Gina Johnson
Narcolepsy is a sleep disorder that affects an estimated 25 to 50 people out of every 100,000 worldwide. Due to its rarity and the fact that its symptoms can be similar to those of other conditions, it can be challenging to diagnose. Typically, a medical doctor or primary care physician (PCP) coordinates the diagnostic process, which involves a review of symptoms, medical history, and a basic physical exam. If narcolepsy is suspected, a referral is made to a sleep specialist, neurologist, or psychiatrist, who may recommend a sleep study or polysomnogram (PSG) to track brain activity and identify any sleep disorders. While a PSG is a common diagnostic tool, it is not the only method, and other tests such as blood tests, brain scans, and questionnaires can also aid in diagnosing narcolepsy.
| Characteristics | Values |
|---|---|
| Diagnosis by a health professional | Required |
| Tests | Polysomnography (PSG), Multiple Sleep Latency Test (MSLT), Maintenance of Wakefulness Test, Spinal Tap (Lumbar Puncture), Blood Test, Brain Scan, Human Leukocyte Antigen (HLA) Testing |
| Symptoms | Excessive daytime sleepiness, sleep attacks, sudden outbursts, cataplexy |
| Sleep Patterns | Falling asleep in less than eight minutes, entering REM sleep quickly |
| Sleep Study Preparation | Stabilizing sleep schedule, no medications or substances that interfere with sleep, sleep diary |
| Other Factors | Age, gender, medical history, family history, physical exam |
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What You'll Learn
Polysomnography (PSG)
During a PSG, data is collected from 7 channels: EEG (usually 4 channels), EOG (2), and chin EMG (1). This information is then scored in 30-second epochs as "awake" or one of the 4 sleep stages: 1, 2, 3, and REM (Rapid Eye Movement) sleep. Stages 1-3 are collectively referred to as non-REM sleep, with stage 3 being "slow-wave" or "deep sleep" due to its relatively wide brain waves. Stages 1 and 2 are considered "light sleep". The percentage of time spent in each sleep stage varies by age, with older individuals experiencing decreasing amounts of REM and deep sleep.
In the context of narcolepsy diagnosis, PSG plays a crucial role in tracking breathing, eye movement, muscle movement, and brain activity. People with narcolepsy tend to enter REM sleep much faster than those without the condition, and their sleep is often interrupted by periods of wakefulness. PSG can capture these distinct characteristics, aiding in the diagnosis of narcolepsy. Additionally, PSG can help rule out other sleep disorders, such as sleep apnea, which shares similar symptoms with narcolepsy, including excessive daytime sleepiness.
PSG is typically followed by the Multiple Sleep Latency Test (MSLT), which is conducted in the morning immediately afterward. During the MSLT, the patient remains connected to the sensors used in the PSG and is instructed to try to fall asleep at five separate intervals. The MSLT measures how quickly the patient falls asleep and enters REM sleep, providing additional data for the diagnosis of narcolepsy.
While PSG is an essential tool in the diagnosis of narcolepsy, it is just one component of a comprehensive evaluation. Other tests, such as HLA testing and the measurement of hypocretin levels, are also considered in conjunction with PSG results to establish a definitive diagnosis of narcolepsy.
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Multiple Sleep Latency Test (MSLT)
The Multiple Sleep Latency Test (MSLT) is a full-day test that checks for excessive daytime sleepiness by measuring how quickly you fall asleep in a quiet environment during the day. It is also known as a daytime nap study and is used to diagnose narcolepsy and idiopathic hypersomnia.
The MSLT is typically conducted in the morning, following an overnight sleep study, such as a polysomnogram (PSG). During the test, you will be given four to five opportunities to sleep every two hours during normal wake times. You will lie quietly in bed and try to fall asleep, and once you do, you will be awakened after 15 minutes. If you are unable to fall asleep within 20 minutes, the nap trial will end, and you will have a break until the next nap trial begins.
The test measures how long it takes for you to fall asleep and how quickly you enter rapid eye movement (REM) sleep. People with narcolepsy tend to fall asleep in less than eight minutes on average and enter REM sleep much earlier than those without the condition. A positive MSLT for narcolepsy is obtained when the patient falls asleep with a mean sleep latency below eight minutes and enters REM sleep in at least two of the naps.
It is important to prepare for the MSLT correctly to ensure valid results. This includes stabilizing your sleep schedule for at least a week beforehand and discontinuing any medications or substances that could interfere with your sleep during the test.
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Human leukocyte antigen (HLA) testing
HLA-DQB1*06:02 is strongly associated with narcolepsy, and its presence can increase the risk of developing the condition. In 2009, several epidemiological studies showed an increased incidence of NT1 after the H1N1 vaccination in individuals carrying the HLA-DQB1*06:02 allele. The H1N1 viral peptides are presented by the HLA-DQB1*06:02 molecules to CD4 T lymphocytes by antigen-presenting cells. The activated CD4 and CD8 cells then recognise the H1N1 viral peptide and infiltrate the hypothalamus, where the destruction of hypocretin neurons is mediated by inflammatory cytokines. This process has helped reveal the link between HLA and disease development.
HLA-DQB1*06:02 is also associated with narcolepsy type 2 (NT2), although its absence does not rule out NT2. A meta-analysis of four major ethnic groups (Asians, Afro-Americans, Amerindians, and Caucasians) found that HLA-DQB1 typing was useful in the diagnosis of narcolepsy with cataplexy. Cataplexy is a sudden and temporary loss of muscle tone that commonly occurs with positive emotions. It is an important differentiating factor between NT1 and NT2, as it only occurs in NT1.
In summary, while HLA testing alone cannot diagnose narcolepsy, it can be a valuable tool when combined with other information such as symptoms, physical exams, and results from sleep studies and other tests. A doctor can consider all of this information together to determine whether a patient meets the established criteria for narcolepsy.
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Epworth Sleepiness Scale
The Epworth Sleepiness Scale (ESS) is a self-administered questionnaire designed to assess an individual's "daytime sleepiness". Developed by Dr Johns in 1990, the ESS comprises eight questions, each with a 4-point rating scale (ranging from 0 to 3). Respondents are asked to rate their likelihood of dozing off or falling asleep while engaged in eight different activities. These activities vary in their sleep-inducing potential. The ESS score, obtained by summing the scores of the eight items, can range from 0 to 24. Higher scores indicate a greater propensity for daytime sleep.
The ESS is a quick assessment, taking no more than 2-3 minutes to complete. It does not consider an individual's subjective feelings of alertness or drowsiness at a particular time. Instead, it provides an estimate of a person's average sleep propensity across a range of daily activities.
The ESS has been modified over the years, with changes made in 1997 to encourage respondents to answer all the questions. This self-reporting measure is also used in clinical settings, where clinicians may compare ESS scores before and after specific treatments for sleep disorders.
The ESS is a valuable tool in the context of diagnosing sleep disorders like narcolepsy. Narcolepsy is a rare condition that often takes years to diagnose. It is characterised by excessive daytime sleepiness, sudden sleep attacks, and the tendency to enter REM sleep unusually quickly. While a sleep study is a key diagnostic tool, the ESS can provide additional insights into an individual's sleep patterns and propensity for daytime sleepiness, contributing to a comprehensive understanding of their sleep health.
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Lumbar puncture
While a sleep study is a common method for diagnosing narcolepsy, a lumbar puncture, also known as a spinal tap, can also be used. This procedure is typically carried out by neurologists to rule out neurological issues such as brain infections or multiple sclerosis.
During a lumbar puncture, a small amount of cerebrospinal fluid (CSF) is extracted. In the context of narcolepsy, this fluid is tested for hypocretin or orexin levels. Narcolepsy Type 1 (NT1) is characterised by a deficiency of this chemical, which results in REM sleep abnormalities and cataplexy.
To diagnose NT1, the CSF is analysed for the presence of hypocretin. If undetectable levels are found and no other neurological issues are present, a diagnosis of narcolepsy can be made. This test is considered the most definitive for NT1.
It is important to note that a lumbar puncture is typically not the first-line test for narcolepsy. Sleep studies, such as polysomnography and the Multiple Sleep Latency Test (MSLT), are often conducted first to observe sleep patterns and rule out other conditions. However, in cases where there is a strong suspicion of NT1, or when other tests are inconclusive, a lumbar puncture can provide a more definitive diagnosis.
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Frequently asked questions
Narcolepsy is a rare condition that affects 25 to 50 people out of every 100,000 worldwide. People with narcolepsy experience excessive daytime sleepiness (EDS) and may fall asleep during the day. It can be difficult to diagnose because the symptoms can be similar to those of other conditions.
There are several tests that can be used to diagnose narcolepsy, including sleep studies (polysomnogram or PSG), Multiple Sleep Latency Tests (MSLT), Maintenance of Wakefulness Tests, blood tests, brain scans, and spinal taps (lumbar puncture). Sleep studies are often conducted overnight in a sleep clinic, and they track your breathing, eye movement, muscle movement, and brain activity. The MSLT is usually conducted the morning after the PSG and measures how quickly you fall asleep and enter REM sleep.
While sleep studies are a common tool for diagnosing narcolepsy, they are not the only method. Other tests such as blood tests, brain scans, and spinal taps can also be used to diagnose narcolepsy. Additionally, questionnaires such as the Epworth Sleepiness Scale can be used to measure excessive daytime sleepiness. However, a combination of tests and evaluations is typically used to diagnose narcolepsy accurately.
