Causes And Symptoms Of Narcolepsy

  • Freya Norris Biological Sciences, University of Birmingham

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Introduction

Narcolepsy is a neurological sleeping disorder that is often misunderstood and misrepresented. It significantly impacts the lives of those affected, commonly causing individuals to fall asleep during the day. This disorder is characterised by excessive daytime sleepiness, sudden loss of muscle tone, hallucinations, and disrupted sleep during the night.

Narcolepsy poses challenges to regular daily functioning and impacts one’s quality of life. However, there is currently no cure for the disorder. In this article, we will delve into the causes and symptoms of narcolepsy, shedding light on the complexities of this condition. We will also explore available options to help manage narcolepsy symptoms.

What are narcolepsy symptoms?

Narcolepsy manifests through a variety of symptoms which significantly impact daily life and vary in severity among affected individuals. Symptoms first emerge during adolescence or early adulthood and can worsen over time. These include:

Excessive daytime sleepiness (EDS)

EDS (also known as hypersomnia) is the hallmark symptom of narcolepsy, whereby an individual will fall asleep without any warning, regardless of the prior night’s sleep. The resultant sleep lasts between a few minutes to half an hour. These daytime sleep episodes can occur during a task, and the individual may continue with the task in their sleep. This is particularly dangerous if, for instance, an individual is driving.

Sudden loss of muscle tone (cataplexy)

Cataplexy refers to a sudden and temporary loss of muscle tone triggered by emotions, such as laughter, excitement, or anger.1 It can range from mild muscle weakness to complete muscle collapse, resembling a form of paralysis. Narcolepsy is classified into two types according to the presence of cataplexy:

  • Narcolepsy type 1 (narcolepsy with cataplexy)
  • Narcolepsy type 2 (narcolepsy without cataplexy)

Changes in REM sleep

Rapid eye movement (REM) sleep is when most dreaming happens. Individuals with narcolepsy tend to enter REM sleep within 15 minutes of falling asleep, compared to the 60 to 90 minutes it takes for those without narcolepsy.2 REM sleep can happen at any time of the day.

Sleep paralysis

Sleep paralysis consists of a temporary inability to move or speak while falling asleep or waking up. It is usually accompanied by vivid hallucinations and a sense of impending danger, contributing to distress and anxiety. Sleep paralysis occurs due to the disruption of normal REM sleep mechanisms, leading to the persistence of muscle atonia (loss of muscle control) beyond the REM sleep phase. However, not everyone who experiences sleep paralysis has narcolepsy.

Hallucinations

Also referred to as excessive dreaming, hallucinations can occur while falling asleep (hypnagogic hallucinations) or as you are waking up (hypnopompic hallucinations). Hallucinations are often vivid and may involve visual, auditory, or tactile sensations. These hallucinations result from the intrusion of REM sleep into wakefulness, blurring the boundaries between sleep and wake states.

What causes narcolepsy?

Narcolepsy is a chronic neurological disorder affecting the brain's ability to regulate its sleep-wake cycles. Despite being recognised as a disorder for over a century, its causes are not entirely understood. However, recent research has unveiled several factors contributing to its development.

Neurotransmitter imbalance

Neurotransmitters are chemical messengers that transmit messages through nerves in the body. Narcolepsy involves a dysregulation of neurotransmitter systems, notably hypocretin (also known as orexin). Hypocretin plays a crucial role in promoting wakefulness and regulating REM sleep.3 Emerging evidence suggests autoimmune mechanisms are involved in the destruction of neurons producing hypocretin in narcolepsy. This leads to a hypocretin deficiency, which may cause dysregulation of sleep. 

Genetic predisposition

Studies have identified a strong genetic component in narcolepsy. Specific gene variations associated with the immune system, such as the HLA-DQB1*06:02 variation, have been linked to an increased risk of narcolepsy. There is also direct evidence of familial aggregation of narcolepsy.4 However, genes are not the sole determinant of whether an individual has narcolepsy. 

Autoimmune dysfunction

As mentioned above, emerging evidence implicates autoimmune mechanisms in the development of narcolepsy. This occurs when your immune system mistakenly attacks neurons responsible for the production of hypocretin. Autoimmune responses can be triggered by environmental factors, such as viral and bacterial infections or certain vaccinations. Many individuals suffer from narcolepsy after being infected with the H1N1 influenza virus or the bacteria causing strep throat, both of which trigger changes in the immune system.5

Brain injuries

In rare cases, narcolepsy can be triggered by traumatic brain injury, including a concussion. One study reported that around 6% of those who had suffered a traumatic brain injury were diagnosed with narcolepsy.6

Narcolepsy risk factors

Risk factors associated with narcolepsy include:

Age

Narcolepsy usually emerges between 10 and 30 years.

Gender

Studies suggest that, although people assigned male at birth (AMAB) and female at birth (AFAB) are equally likely to suffer from narcolepsy, people AFAB tend to receive a later diagnosis. The impact of narcolepsy may also vary due to differences in health and lifestyle.7

Family history

Your risk of developing narcolepsy is 20 to 40 times higher if you have a close family member suffering from the disorder.

Diagnosing narcolepsy

Narcolepsy diagnosis is carried out by healthcare professionals and involves a combination of medical history evaluation, physical examination, and sleep studies.

Medical history

The doctor will ask about your symptoms, sleep patterns, and other relevant medical history. 

Physical examination

A physical exam may be conducted to rule out other conditions that could be causing your symptoms.

Sleep diary

Keeping a sleep diary for a few weeks can provide valuable information about your sleep patterns and daytime alertness.

Sleep test (polysomnography)

This test is usually conducted overnight in a sleep centre. It involves monitoring various parameters while you sleep, including:

  • Brain activity
  • Eye movements
  • Muscle tone
  • Heart rate
  • Breathing patterns

This test assesses sleep quality and helps diagnose conditions like sleep apnoea.

Multiple sleep latency test (MSLT)

This test is often performed the day after a polysomnography. It measures how quickly you fall asleep and whether you enter REM sleep during scheduled daytime naps. People with narcolepsy tend to fall asleep quickly and enter REM sleep early during these naps.

Hypocretin level testing

In some cases, a lumbar puncture (spinal tap) may be done to measure the levels of hypocretin in your cerebrospinal fluid. As discussed earlier, low levels of hypocretin are associated with narcolepsy.

The diagnosis of narcolepsy can be challenging because its symptoms often overlap with other sleep disorders and medical conditions. Therefore, it is essential to consult a healthcare professional experienced in sleep medicine to undergo a proper evaluation and obtain an accurate diagnosis.

Treating narcolepsy

Narcolepsy is incurable. Nonetheless, there are various options available to alleviate symptoms. Narcolepsy treatment typically involves a combination of medications and lifestyle adjustments to manage symptoms and improve daily functioning. Here are some of the common treatment approaches:

Stimulant medications

These medications help to reduce EDS and improve alertness. Examples include modafinil (Provigil) and armodafinil (Nuvigil).

Sodium oxybate (Xyrem)

This medication is usually taken at night, improving night sleep and reducing daytime sleepiness.8

Selective serotonin reuptake inhibitors (SSRIs) or Serotonin-norepinephrine reuptake inhibitors (SNRIs)

These antidepressants can help regulate REM sleep and improve symptoms like cataplexy.

Wake-promoting agents

Medications such as pitolisant (Wakix) work differently from traditional stimulants and may be an option for those who don't respond well to other medications.

Lifestyle changes

Practices, such as having a regular sleep schedule, scheduling naps, and avoiding alcohol or caffeine close to bedtime can help manage narcolepsy symptoms.

Cognitive behavioural therapy (CBT)

CBT can help address psychological aspects of narcolepsy, such as anxiety or depression, which exacerbate symptoms.

Supportive therapies

Support groups and counselling can provide emotional support and coping strategies for managing narcolepsy in daily life.

Individuals with narcolepsy should work closely with healthcare professionals to find the most effective treatment plan for their needs and symptoms. Regular follow-ups and adjustments to treatment may be necessary to optimise the management of the condition.

Summary

Narcolepsy remains a complex and intriguing neurological disorder, characterised by a diverse array of symptoms and underlying mechanisms. While significant progress has been made in unravelling its causes and symptoms, many questions remain unanswered.

Further research into the genetic, immunological, and neurobiological aspects of narcolepsy will be essential for developing targeted interventions and improving the management of this condition. In the meantime, raising awareness and fostering understanding of narcolepsy within society are crucial steps towards supporting affected individuals and promoting their well-being.

References

  1. Burgess CR, Scammell TE. Narcolepsy: neural mechanisms of sleepiness and cataplexy. J Neurosci [Internet]. 2012 Sep 5 [cited 2024 Jun 13];32(36):12305–11. Available from: https://www.jneurosci.org/content/32/36/12305 
  2. Dauvilliers Y, Rompré S, Gagnon JF, Vendette M, Petit D, Montplaisir J. Rem sleep characteristics in narcolepsy and rem sleep behavior disorder. Sleep [Internet]. 2007 Jul 1 [cited 2024 Jun 13];30(7):844–9. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1978363/ 
  3. Mahoney CE, Cogswell A, Koralnik IJ, Scammell TE. The neurobiological basis of narcolepsy. Nat Rev Neurosci [Internet]. 2019 Feb [cited 2024 Jun 13];20(2):83–93. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6492289/ 
  4. Chen L, Fong SYY, Lam CW, Tang NLS, Ng MHL, Li AM, et al. The familial risk and hla susceptibility among narcolepsy patients in hong kong chinese. Sleep [Internet]. 2007 Jul 1 [cited 2024 Jun 13];30(7):851–8. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1978371/ 
  5. Brown C. H1N1 vaccine and narcolepsy link discovered. CMAJ [Internet]. 2015 Sep 8 [cited 2024 Jun 13];187(12):E371. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4562845/ 
  6. Verma NP, Jayakar AV. Traumatic brain injuries and sleep/wake disorders. In: Traumatic Brain Injury [Internet]. IntechOpen; 2014 [cited 2024 Jun 13]. Available from: https://www.intechopen.com/chapters/45750 
  7. Won C, Mahmoudi M, Qin L, Purvis T, Mathur A, Mohsenin V. The impact of gender on timeliness of narcolepsy diagnosis. Journal of Clinical Sleep Medicine [Internet]. 2014 Jan 15 [cited 2024 Jun 13];10(01):89–95. Available from: http://jcsm.aasm.org/doi/10.5664/jcsm.3370 
  8. Dominguez A, Soca Gallego L, Patel P, Parmar M. Sodium oxybate. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 [cited 2024 Jun 13]. Available from: http://www.ncbi.nlm.nih.gov/books/NBK562283/ 

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This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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