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Narcolepsy – Testing

October 30, 2020


The next morning after we know they’ve gotten at least six hours of sleep. So we think they’re adequately rested from an average viewpoint. We do an MSLT a mean sleep latency test. It’s normal to take five to 20 minutes to fall asleep, but we asked narcoleptics well, people we think might be narcoleptic to take this test the night after their polysomnogram. And we give them an opportunity to sleep and nap opportunity. Once at eight o’clock in the morning, 10 o’clock in the morning, noon, 2:00 PM and 4:00 PM, five different opportunity to sleep and in between their naps or opportunities to sleep, they’re allowed to get up, roam around, eat breakfast, take a shower, have lunch, but they’re not allowed to jump up and down and be too stimulated with exercise. They’re not allowed to have caffeine or any stimulating drug, and then they’re invited to sleep.

And what would be average is to maybe take a snooze in the middle of the afternoon at a sleepy time of day, such as a two o’clock or four o’clock nap, but we see how quickly they fall asleep. Often narcoleptics can fall asleep within minutes, less than three minutes of being given this 20 minute nap opportunity. What clinches the diagnosis is not just falling asleep during an app, how, but how quickly they do so. And if they fall into a REM period for the rest of us, unless we’re grossly sleep deprived, we’d never have a dream in a 20 minute nap, but patients who fall asleep and go into a dream, a sleep onset REM period, go right into a dream with their nap, at least two out of those five times, clinches the diagnosis for narcolepsy. That’s very unusual after that. If there is a confusion, because sometimes other things get in the way and we still can’t quite interpret our results.

We may consider even checking for hypocretin levels in the cerebral spinal fluid. This would require a spinal tap. So that’s an invasive procedure. We try not to do that too often, but it can be done. And there’s certain specialized labs across the country who measure these things. We would know a very low hypocretin level would be very, very suspicious for narcolepsy because this is the primary problem in this disease. We sometimes do genetic testing for patients with narcolepsy and cataplexy who have a high relationship with certain genetic markers. But those people who have narcolepsy without cataplexy, it’s hard to tell. And it probably wouldn’t wouldn’t be worth it because those genes are kind of common in society. Anyway. So we have several tests that we look at for narcolepsy, but we put them together to make a diagnosis. And while nothing’s perfect, we get a lot of information. And very few things give us all the symptoms of narcolepsy. Although all of us can have some of them at some time of our lives, but put together with these diagnostic tests, we can have a pretty good clear understanding to make this diagnosis.

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