What Is the Difference Between Narcolepsy Type 2 and Idiopathic Hypersomnia?

If you have excessive daytime sleepiness that interferes with how you function, you may wonder if you might have narcolepsy. The sleep disorder occurs equally in men and women and affects about 1 out of every 2,000 people. It is estimated that more than half of the people who have narcolepsy do not know it. In fact, it often can go undiagnosed for 10 years or more.1,2

Narcolepsy type 1

Narcolepsy type 1 (NT1) is different from narcolepsy type 2 (NT2), and both differ from a sleep disorder called idiopathic hypersomnia. NT1 occurs with low levels of a brain hormone called hypocretin or with a condition called cataplexy. This is a form of muscle paralysis that occurs while the person with narcolepsy is awake. It causes a sudden loss of muscle tone that results in a slack jaw or weakness in the arms, legs, or trunk.2

Narcolepsy type 2 and idiopathic hypersomnia

However, in NT2 and idiopathic hypersomnia, there is no cataplexy. People who have idiopathic hypersomnia find themselves sleepy during the day even after a full night of sleep. They also can have trouble waking up and may feel lightheaded when they stand up quickly. They may find that even after taking a long nap, they wake up feeling unrefreshed.3,4

REM sleep differences

When people without a sleep disorder fall asleep, they enter rapid eye movement (REM) sleep after around 60 to 90 minutes. This is when a person dreams and the brain keeps muscles limp during this stage of sleep. It is a natural way to prevent a person from acting out their dreams. However, in a person with narcolepsy, REM sleep starts much quicker, often within 15 minutes of falling asleep.4,5

When this happens, it is called a SOREMP, or a sleep-onset REM period that happens within 15 minutes of falling asleep. If you are having SOREMPs, you are having REM sleep early in your sleep cycle. This can be a sign of NT2 but not of idiopathic hypersomnia.4,5

Tests to identify SOREMPs

This is not something you would be able to find out on your own. To learn whether you are having SOREMPs, your doctor may recommend testing at a sleep clinic. There, you will have a multiple sleep latency test (MSLT), which will check your daytime sleepiness by seeing how quickly you fall asleep.

The test can also determine when you enter REM sleep. You might also be given a polysomnogram (PSG). During this, your doctor looks at the number of SOREMPs you have as you sleep. Having 2 or more SOREMPs is what makes NT2 different from idiopathic hypersomnia.4,5

Why sleep tests can be inconclusive

Diagnosing NT2 versus idiopathic hypersomnia is not an exact science. Sleep doctors are finding that some people may have normal results the first time around but abnormal results when the test is repeated. In other words, the number of SOREMPs is not stable in many people.

This means the test may be unreliable, and it may not always be clear if the person has idiopathic hypersomnia or NT2. Also, researchers are finding that nearly 20 percent of people with NT2 sleep continuously for long periods, like for 11 out of 24 hours. This amount of sleep meets the criteria for a diagnosis of idiopathic hypersomnia.3

The future of NT2 and idiopathic hypersomnia diagnoses

Now, sleep researchers are looking for more reliable ways to decide whether someone has idiopathic hypersomnia or NT2. There is even talk about combining IH and NT2 into a single diagnosis.6

NT2 and idiopathic hypersomnia (without a long sleep time) may be put into one category called “narcolepsy spectrum disorder.” Idiopathic hypersomnia (when it has a long sleep time) and NT1 would remain 2 distinct disorders.6

Diagnosing your sleep disorder can definitely get confusing. However, the good news is that whether you are diagnosed with idiopathic hypersomnia or NT2, there are medicines to improve the quality of your sleep and help you feel less sleepy during the day.7

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