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Narcolepsy (cont.)

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How is narcolepsy diagnosed?

The diagnosis of narcolepsy is based on a clinical evaluation, specific questionnaires, sleep logs or diaries, and the results of sleep laboratory tests.

Clinical evaluation

Clinical evaluation includes a detailed medical history and physical examination by a physician.


Questionnaires may be used in the assessment of patients with symptoms that suggest narcolepsy. The Stanford Narcolepsy Questionnaire is an extensive questionnaire that can provide the physician with valuable information on all symptoms of narcolepsy, but especially on cataplexy. The Epworth Sleepiness Scale is a brief self-administered questionnaire that provides an estimate of the degree of daytime sleepiness. A person rates the likelihood of falling asleep during specific activities. Using the scale from 0 to 3 below, the person ranks their risk of dozing in the chart below.

0 = Unlikely to fall asleep
1 = Slight risk of falling asleep
2 = Moderate risk of falling asleep
3 = High likelihood of falling asleep

SituationRisk of Dozing
Sitting and reading
Watching television
Sitting inactive in a public place
As a passenger in a car riding for an hour, no breaks
Lying down to rest in the afternoon
Sitting and talking with someone
Sitting quietly after lunch, without alcohol
In a car, while stopped for a few minutes in traffic

After ranking each category, the total score is calculated. The range is 0 to 24, with the higher the score the more sleepiness.


  • 0 to 9 = Average daytime sleepiness
  • 10 to 15 = Excessive daytime sleepiness
  • 16 to 24 = Moderate to severe daytime sleepiness

Sleep logs or sleep diaries

Sleep logs or sleep diaries for 2 to 3 weeks are recommended in the evaluation of any patient with excessive daytime sleepiness. Sleep diaries record the patient's usual sleep patterns (sleep deprivation, irregular sleep/wake pattern, interrupted sleep), alcohol and/or drug use, and common behaviors that cause the patient to lose sleep (for example, Internet syndrome - surfing the Internet until late at night, causing sleep deprivation and daytime sleepiness.) This information may be helpful in the evaluation of a patient with excessive daytime sleepiness.

Sleep laboratory tests

Sleep laboratory tests ("sleep studies") for narcolepsy include polysomnography (PSG) and the multiple sleep latency test (MSLT). Polysomnography (PSG) is a full night recording of several different physiological factors of a patient's sleep. A PSG is necessary to insure good quality sleep to identify any untreated causes for daytime sleepiness such as obstructive sleep apnea (OSA). The PSG is followed the next day by the multiple sleep latency test (MSLT), which is a recording of the patient's tendency to fall asleep during the day. These procedures provide objective measures of daytime sleepiness and REM sleep abnormalities.

Daytime sleepiness is measured in the MSLT by the sleep latency (SL) time. This is the time from the beginning of the recording to the onset of sleep. In healthy individuals, the SL time is more than 10 minutes, whereas in narcolepsy, it could be as short as 0.5 minutes (an almost immediate onset of sleep).

REM sleep

REM sleep is named for the rapid eye movements (REM) that characterize this phase of sleep. In REM sleep dreams are vivid, muscle activity is suppressed, and brain activity is high. The REM sleep abnormality that is characteristic of narcolepsy is referred to as sleep onset REM periods. In healthy individuals, the first REM sleep period occurs about 80 to 120 minutes after the onset of sleep. By contrast, in narcolepsy, the initial REM sleep period usually occurs within 15 minutes of the onset of sleep. In addition, narcolepsy patients will have two or more sleep onset REM periods during the multiple sleep latency test (MSLT) in the daytime.

PSG is also helpful in excluding other causes of daytime sleepiness, such as sleep apnea syndrome (SAS), periodic limb movements in sleep (PLMS), and sleep disruptions. In some cases, repeat tests may be recommended if there is worsening of the symptoms of narcolepsy despite treatment or if an additional sleep disorder is suspected (for example, sleep apnea syndrome).

Maintenance of wakefulness test (MWT)

Maintenance of wakefulness test (MWT) may be used to evaluate the effects of the treatment for narcolepsy. This test is a recording that measures the ability of a subject to stay awake during the day.

The diagnostic criteria for narcolepsy are described in the International Classification of Sleep Disorders. These criteria indicate that the diagnosis may be based on clinical symptoms alone if both excessive daytime sleepiness and cataplexy are present. If cataplexy is not present, however, the diagnosis should be based on the clinical symptoms and polysomnographic findings.

The blood test for a type of HLA

The blood test for a type of HLA (Human Leukocyte Antigen) has been observed to have a very high association with narcolepsy. Certain types of HLA are part of an individual's genetic or hereditary makeup and can be characteristic of certain conditions, especially autoimmune diseases. The particular HLA type associated with narcolepsy is not unique for this condition as it is also found in 20% of the general population. Therefore, HLA typing is used for the diagnosis of narcolepsy. However, there is a strong association with certain genes in patients diagnosed with narcolepsy and cataplexy. Many patients are known to have a specific HLA gene variant called DQB1*0602. Scientists continue to work in this area to better understand the pathogenesis of narcolepsy.

Medically Reviewed by a Doctor on 10/6/2016


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