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), testing for hypocretin within cerebrospinal fluid (by lumbar puncture) can be valuable. People with narcolepsy type 1 will demonstrate low or undetectable hypocretin levels.
Revised 9/2017 by Lynn Marie Trotti, MD, MSc, Chairperson, HF Medical Advisory Board