Summary

Idiopathic hypersomnia (IH) poses a significant challenge for individuals experiencing excessive sleepiness without a definitive cause. While researchers delve into potential theories such as GABA-A receptor activation and circadian rhythm disruption, the exact origins of IH remain unclear. It is crucial to differentiate between IH and chronic fatigue syndrome to provide accurate diagnoses and tailored treatment plans. Future research endeavors aim to uncover novel insights and therapeutic strategies to improve the management of idiopathic hypersomnia.

Idiopathic hypersomnia (IH) is a rare neurological disorder. Treatment can help, but there is no cure. You may sleep more than 9 hours a night without feeling refreshed. You may have difficulty waking up in the morning. Your sleepiness may persist or worsen, even when you take long naps during the day.

If you live with HI, you would probably like to know what is causing your symptoms. Unfortunately, that's not something experts have figured out yet.

“Literally, the name idiopathic hypersomnia means that you're sleepy and we don't know why,” says Sabra Abbott, MD, assistant professor of neurology and sleep medicine at Northwestern University Feinberg School of Medicine in Chicago.

Many sleep specialists are trying to solve the IH puzzle, including Dr. Lynn Marie Trotti, associate professor of neurology at Emory University School of Medicine in Atlanta. Sleep disorders tend to run in families, so your genes likely have something to do with it. But Trotti says she and her colleagues still don't know the main source of all this extra sleepiness.

“The big mystery is really what causes idiopathic hypersomnia,” Trotti says.

Theories behind idiopathic hypersomnia

We still don't know why people with HI are so sleepy or why the disorder causes cognitive symptoms such as brain fog, memory problems, or inattention. But thanks to the ongoing investigation, Trotti and Abbott say some clues are emerging, including:

Something activates your GABA-A receptors. These are neurotransmitters that inhibit the central nervous system. Drugs such as benzodiazepines can activate them. Doctors use these types of medications to treat anxiety and insomnia.

Trotti says that people with HI sometimes have higher levels of naturally occurring benzodiazepines in their cerebrospinal fluid. “And the fact that there was a difference suggests that (GABA-A receptors) might be related to sleepiness in idiopathic hypersomnia,” she says.

There is ongoing research into this theory. But Abbott says the idea is that something in the body acts like a sleeping pill throughout the day.

“That's helpful when you're trying to fall asleep, but not when you're trying to stay awake during the day.”

Your circadian rhythm is out of sync. Everyone has a natural sleep-wake cycle. If you have HI, you may stay up late and have a lot of trouble getting up early. This “suggests that there could at least be a component of a circadian timing problem,” Trotti says.

Abbott says he sees a lot of overlap between HI and something called delayed sleep-wake phase disorder. These are your natural night owls who stay asleep and wake up later, she says. While the average circadian rhythm for most of us is a little longer than 24 hours, she says this group operates differently.

“It's like they live a 25-hour day,” Abbott says. “Your sleep period is longer because your internal day is longer. “They are always trying to catch up.”

Chronic fatigue versus idiopathic hypersomnia

Since IH is a bit mysterious, it can go undiagnosed for a long time. It may seem like other conditions. That might have something to do with how we think and talk about sleep. You may hear people use terms like “fatigue” and “drowsiness” interchangeably, but they are not the same.

Here's how Trotti explains the difference: Hypersomnia means you sleep too much or fall asleep when you shouldn't, such as taking naps during the day. Fatigue, on the other hand, is a tiredness or lack of energy that does not usually increase sleep time.

That said, Trotti says that about 20% of people with hypersomnia also have chronic fatigue syndrome. But a careful history of your symptoms can help your doctor figure out what's going on.

They could ask:

• What are your day and night schedules like?
• How much time do you spend sleeping?
• How much time do you spend resting but awake?
• How much time do you spend trying to function while tired?

Sleep tests are also helpful. When it comes to hypersomnia, your doctor will see if:

• You fall asleep quickly during a daytime nap
• You sleep more than 11 hours in a 24-hour period.

Trotti says you wouldn't expect the above symptoms if you have chronic fatigue syndrome without a hypersomnia disorder.

Where is the research going?

Abbott says there is a lot of interest in the GABA hypothesis. Most of the ongoing research focuses on that area because some anti-GABA medications can reverse symptoms in some people with HI. In the future, there may be more medications like this made specifically for IH.

“It's a disorder that we still don't know much about and for which we don't have good treatments,” Abbott says. “But as I tell my patients, there are people who are actively investigating it. Hopefully in 5 or 10 years we will have better answers in terms of what causes it and what treats it.”