Causes of excessive daytime sleepiness
- Narcolepsy
- Insufficient sleep at night
- Sleep apnea
- Circadian rhythm disorders such as jet lag and advanced and delayed
sleep phase syndrome
- Idiopathic hypersomnolence
- Periodic limb movement disorder—clues include restless legs
in the evening, repetitive limb movements in sleep
- Depression
- Head injury
- Other medical disorders, e.g., chronic pain disturbing sleep
- Drugs
Very rarely, narcolepsy can be symptomatic of another underlying disorder
of the central nervous system, usually a structural lesion involving the
region of the hypothalamus. If this is true, there will probably be additional
symptoms and signs of endocrine or neurological disorder. Occasionally,
epilepsy can be mistaken for narcolepsy, and there have been cases where
patients faked narcolepsy (perhaps to get a prescription for drugs).
It's much more common for the reverse to be true: for narcolepsy to be
undiagnosed. Indeed, some researchers believe as many as three-quarters
of Americans with narcolepsy have not been diagnosed. Narcolepsy is sometimes
diagnosed as epilepsy, chronic fatigue syndrome, and schizophrenia.
How do doctors decide who has clinical excessive daytime sleepiness?
History
Recording of patient histories is the key to the diagnosis of excessive
daytime sleepiness. A structured history is taken. The Epworth sleepiness
scale is often includes in this assessment.
Examination
A physical examination is seldom informative. However, obesity and causes
of upper airway obstruction may be clues to a diagnosis of obstructive
sleep apnoea. Endocrine or neurological signs may point to an underlying
neurological cause of sleepiness (other than idiopathic narcolepsy).
Is the patient genuinely sleepy or just tired? The Epworth sleepiness
scale is a helpful method of quantifying daytime sleepiness.
Is the patient getting regular and sufficient sleep? Check on bed time,
wake time, sleep quality and pattern (for example, shift
work)
Does the patient snore heavily or stop breathing during sleep? If so,
consider obstructive sleep apnoea
Is there a history of short lived weakness on emotional arousal? If
so, consider narcolepsy
Is there a history of uncomfortable, fidgety legs in the evenings? If
so, consider restless legs syndrome
Is there evidence of depression (low mood or lack of pleasure in life)?
If so, excessive daytime sleepiness might be symptomatic of a mood disorder
Might prescribed or recreational drugs be contributing to sleepiness?
Are there other potentially relevant medical conditions disturbing sleep,
such as chronic pain?
Where possible, a history should be taken from the bed partner
Investigations
Investigations need specialist expertise and equipment and are tailored
to the suspected cause of excessive daytime sleepiness. Whether every
patient with suspected narcolepsy needs formal evaluation in a sleep laboratory
is a matter for debate.
Gathering objective data at the outset by using sleep tests is wise.
These tests should include an assessment of overnight sleep quality, typically
with polysomnography, and an evaluation of daytime sleepiness on the following
day, using the multiple sleep latency test. This test offers the patient
four HLA typing and toxicology for amphetamines (in rare cases in which
patients are suspected of simulating narcolepsy to obtain a supply) are
occasionally helpful. Measurement of hypocretin concentrations in cerebrospinal
fluid may become a standard diagnostic tool in narcolepsy, but right now
this technique is used only in research.
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