It’s a lifelong disorder that affects 1 out of 2,000 people worldwide.
For most individuals, symptoms of narcolepsy present in the late teenage years or early twenties, typically before the age of 25. There are no differences in rates of narcolepsy among men and women.
Narcolepsy is caused by a deficiency of a hormone called hypocretin (also called “orexin”). This hormone is found in the hypothalamus in the brain and functions as a regulator of sleep and wakefulness.
Reduction of orexin, or deficiency of orexin, causes the typical symptoms of narcolepsy.
- Excessive daytime sleepiness
- Sleep paralysis
- Hypnogogic hallucinations (vivid, dream-like images that occur at the onset of sleep)
Where individuals are totally deficient of orexin, they develop the most disabling symptom of narcolepsy: cataplexy. This involves the sudden loss of muscle tone in response to emotional stimuli.
Who gets narcolepsy?
Narcolepsy isn’t a familial condition, i.e. you don’t inherit it.
The current understanding of the cause of narcolepsy is that there may be a viral or immunological mechanism that causes the destruction of the orexin-producing cells in the hypothalamus, resulting in the symptoms of narcolepsy.
Orexin (or hypocretin) is a hormone that functions as a regulator of sleep and wakefulness in the brain.
Narcolepsy is a lifelong disorder that affects 1 out of 2,000 people worldwide. In Japan, it’s thought to be much more common, affecting 1 in 600 people.
What are the symptoms of narcolepsy?
The four classic symptoms of narcolepsy are:
- Excessive daytime sleepiness.
- Sleep paralysis: paralysis upon falling asleep or waking up.
- Hypnagogic hallucinations: vivid dream-like images that occur at the onset of sleep.
- Cataplexy: sudden, brief episodes of muscle weakness or paralysis brought on by strong emotions such as laughter, anger, surprise or anticipation.
Disturbed night-time sleep, including tossing and turning in bed, leg jerks, nightmares and frequent awakenings, may also occur. The development, number and severity of symptoms of narcolepsy vary widely among individuals with the disorder. Unrelenting, excessive sleepiness is usually the first and most prominent symptom of narcolepsy.
The American Academy of Sleep Medicine (AASM) recently classified narcolepsy into two types based on the presence (Na-1) or absence (Na-2) of cataplexy. Excessive daytime sleepiness (EDS), hypnogogic hallucinations and sleep paralysis are present in both Na-1 and Na-2.
The symptoms in greater detail
Cataplexy is more accurately described as a sudden loss of muscle tone while the person is awake, leading to feelings of weakness and a loss of voluntary muscle control.
Episodes of cataplexy develop over several seconds, and individuals remain entirely conscious – a feature that differentiates these episodes from seizures – regardless of the varying duration and intensity that have been reported. The severity of cataplexy episodes range from mild weakness of facial muscles (e.g. drooping of an eyelid) to a complete loss of tone in voluntary muscles, resulting in collapsing to the floor.
Excessive daytime sleepiness (EDS), the cardinal feature of narcolepsy, is also typically the first presenting symptom. EDS is regularly accompanied by sleep attacks, which are abrupt, involuntary sleep episodes lasting anywhere from a few seconds to several minutes.
People with the disorder experience irresistible sleep attacks throughout the day, which can last for 30 seconds to more than 30 minutes, regardless of the amount or quality of prior night-time sleep. These attacks result in episodes of sleep at work and social events, while eating, talking and driving, and in other similarly inappropriate settings.
Sleep paralysis is described as “the disturbing temporary inability to move voluntary muscles at sleep-wake transitions, usually occurring at the point of waking and less often at the point of falling asleep”.
Hypnogogic hallucinations refers to dream-like images that occur on sleep onset. It reflects an abnormality of sleep cycles found in people with narcolepsy. Affected individuals tend to go straight into rapid eye movement (REM) sleep.
People with narcolepsy also have substantial fragmentation of their night-time sleep, which reduces the quality of sleep. This increases the severity of daytime symptoms.
What causes narcolepsy?
Narcolepsy is caused by a total or partial deficiency of a hormone called hypocretin (orexin). This hormone is found in the hypothalamus – a small region in the centre of the brain.
Orexin is thought to play an important role in the regulation of sleep and arousal states. Low or undetectable levels of the hormone is found in most people with narcolepsy.
Interestingly, there may also be involvement of this hormone in other disorders of sleep such as insomnia.
What are the risk factors for narcolepsy?
The exact cause for the deficiency of orexin (hypocretin) hasn’t been identified (remember: narcolepsy is caused by a total or partial deficiency of this hormone).
However, potential risk factors include:
- A set of DNA variations (the HLA DR2 haplotype). This suggests that the condition may potentially result from an autoimmune process – a process in which the body's immune system attacks and destroys body tissue that it mistakes for foreign matter.
- A loss in hypothalamic neurons containing the neuropeptide, hypocretin, is strongly associated with Na-1 (formerly known as narcolepsy with cataplexy).
- Environmental factors such as flu infections, unexplained fevers, major changes in sleeping habits, strokes, tumours and traumatic brain injuries (TBIs) have also been found to be related to narcolepsy.
- More recently, immunisation with the H1N1 flu vaccine appears to have triggered narcolepsy in a significant proportion of recipients.
What is the course and prognosis of narcolepsy?
Although narcolepsy is a life-long condition, most people with the disorder enjoy a near-normal lifestyle with adequate medication and support from teachers, employers and family members.
If it isn’t properly diagnosed and treated, narcolepsy may have a devastating impact on the life of the affected individual, causing social, educational, psychological and financial difficulties.
There is presently no cure for narcolepsy. However, the symptoms can be controlled with behavioural and medical therapy.
How is narcolepsy diagnosed?
Narcolepsy is diagnosed by means of a comprehensive clinical interview combined with sleep studies that measure the physiology of night-time sleep. A test called a nocturnal polysomnography (NPSG) is done in a sleep laboratory and electronically records specific physical activities while you sleep.
The NPSG is usually followed by a daytime test of sleepiness – a multiple sleep latency test (MSLT). This test measures how quickly you fall asleep during the day and monitors how quickly and how often you enter REM (rapid eye movement) sleep.
How is narcolepsy treated?
Treatment of narcolepsy is geared toward three elements:
- Excessive daytime sleepiness. This is usually treated with wake-promoting agents (such as modafinil) or stimulants (e.g. methylphenidate or amphetamines).
- Cataplexy (for Na-1). The usual medications used for cataplexy are classed as antidepressants: tricyclics, SSRIs (e.g. Prozac) or SNRIs (e.g. venlafaxine).
- Disturbed night-time sleep: This is usually treated as one would treat insomnia, i.e. with a short course of hypnotics (Z-drugs or benzodiazepines) combined with cognitive behavioural techniques.
Medications are quite successful in treating the majority of people with narcolepsy. In a small group with severe intractable cataplexy, sodium oxybate is now licensed for use.
Basic lifestyle adjustments – such as regulating your sleep schedules, taking scheduled daytime naps, and avoiding “over-stimulating” situations – may also help to reduce the intrusion of symptoms into daytime activities.
Narcolepsy: when to visit your doctor
If you’ve developed symptoms of excessive daytime sleepiness that have persisted for more than one month, you need to seek specialist help.
If you find that you’re experiencing muscle weakness or collapsing episodes triggered by a response to emotional stimulation (for example laughing, getting surprised, getting upset), you need to seek help immediately
Reviewed by Dr Irshaad Ebrahim, specialist neuropsychiatrist in sleep disorders at The London Sleep Centre and The Constantia Sleep Centre. FRCPsych. April 2018.