, it seems clear that CFS is not due to any single infectious disease. Another hypothesis is that the immune system, which is used to fight infection, may play a role in developing CFS. Findings that would typically occur in this situation have not been observed, however. Some research has investigated the role of the hypothalamic-pituitary-adrenal (HPA) axis, which can alter cortisol and other hormones that affect the immune system and other body functions. This research has been largely inconclusive. Finally, there is no evidence that vitamin deficiencies cause CFS.
Jet Lag
The cause of jet lag is a lack of synchrony between body rhythms including sleep cycles and hormone patterns and the environment. This often is caused by rapid travel across time zones, with increased symptoms corresponding to a greater number of time zones crossed.
Seasonal Affective Disorder
The cause of seasonal affective disorder (SAD) is not well understood. It may result when decreased light is available in the fall and winter, triggering depression in those predisposed to it. This may relate to abnormal melatonin metabolism or changes in the circadian rhythm, but the evidence for these causes is inconsistent. SAD may also be caused by abnormally low levels of the neurotransmitter called serotonin.
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