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Beside excessive daytime sleepiness, patients may display the following symptoms:
Cataplexy – a sudden weakening of the muscles, often triggered by a strong emotion. While cataplexy can manifest as something as minor as a slight slackening of the facial muscles, in extreme cases, a person may experience total collapse or even muscle paralysis. Cataplexy is a cardinal symptom as it almost always indicates that the cause of the narcolepsy is a lack of hypocretin in the brain.
Sleep paralysis - the temporary inability to talk or move when waking; it may last a few seconds to minutes.
Hypnagogic hallucinations – vivid, sometimes disturbing dreamlike experiences that occur while dozing, falling asleep and/or upon awakening.
Automatic behavior – a person continues to function or talk while being half asleep, and awakens with no memory of doing these activities.
Difficulties maintaining sleep – Nighttime sleep is disturbed. Patients often do fall asleep rapidly but are unable to stay asleep for more than a few hours at a time. Nighttime eating and excessive dreaming with motor activity (acting out dreams, see also REM sleep Behavior Disorder) also frequently occur.
Obesity – Many patients with narcolepsy also gain weight as the result of inactivity and sleepiness.
The cause of narcolepsy with and without cataplexy
In most cases of narcolepsy with cataplexy (and in rare cases without cataplexy), all the symptoms are caused by the loss of approximately 70,000 brain cells producing a chemical called hypocretin, a finding made at Stanford University. Visit the Center for Narcolepsy for more details.
In most cases of narcolepsy without cataplexy (and in rare cases with cataplexy), the cause of the symptoms is unclear and the diagnostic is purely based on the result of an abnormal sleep test called the multiple sleep latency test (MSLT).
If all the common symptoms of narcolepsy are present, diagnosing the disorder is fairly straightforward. However, if sleep attacks are isolated and there is only mild or no cataplexy, making a correct diagnosis is more challenging. It requires excluding carefully insufficient sleep (sleep deprivation), disturbed nocturnal sleep, insomnia, circadian rhythm disorders, sleep-related breathing (sleep apnea) disorders and psychiatric disorders. A general medical check up excluding anemia, hypothyroidism, heart or other general medical issues is essential.
Stanford Sleep Specialists use two main tests to diagnose narcolepsy: the nocturnal polysomnogram and the multiple sleep latency test (MSLT). The polysomnogram continuously records brain waves during sleep, as well as a number of nerve and muscle functions during nighttime sleep. During the test, the narcoleptic will usually fall asleep rapidly, enter REM sleep quickly, and potentially awaken frequently during the night.
For the MSLT, a person is given 4-5 opportunities to sleep every two hours during normal wake times. The specialist uses the test to measure the extent of daytime sleepiness (how fast the patient falls asleep in each nap, also called sleep latency), and also how quickly REM sleep begins, since narcoleptics fall asleep quickly and experience REM sleep early. A positive MSLT (diagnostic for narcolepsy) is obtained when the patient did fall asleep with a mean sleep latency below 8 minutes in the naps, and had at least 2 naps where REM sleep was reached.
In addition to the above, Stanford Sleep Specialists will commonly performed a blood genetic test for narcolepsy if they suspect hypocretin deficiency called Human Leukocyte Antigen (HLA) DQB1*06:02 typing. Almost 99% of subjects where narcolepsy is caused by a lack of hypocretin are DQB1*06:02 positive, but approximately 25% of the normal US population is positive as well so a negative test is used to exclude hypocretin deficiency.
In some selected cases, especially if Human Leukocyte Antigen (HLA) DQB1*06:02 is positive but the case is unclear, a lumbar puncture may be performed, Cerebrospinal Fluid (CSF) drawn, and CSF hypocretin-1 measured. If CSF hypocretin-1 is below 110 pg/ml, the diagnosis is consistent with narcolepsy caused by hypocretin deficiency. This particular test was first developed at Stanford and is the most definitive test for narcolepsy. Other radiological, genetic or biochemical tests may also be ordered in selected cases.
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