Published April 23, 2020
Revised June 9, 2022
Vetted by Our Medical Advisory Board
If you have IH, narcolepsy, KLS, or another related disorder, you can help provide researchers with vital data by joining the Hypersomnia Foundation’s registry at CoRDS (Coordination of Rare Diseases at Sanford)!
Because current treatments for these disorders are very similar and current research indicates that there may also be significant overlap among them, it is important to address and research them together. For more in-depth information about the classification of hypersomnias, click HERE.
About Narcolepsy Types 1 and 2
What is narcolepsy? There are two different types of narcolepsy, but both share the main symptoms of daytime sleepiness and abnormal features of dream sleep (i.e, rapid-eye-movement, or, REM, sleep), such as sleep-related hallucinations and sleep paralysis. A subgroup of patients (about 1/3), especially among those with narcolepsy type 1, have disrupted nocturnal sleep with many short awakenings. Sleep time across 24 hours is typically normal. The usual age of onset is in the mid-to-late teens, although it can begin in the pre-teens or at a later age, and it is a life-long illness.
Narcolepsy occurs in two forms with different underlying causes: narcolepsy type 1 (which is sometimes called narcolepsy with cataplexy) and narcolepsy type 2 (aka narcolepsy without cataplexy). Narcolepsy type 2 shares some features in common with narcolepsy type 1 and other features in common with idiopathic hypersomnia. The cause of narcolepsy type 2 is currently unknown, but it is not caused by the same problem as narcolepsy type 1.
The remainder of this section refers to narcolepsy type 1. Daytime sleepiness in people with narcolepsy type 1 typically occurs as an irresistible urge to fall asleep – sometimes referred to as a “sleep attack” — at random intervals throughout the waking day. These short bouts of sleep are usually refreshing or ‘restorative’ in quality, as is night-time sleep.
The abnormal features of dream sleep experienced by people with narcolepsy type 1 include hallucinations, sleep paralysis, and cataplexy. Hypnagogic hallucinations are dream-like auditory or visual hallucinations upon falling asleep or dozing. Sleep paralysis is the feeling of being paralyzed (unable to move) upon falling asleep or awakening from sleep. These can both be frightening sensations that can last for several minutes.
Cataplexy is a symptom unique to narcolepsy type 1. It is a sudden loss of muscle tone (for tens of seconds to minutes), which is provoked by emotional situations such as laughter, hearing or telling a joke, fear, or anger. Cataplexy varies greatly in intensity and duration – from a person’s knees buckling or jaw becoming lax briefly, to their eyelids and head drooping (thus, mimicking sleep to an observer), to their falling down and being unable to move for several minutes. Conscious awareness of the environment is preserved in patients during an attack of cataplexy, although it might appear to an observer that the patient has “passed out” or “fainted”.
A substantial proportion of people with narcolepsy type 1 also have disrupted dream sleep, which can manifest as acting out dreams (e.g., a syndrome known as REM sleep behavior disorder) and periodic leg movements in sleep.
What causes narcolepsy type 1? It is a disorder of the nervous system in which there is immune system mediated destruction of brain cells that contain hypocretins (aka orexins). These brain cells are located in a brain region called the hypothalamus, and they are critical to maintenance of wakefulness, continuity of sleep, and coordination of the timing and features of dream sleep (i.e., REM sleep).
Diagnosing Narcolepsy: Cataplexy is a symptom that occurs almost exclusively in people with narcolepsy type 1, so its presence strongly suggests this diagnosis. However, cataplexy can sometimes be subtle or mild, making additional testing necessary. As in idiopathic hypersomnia, diagnosis depends on ruling out causes of secondary hypersomnia and performing a polysomnogram (overnight sleep test) with multiple sleep latency test (MSLT). On the MSLT, it takes less than 8 minutes on average for people with narcolepsy type 1 to fall asleep, and dream sleep (REM) is observed on at least two naps. People with narcolepsy type 2 show the same results on MSLT as those with cataplexy. In cases with persistent diagnostic uncertainty (e.g., because cataplexy is subtle or not clearly present, which can especially be the case in African Americans, who may also present differently in other ways), testing for hypocretin within cerebrospinal fluid (CSF, by lumbar puncture) can be valuable. People with narcolepsy type 1 will demonstrate low or undetectable hypocretin levels. In the U.S., CSF can be sent to Mayo Clinic Laboratories for hypocretin/orexin testing. Follow these links for an overview of CSF orexin/hypocretin testing procedures and detailed test instructions.
The symptoms of narcolepsy often begin in adolescence. These symptoms may also present differently in adolescents and can be challenging to recognize. Younger children in particular may be unable to articulate what they are experiencing. For more information, this article provides an overview of the differences between adolescents and adults with narcolepsy and cataplexy. The narcolepsylink.com website also contains information on recognizing the symptoms of narcolepsy in children.
About Kleine-Levin Syndrome
Kleine-Levin syndrome (KLS) is a rare disorder in which affected people experience episodes at least once per year during which they sleep for excessively long durations (often 16-20 hours/day) for days or weeks at a time. During these episodes, they will have abnormal perception or cognition, changes in eating, or disinhibition (e.g., acting inappropriately sexual). Between episodes, their alertness, behavior, and thinking are normal.
Both the International Classification of Sleep Disorders (ICSD) and the Diagnostic and Statistical Manual of Mental Disorders (DSM) include criteria to diagnose KLS, but there are no biomarkers—no substances in the body that can be measured—that can help doctors in making the diagnosis of KLS. Some scientists who study KLS think that it is caused by something in the immune system that causes dysfunction in the part of the brain called the hypothalamus. Other researchers have shown abnormal functioning in the nearby brain region called the thalamus on special imaging studies.
About Hypersomnia Associated With Certain Disorders
In patients with certain other disorders, excessive daytime sleepiness and/or long sleep times are commonly present and can be very similar to that seen in idiopathic hypersomnia. As with IH, hypersomnolence associated with these other conditions can cause substantial impairment and worsening of quality of life. However, hypersomnia associated with these other disorders is distinguished from IH because the sleepiness is thought to be directly caused by the primary disorder or is strongly associated with the other disorder, even though the cause is not known. For example, Parkinson’s disease and myotonic dystrophy commonly present with hypersomnolence. Other rare disorders known to have associated hypersomnolence include Ehlers-Danlos syndrome, POTS (postural tachycardia syndrome), and Prader-Willi syndrome.