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By Diane Griffith, HealthAtoZ writer
If you're tired - really, really tired - you may have a sleep disorder that often goes undiagnosed. It's a disorder of the brain that affects an estimated 200,000 Americans. Interestingly, it also affects Doberman pinschers and Labrador retrievers. It's called narcolepsy.
Narcolepsy causes attacks of overwhelming daytime sleepiness, even after a normal night's sleep. Unfortunately, these attacks can happen at any time - even when you're working, sitting in a meeting or driving your car.
Symptoms
If you have narcolepsy, aside from being sleepy, you may have any of the following symptoms.
- Hypnagogic hallucinations. Vivid, dreamlike experiences that happen when you're in the state between being awake and asleep. They seem very real and you may "hear" music or "feel" that you have been touched.
- Sleep paralysis. An inability to move, speak or open your eyes when you're in the state between sleeping and waking.
- Cataplexy. Muscle collapse that happens while you're awake. In a mild case, your face or leg muscles may feel weak. In a severe case, you may drop to the floor, unable to speak or move, but still alert and aware. This can last several minutes. Laughter, anger, embarrassment or any emotional experience can cause this to happen.
Causes
While the exact cause of narcolepsy remains unknown, scientists are uncovering some of the mystery. They have identified genes that are strongly associated with the disorder. They have also discovered abnormalities in various parts of the brain involved in regulating REM sleep. These abnormalities appear to contribute to the development of narcolepsy symptoms.
Diagnosis
An estimated 85 percent of people with narcolepsy don't know it because their problems are often blamed on other conditions.
Two tests in particular are considered essential in confirming a diagnosis of narcolepsy: the polysomnogram (PSG) and the multiple sleep latency test (MSLT).
The PSG is an overnight test that takes continuous measurements while you are asleep. It documents abnormalities in the sleep cycle. It records heart and respiratory rates, electrical activity in the brain through electroencephalography (EEG), and nerve activity in muscles through electromyography (EMG). A PSG can help reveal whether REM sleep occurs at abnormal times in the sleep cycle and can rule out the possibility that symptoms result from another condition.
The MSLT is performed during the day to measure the tendency to fall asleep and to tell whether isolated elements of REM sleep intrude at inappropriate times during the waking hours. As part of the test, you are asked to take four or five short naps usually scheduled 2 hours apart over the course of a day. The sleep latency test measures the amount of time it takes to fall asleep. Because sleep latency periods are normally 10 minutes or longer, a latency period of 5 minutes or less suggests narcolepsy. The MSLT also measures heart and respiratory rates, records nerve activity in muscles, and pinpoints the occurrence of abnormally timed REM episodes through EEG recordings. If you enter REM sleep either at the beginning or within a few minutes of sleep onset during at least two of the scheduled naps, this also indicates narcolepsy.
REM and non-REM sleep
When they first fall asleep, most people go into non-REM (non-rapid eye movement) sleep, a relaxed, quiet state. After about 90 minutes, they switch to REM (rapid eye movement) sleep. Their breathing and heart rates become irregular, their eyes move rapidly as vivid dreaming takes place, and their brain waves become similar to when awake.
If you have narcolepsy, you often skip non-REM sleep, going right into REM sleep. You:
- Fall quickly into a deep sleep.
- Awaken suddenly, often feeling disoriented.
- Have vivid, memorable dreams.
- Are extremely tired during the day because of your lack of restful sleep at night.
When we're in REM sleep, our muscles can't move, which keeps us from waving our arms, kicking our legs and "acting out" our dreams. This temporary "paralysis" takes place only during REM sleep. Scientists believe, though, that if you have narcolepsy, this muscle paralysis can be set off when you're wide awake (which would explain cataplexy) or when you are starting to wake up (explaining sleep paralysis).
Dangers
Narcolepsy impairs attention so it increases the risk of mistakes and accidents. In most states, you cannot drive unless your narcolepsy is under control.
Treatment
If you think you have narcolepsy, see your doctor. There is presently no cure, but there are medications that can help you live a normal life.
This article was reviewed and updated June 2007.
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