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A new study looks at how many people may have the sleep disorder idiopathic hypersomnia. skynesher/Getty Images
  • Extreme daytime tiredness and long hours of sleep are indicators of a rare sleep disorder.
  • New research indicates the disorder, known as idiopathic hypersomnia, may be more common than prior estimates indicated.
  • The disorder is still not well understood and is difficult to diagnose.

A rare neurological disorder that is characterized by debilitating daytime tiredness and excessive sleeping could be far more common than previously thought.

Idiopathic hypersomnia (IH) isn’t just another sleep disorder; in fact, the very name itself, “idiopathic,” means that its cause is unknown.

Similar to other sleep disorders, like narcolepsy, it results in sleepiness that is so powerful that it can affect your ability to function normally. It is also hard to diagnose, as people must have significant symptoms for three months before being considered to have the condition.

Once a physician suspects this diagnosis, they must use specialized equipment and a laboratory setting for a sleep study for confirmation. Because of this, experts have a hard time estimating the number of people dealing with IH.

But that is changing. According to new research from the American Academy of Neurology, the condition could actually be affecting a far greater number of Americans.

The research, published this week in the journal Neurology, indicates that as much as 1.5% of the population could have IH.

“The estimated prevalence of 1.5% for IH is on par with other common neuropsychiatric conditions such as bipolar disorder, epilepsy, and schizophrenia,” wrote the study authors. Due to the rigorous requirements of sleep studies, population-based estimates of IH are difficult to ascertain.

“It’s obviously an intriguing study because, as was pointed out in the article, the prevalence of idiopathic hypersomnia has been lower in some other studies. So at 1.5%, it’s definitely significant in terms of how common this disorder might be,” said Dr. Clete Kushida MD, PhD, the Division Chief and Medical Director of Stanford Sleep Medicine at Stanford University. He wasn’t affiliated with the research.

For the study, researchers utilized data from the Wisconsin Sleep Cohort (WSC), an ongoing longitudinal study that has been running for over 20 years. To develop a picture of how pervasive IH is among the general population, the researchers analyzed the data from nearly 800 participants in the WSC.

From that cohort, only 12 were identified as likely having IH, which resulted in the finding of a prevalence of 1.5%.

While generally in agreement with the findings, other experts who reviewed the study were hesitant at such a high figure.

“Looking at the paper, I agree that idiopathic hypersomnia is under-recognized. I don’t know that it’s quite that frequent, 1% is really high,” Dr. Mark Wu, MD, PhD, a Professor of Neurology and Sleep Medicine at Johns Hopkins University, told Healthline.

Wu wasn’t affiliated with the study.

“You really have to do a careful job of teasing apart all kinds of things that could be contributing to this. So I think the way I look at that paper is, hey, 1% of people out there are really sleepy. And then probably a subset of them have idiopathic hypersomnia,” he said.

Participants were identified as likely to have IH based on criteria like sleepiness, amount of sleep, and how long they took to get to sleep. The study utilized an array of methods, including in-laboratory sleep studies and questionnaires, to assess sleep disorders and their symptoms.

The Epworth Sleepiness Scale is a self-reported questionnaire in which people are asked to answer how likely they are to fall asleep in various situations like watching TV or reading. The highest possible score is 24 points, but anyone scoring 10 or greater could have a potential sleep disorder”

“Anything over 10 is considered abnormal,” said Wu.

The study found that those with IH had an average score of 14, compared with an average score of 9 for those that did not have the condition.

Participants in the Wisconsin Sleep Cohort also underwent laboratory sleep studies involving polysomnography, which records body functions, including heart rate, eye movement, and brain waves during sleep.

They also participated in “multiple sleep latency” tests, sometimes called nap tests. During nap tests, participants are repeatedly instructed to try to nap at various points during the day. How quickly they fell asleep was indicative of greater sleep latency.

During the sleep study and nap tests, those who likely had IH took only 4 minutes to fall asleep at night and 6 minutes during naps. The average for the rest of the cohort was 13 minutes to fall asleep at night and 12 minutes during naps.

IH is uniquely different from narcolepsy, a more common and well-understood sleep disorder. Narcolepsy is caused by a deficiency in the brain chemical hypocretin (orexin). The cause of IH is unknown and may be the result of multiple different causes.

And here’s the real kicker: getting more sleep doesn’t appear to help.

Not only does IH cause daytime sleepiness, but it appears to be unaffected by how much sleep you get. In fact, people with IH tend to sleep more, not less, than healthy people. Lack of sleep isn’t the problem, instead, people with IH don’t feel refreshed or wakeful after sleeping, even if they’ve gotten more than the recommended eight hours.”

“Patients with idiopathic hypersomnia, when they wake up in the morning, they feel really drunk. They feel like they have this mental fog, and they cannot clear their head for like an hour or two hours. The other thing that they find in contrast to narcolepsy patients, they do not find brief naps refreshing. So, if you take a patient with idiopathic hypersomnia and you give them a brief nap, they don’t feel better. In contrast, a patient with narcolepsy, if they get a brief nap, they do feel better,” said Wu.

“If on a consistent basis [sleepiness] is impairing your ability to do your job or do your activities in your house or at home or for pleasure, then I think it’s time to consider seeing a sleep medicine physician. You could start by seeing your primary care physician, and they could make the referral, or you could just directly make an appointment with the sleep medicine physician,” said Wu.

Both Wu and Kushida encourage individuals who believe they are having sleep problems to speak with their healthcare provider.

Sleep disorders like sleep apnea are far more common and much easier to treat than IH.

“If you’re sleeping a really long time, and by long I mean in the range of like 10 to 12 hours per day, and you’re very sleepy still during the daytime, you should definitely have it checked out,” said Kushida.

Wu emphasized that your quality of life is a good barometer for whether you are getting healthy sleep.

Idiopathic hypersomnia is a rare sleep disorder that could actually be much more common.

New research indicates that up to 1.5% of people could have the disorder.

Idiopathic hypersomnia is hard to diagnose, but people who sleep excessively and are also very sleepy during the day should consider speaking to their healthcare provider.