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- First, we are going to discuss the narcolepsy meaning by defining the neurological disorder.
- We will provide a list of narcolepsy symptoms, highlighting the different types of narcolepsy.
- Then, we will delve into the possible narcolepsy causes.
- Finally, we will discuss the different options for narcolepsy treatment.
Narcolepsy can prompt sudden attacks of sleep throughout the day, freepik.com
Narcolepsy Meaning
Narcolepsy is a long-term neurological sleep disorder that affects the body's natural sleeping patterns. We can define narcolepsy as:
Narcolepsy is a long-term neurological sleep disorder characterised by sudden attacks of sleep at any moment during the day and feelings of drowsiness and exhaustion—those with narcolepsy struggle with maintaining control over their sleep-wake cycle.
Narcolepsy Symptoms and Diagnosing Narcolepsy
For a diagnosis of narcolepsy under the Diagnostic and Statistic Manual of Mental Health Disorders Fifth Edition (DSM-5), a person must be showing:
- A reoccurring need to sleep (napping) that is almost impossible to ignore, which occurs multiple times during the same day
- A reoccurring need to sleep that lasts for over three months and occurs at least three times or more a week
- At least one other symptom:
- Cataplexy
- Hypocretin deficiency
- REM sleep latency equal to or above 15 minutes on nocturnal polysomnography (PSG)
- Mean sleep latency that is equal to or above eight minutes on multiple sleep latency testing (MSLT)². The test is used to measure the scale of sleepiness during the daytime.
Cataplexy is a state of muscle paralysis where muscle tone and control over muscles are lost, usually induced by strong emotions.
Hypocretin (orexin) is a neuropeptide that influences wakefulness, arousal, and other essential functions and is secreted from the hypothalamus.
More apparent symptoms that a person is suffering from narcolepsy include:
- Excessive Daytime Sleepiness (EDS) - a person with narcolepsy may feel exhausted throughout the day, often falling asleep without much warning during the daytime
- Cataplexy - muscle paralysis, usually occurring in the REM stage of sleep; cataplexy can present itself suddenly during the day in those with narcolepsy, resulting in the person losing control over their muscles. Cataplexy also occurs when feeling strong emotions that prompt laughing bouts, for example.
- Hypnagogic (falling asleep)/Hypnopompic (waking up) Hallucinations - those with narcolepsy may hallucinate and see things that are not there and have vivid dreams. These result in difficulty separating dreams from reality when coupled with hallucinations.
- Sleep paralysis - after falling asleep and waking up, people with narcolepsy may experience episodes of sleep paralysis, a state of being unable to move and speak, and people often report experiencing vivid dreams or hallucinations during episodes of sleep paralysis.
- Abnormal REM cycle - REM (rapid eye movement) sleep may begin a lot earlier in those with narcolepsy compared to a regular sleep-wake cycle, often beginning moments after the person has officially fallen asleep.
For exam purposes, you only need to know about EDS, Cataplexy, Hallucinations, Sleep Paralysis, and Abnormal REM states. It helps to remember how narcolepsy is diagnosed, however!
Narcolepsy can result in EDS, excessive daytime sleepiness, freepik.com
Susan walks to work and feels very tired throughout the journey. When she arrives at her workplace and sits down at her desk, her coworkers come to greet her.
One coworker tells Susan a funny joke, and Susan laughs but suddenly loses muscle control and falls asleep.
Susan struggles with exhaustion throughout the day, and when she finally gets home and goes to bed, as she falls asleep, she sees a figure of a woman standing in the corner of her room. Susan cannot move or speak, and when she falls asleep, she has a vivid dream that is hard to separate from reality.
Susan has been experiencing these symptoms and scenarios for four months ongoing now.
A professional may diagnose Susan with narcolepsy.
Different Types of Narcolepsy
There are two types of narcolepsy we can define. They differ in terms of symptoms:
- Type 1: With cataplexy/low levels of hypocretin
- Type 2: Without cataplexy
Type 1 reports cataplexy and/or low levels of hypocretin, whereas type 2 reports excessive drowsiness during the day but no muscle control loss and normal levels of hypocretin. Type 1 is more common than type 2, with most people reporting some form of cataplexy with their narcolepsy.
Narcolepsy causes
Narcolepsy causes and explanations include deficiency of hypocretin (the neuropeptide we discussed above), genetic heritability, stress and lifestyle influences, and evolutionary influences.
Hypocretin Deficiency
Hypocretin, also known as orexin, is a neuropeptide produced in the lateral hypothalamus that exerts control over certain bodily functions, notably wakefulness.
The sleep-wake cycle is a circadian rhythm that acts as a biological clock for the human body. It is regulated by various systems, including neurotransmitters and brain structures such as the hypothalamus.
Hypocretin is important in keeping you awake when you're low on sleep and intend to stay awake and is also a key factor in staving off and regulating REM sleep.
When damage or loss of the cells producing hypocretin occurs, causing a deficiency in hypocretin, it results in EDS and, ultimately, narcolepsy.
Hypocretin levels are usually measured by taking a sample of cerebrospinal fluid.
Nishino et al. (2000) investigated hypocretin deficiency in humans with narcolepsy.
Previous research on the subject often used knockout mice, mice who had undergone gene replacement.
They hypothesised that hypocretin transmission disruption would cause narcolepsy in humans. They measured hypocretin levels in nine participants with diagnosed narcolepsy (type 1) and eight controls.
Those with narcolepsy were HLA (human leukocyte antigen) positive. We will cover more on HLA when we discuss genetics.
Nishino et al. (2000) found deficient hypocretin neurotransmission in those with narcolepsy. The findings suggest that hypocretin deficiency is associated with and contributes to the development of narcolepsy.
Genes
The human leukocyte antigen (HLA) is associated with narcolepsy, suggesting there is a genetic component to narcolepsy. HLA is associated with an autoimmune attack on hypocretin-producing neurons in the hypothalamus resulting in the loss of these cells, as we mentioned above.
It is important to note, however, that although around 90-95% of those with type 1 narcolepsy are HLA positive (specifically HLA-DQB1*0602, this is a very technical term that you do not need to know for your exams), it does not mean that all people HLA-DQB1*0602 positive have narcolepsy with cataplexy. So, we cannot use it as a clear-cut tool to diagnose the disorder (Guilleminault & Abad, 2009).
As well as associations with the HLA complex, family members are 20–40 times at an increased risk for the disorder if diagnosed in a first-degree relative (Chabas et al., 2003).
Stress and Lifestyle
Stress is associated with narcolepsy, as narcolepsy is largely affected by emotions. Strong emotions tend to trigger narcoleptic episodes, such as anger and laughter.
Specific brain regions have been associated with narcolepsy, specifically the amygdala, and the effects of laughter (Meletti et al., 2015).
Animal studies have found that disruption in regulating hypocretin-producing systems is associated with mood disorders, particularly depression and anxiety (Yeoh et al., 2014).
Stress can affect narcolepsy, freepik.com
Evolution
Certain animals have a tonic immobility response to stress. What we mean by this is that, upon being faced by a predator or a situation where running may cause more harm than good, some animals still go and undergo a form of muscle paralysis.
When caught by a cat, a bird may undergo tonic immobility until the cat grows bored or complacent, and then the bird will try to escape.
Some animals may play dead altogether. Both options increase the chances of the animal blending into its environment.
Evolution could suggest muscle paralysis is a survival trait in specific scenarios.
Narcolepsy treatment
Narcolepsy cannot be cured at the moment, unfortunately, but we can try to manage the symptoms via:
- Adopting good sleep hygiene habits
- Taking planned naps throughout the day
- Exercise
- Medications such as modafinil (a stimulant) and antidepressants
- Speaking with others, especially if cataplexy is proving particularly problematic (others can assist if affecting daily life)
- Meditation and therapies to cope with vivid dreams
Narcolepsy - Key takeaways
- Narcolepsy is a long-term neurological sleep disorder characterised by sudden attacks of sleep at any moment during the day and feelings of drowsiness and exhaustion—those with narcolepsy struggle with maintaining control over their sleep-wake cycle.
- There are two types of narcolepsy: type 1 (with cataplexy) and type 2 (without cataplexy). Cataplexy is the loss of muscle control and tone, causing paralysis. Strong emotions usually trigger narcoleptic episodes, such as laughter or anger.
- Symptoms of narcolepsy include excessive daytime sleepiness (EDS), hallucinations and vivid dreams, cataplexy, abnormal REM sleep, and sleep paralysis.
- There are multiple explanations for narcolepsy, including deficiency in hypocretin (a neuropeptide produced by cells in the lateral hypothalamus), genetic explanations (HLA), stress and lifestyle issues, and evolutionary advantages.
- Narcolepsy can be treated by practising good sleep hygiene habits, planned naps throughout the day, exercise, medications such as modafinil and antidepressants, speaking with others and having support systems and therapies to cope with vivid nightmares.
References
- Ruoff, C., & Rye, D. (2016). The ICSD-3 and DSM-5 guidelines for diagnosing narcolepsy: clinical relevance and practicality. Current Medical Research and Opinion, 32(10), 1611-1622.
- Nishino, S., Ripley, B., Overeem, S., Lammers, G. J., & Mignot, E. (2000). Hypocretin (orexin) deficiency in human narcolepsy. The Lancet, 355(9197), 39-40.
- Christian Guilleminault, Vivien C. Abad, in Sleep Disorders Medicine (Third Edition), 2009
- Chabas, D., Taheri, S., Renier, C., & Mignot, E. (2003). The genetics of narcolepsy. Annual review of genomics and human genetics, 4(1), 459-483.
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Frequently Asked Questions about Narcolepsy
What is narcolepsy?
Narcolepsy is a long-term neurological sleep disorder characterised by sudden attacks of sleep at any moment during the day and feelings of drowsiness and exhaustion—those with narcolepsy struggle with maintaining control over their sleep-wake cycle.
What causes narcolepsy?
Causes of narcolepsy include hypocretin deficiency (due to loss or damage to hypocretin-producing neurons in the lateral hypothalamus), genes (HLA), stress and lifestyle choices, and evolutionary advantages to muscle paralysis.
What are the 5 signs of narcolepsy?
Signs of narcolepsy include:
- Excessive daytime sleepiness (EDS)
- Hallucinations and vivid dreams
- Cataplexy
- Sleep paralysis
- REM sleep latency abnormalities
Is narcolepsy a mental illness?
Narcolepsy is a long-term neurological sleep disorder.
How to prevent narcolepsy?
Practising good sleep hygiene habits, exercising, and taking planned naps can help prevent episodes of narcolepsy.
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