What Is the Difference Between Narcolepsy Type 1 and Type 2?

Cataplexy and Hypocretin Testing Can Differentiate the Sub-Types

A woman collapses to the floor due to cataplexy in narcolepsy type 1
A woman collapses to the floor due to cataplexy in narcolepsy type 1. Science Photo Library/Getty Images

Narcolepsy is always characterized by excessive daytime sleepiness, but there are other symptoms and test results that are used to differentiate the sub-types of the condition. There are two types of narcolepsy, but what is the difference between narcolepsy type 1 and type 2? Learn about these differences, including the role of cataplexy and testing for hypocretin levels in the cerebrospinal fluid (CSF).

Symptoms of Narcolepsy May Differentiate Sub-Types

Both types of narcolepsy include an irrepressible need to sleep or daytime lapses into sleep. Without sleepiness, narcolepsy is not the proper diagnosis. There are some other associated symptoms, and some of these can help to differentiate the sub-types.

There are two types of narcolepsy: type 1 and type 2. Type 1 may include the presence of the symptom of cataplexy. Cataplexy is defined as more than one episode of brief, usually symmetrical sudden loss of muscle tone with retained consciousness. This weakness may be provoked by strong emotions. These emotions are usually positive; for example, cataplexy may be associated with laughter. The weakness may involve the face, arms, or legs. Some narcoleptics will have droopy eyelids, mouth opening, tongue protrusion, or head bobbing. Some people can collapse to the ground during an attack of cataplexy.

Both types of narcolepsy may also include sleep paralysis and hypnagogic hallucinations. Fragmented sleep at night often occurs in both conditions as well.

The Role of Testing for Hypocretin and the MSLT

Specific testing can also be used to differentiate between the two sub-types of narcolepsy. Excessive daytime sleepiness is determined based on the results of a multiple sleep latency test (MSLT).

This test follows a standard sleep study and includes four or five nap opportunities that occur at 2-hour intervals. The subject is given an opportunity to sleep, and people with narcolepsy will fall asleep in less than 8 minutes on average. In addition, REM sleep will occur within 15 minutes of sleep onset in at least two of the nap opportunities.

Moreover, testing of the hypocretin levels in the CSF fluid as part of a lumbar puncture can be revealing. If the levels are measured to be less than 110 pg/mL, this is consistent with a diagnosis of type 1 narcolepsy. If the levels are normal (or not measured) and cataplexy is not present, type 2 narcolepsy is diagnosed if the MSLT is positive. If the hypocretin level is measured to be abnormal later, or if cataplexy subsequently develops, the diagnosis can be changed to type 1.

Though narcolepsy is a rare condition, it occurs commonly enough, with type 1 affecting about 1 in 5,000 people. The diagnosis should be made by a sleep specialist who is able to apply the proper testing and subsequently provide effective treatment.

If you are concerned that you may have symptoms of narcolepsy, seek further evaluation by a sleep expert who can provide you the care and support that you need.

Source:

American Academy of Sleep Medicine. International classification of sleep disorders, 3rd ed. Darien, IL: American Academy of Sleep Medicine, 2014.

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