FAQs: Narcolepsy & Hypersomnia Research

What is Narcolepsy Type 1, also called Narcolepsy with Cataplexy?

The main symptoms of narcolepsy type 1 (NT1) are excessive daytime sleepiness, cataplexy, sleep paralysis, hypnagogic hallucinations, and disturbed nocturnal sleep.  It affects about 0.03% of the population (1 for 3,000 individuals) in most countries in the world.  About half of all patients start narcolepsy before age 18, in rare cases as young as 3 years old, and in general the younger it starts, the more severe and abruptly the disease strikes; in young children one often observed a regression where tantrums and bad behavior restarts because the child is always exhausted. A rapid gain of weight often also occurs.

What is Narcolepsy Type 2, also called Narcolepsy without Cataplexy?

Many patients do not have all the symptoms of narcolepsy, for example, they can be tired and need to take multiple naps without having cataplexy. Some need 12 hours of sleep every day and still feel exhausted. Other are plagued by vivid dreams and sleep paralysis but never experienced cataplexy. Typically, in these cases, an MSLT is done and if the pattern looks like NT1 (mean sleep latency ≤ 8 min; ≥ 2 SOREMPs in 5 naps), the patient is called type 2 narcolepsy (NT2, or narcolepsy without cataplexy). If the MSLT shows sleepiness with a short mean sleep latency (≤ 8 minutes) but does not show REM sleep in more than 1 nap, or reports sleeping every day more than 10 hours while still feeling tired, the patient is diagnosed as Idiopathic Hypersomnia.

What is Idiopathic Hypersomnia?

These conditions are called “hypersomnia disorders”. Patients with these conditions are sleepy during the day for no reason, and/or need a lot of sleep and are always tired. To be diagnosed with a hypersomnia disorder, one must have excluded other causes of sleepiness due to poor sleep like sleep apnea, sleep deprivation, or circadian disorder abnormalities; meaning when the timing of sleep within the 24 hr day is abnormal. NT1 is caused by a lack of a chemical called hypocretin or orexin; these patients have REM sleep abnormalities and almost always have cataplexy. NT2 patients do not have cataplexy, and generally resemble patients with NT1, notably with respect to their diagnostic MSLT test result. Idiopathic Hypersomnia patients are like NT2, but do not have REM symptoms or a narcolepsy like MSLT with REM sleep onsets.

What is an MSLT?

The Multiple sleep Latency test (MSLT) is the gold standard diagnostic test for narcolepsy and hypersomnia.  The polysomnogram is an overnight test, which takes continuous measurements of the EEG, EOG, EMG, ECG, breathing and leg movements.  It is mostly used to exclude obstructive sleep apnea, a common differential diagnosis, but may also reveals abnormalities in REM sleep, such as a very short REM sleep latency in NT1 in 50% of the time.

The MSLT, conducted after a PSG, measures the time taken by patients to fall asleep (sleep latency) during naps in a quiet environment and the occurrence of REM sleep in these naps. In narcolepsy or hypersomnia, patients fall asleep much more rapidly than controls, with a mean sleep latency of less than 8 minutes considered revealing of pathological sleepiness.   Most specific for the diagnosis however is the fact patients with narcolepsy enter into REM sleep frequently in these naps, with at least two REM sleep events observed in 5 naps considered diagnostic for narcolepsy, whether NT1 (with cataplexy or hypocretin deficiency) or narcolepsy type 2 (NT2 without cataplexy or hypocretin deficiency).  Recent results have shown that the MSLT is only repeatable in NT1, yet it is still used as the main diagnostic tool.