Narcolepsy is a chronic neurological disorder that impairs the ability to regulate sleep–wake cycles, and specifically impacts REM (rapid eye movement) sleep. The symptoms of narcolepsy include excessive daytime sleepiness (EDS), sleep-related hallucinations, sleep paralysis, disturbed nocturnal sleep (DNS), and cataplexy. People with narcolepsy typically have poor quality of sleep. There are two recognized forms of narcolepsy: type 1 and type 2. Narcolepsy type 1 features EDS with either cataplexy or cerebrospinal fluid (CSF) orexin levels of less than 110 pg/ml, but most cases present with both. Cataplexy appears as transient episodes of aberrant muscle tone (typically loss of muscle tone) triggered by strong emotion. In pediatric-onset narcolepsy, cataplexy can present with transient hyperkinetic features. Cataplexy may be mistaken for syncope, tics, or seizures. Narcolepsy type 2 (NT2) does not feature cataplexy, and CSF orexin levels are normal. Sleep-related hallucinations, both hypnagogic (going to sleep) and hypnopompic (on awakening), can be auditory, visual, or tactile and may occur independently of or in combination with an inability to move (sleep paralysis). Narcolepsy is a clinical syndrome of hypothalamic disorder, but the exact cause of narcolepsy is unknown, with potentially several causes. A leading consideration for the cause of narcolepsy type 1 is that it is an autoimmune disorder. Proposed pathophysiology as an autoimmune disease suggest antigen presentation by DQ0602 to specific CD4+ T cells resulting in CD8+ T-cell activation and consequent injury to orexin producing neurons. Relative risk for narcolepsy in a first-degree relative is considered to be at least 10 times higher than the general population, Having multiple relatives with a primary sleep disorder significantly increases the relative risk but absolute risk still remains low due to the rarity of the condition. The autoimmune process is thought to be triggered in genetically susceptible individuals by an immune-provoking experience, such as an infection with H1N1 influenza. Secondary narcolepsy can occur as a consequence of another neurological disorder. Secondary narcolepsy can be seen in some individuals with traumatic brain injury, tumors, Prader–Willi syndrome or other diseases affecting the parts of the brain that regulate wakefulness or REM sleep. Diagnosis is typically based on the symptoms and sleep studies, after excluding alternative causes of EDS. EDS can also be caused by other sleep disorders such as insufficient sleep syndrome, sleep apnea, major depressive disorder, anemia, heart failure, and drinking alcohol. While there is no cure, behavioral strategies, lifestyle changes, social support, and medications may help. Lifestyle and behavioral strategies can include identifying and avoiding or desensitizing emotional triggers for cataplexy, dietary strategies that may reduce sleep-inducing foods and drinks, scheduled or strategic naps, and maintaining a regular sleep-wake schedule. Social support, social networks, and social integration are resources that may lie in the communities related to living with narcolepsy. Medications used to treat narcolepsy primarily target EDS and/or cataplexy. These medications include alerting agents (e.g., modafinil, armodafinil, pitolisant, solriamfetol), oxybate medications (e.g., twice nightly sodium oxybate, twice nightly mixed oxybate salts, and once nightly extended-release sodium oxybate), and other stimulants (e.g., methylphenidate, amphetamine). There is also the use of antidepressants such as tricyclic antidepressants, selective serotonin reuptake inhibitors (SSRIs), and serotonin–norepinephrine reuptake inhibitors (SNRIs) for the treatment of cataplexy.
Estimates of frequency range from 0.2 to 600 per 100,000 people in various countries. The condition often begins in childhood, with males and females being affected equally. Untreated narcolepsy increases the risk of motor vehicle collisions and falls. Narcolepsy generally occurs anytime between early childhood and 50 years of age, and most commonly between 15 and 36 years of age. However, it may also rarely appear at any time outside of this range.
Signs and symptoms There are two main characteristics of narcolepsy: excessive daytime sleepiness and abnormal REM sleep. Excessive daytime sleepiness occurs even after adequate night time sleep. A person with narcolepsy is likely to become drowsy or fall asleep, often at inappropriate or undesired times and places, or just be very tired throughout the day. Narcoleptics may not be able to experience the amount of restorative deep sleep that healthy people experience due to abnormal REM regulation – they are not "oversleeping." Narcoleptics typically have higher REM sleep density than non-narcoleptics, but also experience more REM sleep without atonia. Many narcoleptics have sufficient REM sleep, but do not feel refreshed or alert throughout the day. Excessive sleepiness can vary in severity and appears most commonly during monotonous situations that require little interaction. Daytime naps may occur with little warning and may be physically irresistible. These naps can occur several times a day. They are typically refreshing, but only for a brief period. Vivid dreams may be experienced regularly, even during short naps. Drowsiness may persist for prolonged periods or remain constant. Additionally, nighttime sleep may be fragmented, with frequent awakenings. A second prominent symptom of narcolepsy is abnormal REM sleep. Narcoleptics are unique in that instead of following the typical sleep cycle, they enter into the REM phase of sleep at the beginning of sleep, even when sleeping during the day. The classic symptoms of the disorder, often referred to as the "tetrad of narcolepsy", are cataplexy, sleep paralysis, hypnagogic hallucinations, and excessive daytime sleepiness. Other symptoms include automatic behaviors and night-time wakefulness. These symptoms may not occur in all people with narcolepsy.
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