Narcolepsy is a chronic neurological sleep disorder characterized by excessive daytime sleepiness. In people with narcolepsy, the brain doesn’t adequately regulate sleep and wake cycles, leading to abnormal sleep patterns.
A standard sleep cycle includes two types of sleep: rapid eye movement (REM) sleep and non-REM (NREM) sleep. During REM sleep, people dream and their bodies are limp. Normally it takes a person an hour to an hour-and-a-half to enter REM sleep. People with narcolepsy can enter REM sleep in just 15 minutes.
For people without narcolepsy, REM sleep, NREM sleep, and wakefulness are separate states. However, in people with narcolepsy the states of being asleep and being awake blur together. For example, the muscle limpness that normally only occurs during REM sleep can occur suddenly when a person is awake.
Narcolepsy is a rare condition — an estimated 135,000 to 200,000 Americans have narcolepsy. Symptoms of narcolepsy can appear at any age, but usually manifest before age 50. Some researchers have identified peak times for development of narcolepsy around ages 15 and 36. Narcolepsy impacts men and women equally.
There are two main types of narcolepsy — type 1, or narcolepsy with cataplexy, and type 2, or narcolepsy without cataplexy. The terminology used to describe types of narcolepsy changed in 2014 with the publication of the third edition of The International Classification of Sleep Disorders. Rarely, people can develop secondary narcolepsy as the result of an injury.
Common symptoms of type 1 narcolepsy include:
The presence of cataplexy is the primary differentiator between type 1 and type 2 narcolepsy. Cataplexy, the sudden loss of muscle tone, is usually triggered by strong emotions like anger, stress, or excitement. Cataplexy episodes range in severity. A person may experience a momentary drooping of their eyelids or a complete inability to move or speak. People with type 1 narcolepsy may rarely have cataplexy episodes or have multiple episodes each day.
Learn more about cataplexy in Symptoms of Narcolepsy.
Low levels of a brain chemical called hypocretin (sometimes called orexin) contribute to the development of type 1 narcolepsy. Hypocretin helps the body regulate sleep. Approximately 90 percent of people with type 1 narcolepsy have low or undetectable hypocretin levels.
Low levels of hypocretin may be related to an autoimmune process, where the body’s immune system mistakenly attacks the nerve cells in the brain that produce hypocretin. Genetic factors are also involved in type 1 narcolepsy.
Learn more about the causes of narcolepsy.
Diagnosing narcolepsy of any type can be challenging, and many people experience several years’ delay between the onset of symptoms and a diagnosis. The diagnostic process involves differential diagnosis — ruling out other health conditions that may cause similar symptoms. A health care provider may consider the possibility of other sleep disorders like idiopathic hypersomnia (excessive sleepiness), insufficient sleep syndrome (chronic sleep deprivation), or obstructive sleep apnea (disordered breathing during sleep). A provider will also consider the possibility of other health or psychiatric conditions or substance use that could impact sleep patterns.
To receive an official diagnosis of type 1 narcolepsy, a person must exhibit excessive daytime sleepiness for at least three months that cannot be explained by another health condition or medication/substance use. They must also have one of two additional sets of criteria:
Learn more about the diagnosis of narcolepsy.
Type 2 narcolepsy is also referred to as narcolepsy without cataplexy. Type 2 narcolepsy is rare and there is limited information on its prevalence. One estimate suggests that type 2 narcolepsy accounts for 36 percent of people with narcolepsy.
The symptoms of type 2 narcolepsy are similar to those of type 1. People with type 2 can experience excessive daytime sleepiness, sleep attacks, sleep paralysis, disrupted nighttime sleep, and hallucinations. What sets them apart is the lack of cataplexy. However, in some cases, people with type 2 develop cataplexy and thus transition to type 1.
The precise reason why people develop type 2 narcolepsy remains unknown. Unlike type 1 narcolepsy, hypocretin levels in people with type 2 tend to be normal. Between 10 percent and 24 percent of those with type 2 narcolepsy have low hypocretin levels, compared to 90 percent of those with type 1.
Individuals with type 2 who also have lower hypocretin levels may go on to develop cataplexy, and their condition may be reclassified. A study of 171 people with type 2 narcolepsy found that 33 percent of those with low hypocretin levels developed cataplexy an average of 15 years after the onset of daytime sleepiness.
Diagnosing narcolepsy without cataplexy also relies heavily on the process of differential diagnosis. A health care provider may consider the possibility of other sleep disorders — including idiopathic hypersomnia, insufficient sleep syndrome, or problems related to working nights — when diagnosing type 2 narcolepsy.
To be officially diagnosed with type 2, a person must have experienced three months of excessive daytime sleepiness that cannot be explained by another condition or medication. They must also have a positive MSLT sleep study.
Secondary narcolepsy (also called symptomatic narcolepsy) can be caused by an injury to the hypothalamus, the region at the base of the brain that controls several functions, including sleep. Stroke, head trauma, tumors, or inflammatory diseases impacting the nervous system can injure the hypothalamus.
People with secondary narcolepsy share many of the same symptoms as those with types 1 and 2. One of the most clear differentiating factors between secondary narcolepsy and the other types of narcolepsy is sleeping 10 or more hours a day.
People with secondary narcolepsy may also exhibit signs of neurological damage, including:
Diagnosing secondary narcolepsy may require an MRI to confirm damage to the hypothalamus.
The focus of treatment for all types of narcolepsy is managing symptoms. Treatment will depend on your narcolepsy type, particularly whether or not you experience cataplexy. The following lifestyle measures and treatment options may help people with narcolepsy manage symptoms and improve quality of life:
Learn more about narcolepsy treatments.