Narcolepsy Testing and Diagnosis

Narcolepsy has been poorly portrayed in popular culture. It does not cause abrupt sleeping at comically inopportune moments. It is an uncommon neurological disorder affecting up to 200,000 people in the U.S.

People with narcolepsy report excessive daytime sleepiness despite adequate sleep at night. They may also experience hallucinations, sleep paralysis, and cataplexy. Cataplexy is sudden muscle weakness while awake.

Narcolepsy can be hard to diagnose, with symptoms that are similar to other, more common, conditions. 

Primary Care Evaluation

A visit with a primary care doctor is the first step in diagnosing narcolepsy. They help rule out medications, depression, and other medical conditions that may be causing the symptoms. A medical history review can reveal conditions that may mimic narcolepsy, including traumatic brain injury.

The primary care doctor may also rule out other sleep disorders that can disrupt the sleep-wake cycle. Sleep apnea, insomnia, restless leg, and chronic snoring are all common.

Once other causes are ruled out, the patient is referred to a sleep specialist with experience diagnosing narcolepsy. As described by Healthline, sleep physicians generally perform two diagnostic tests for this disorder. 

Polysomnogram

A polysomnogram is a sleep study during which the patient spends their regular sleeping hours in a lab. The study usually takes place at night. Sleep labs can be in hospitals or clinics. 

Electrodes are placed on the outer eyelids, chin, and scalp for the test. They measure signals indicating sleep, wakefulness, and REM sleep. The patient is observed by a technician and has monitors measuring respiration and heart rate.

The purpose of a polysomnogram for diagnosing narcolepsy is to look for sudden waking and rapid entry into REM sleep. It also measures sleep efficiency. Sleep efficiency is the percent of sleep hours actually spent sleeping. Normally this number is around 85%.

This test is also used to evaluate other common sleep disorders including sleep apnea and excessive snoring.

Multiple Sleep Latency Test (MSLT)

A Multiple Sleep Latency Test (MSLT) takes place during the day. Patients are allowed to nap every two hours for a total of 4-5 nap opportunities during the study.

If the patient falls asleep the nap is interrupted after 15 minutes. If they do not fall asleep, the session ends after 20 minutes.

Electrodes provide information about how long it takes the patient to fall asleep and how soon they enter REM sleep. Those with narcolepsy often fall asleep quickly and enter REM sleep at least twice during the test.

Additional Testing, Diagnosis, Treatment

A lumbar puncture may be used to detect low levels of the neurotransmitter hypocretin. 

Narcolepsy diagnoses are categorized into two types. Type 1 is narcolepsy with cataplexy or low hypocretin. Type 2 does not have cataplexy or low hypocretin.

Depending on the type of narcolepsy and the severity of symptoms, treatment may include lifestyle, dietary, and sleep schedule changes. A sleep physician may also prescribe medication. Wake-promoting medicines that differ from traditional stimulants are used. Antidepressant drugs may be an option for some patients. Sodium oxybate reduces muscle weakness and daytime sleepiness.

 

Sources:

https://www.healthline.com/health/narcolepsy/narcolepsy-test#whats-next

https://www.workplacetesting.com/definition/2673/sleep-efficiency-se

https://www.sleepfoundation.org/physical-health/cataplexy

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