What is idiopathic hypersomnia?

Idiopathic hypersomnia (IH) is a rare sleep disorder. People who have IH experience hypersomnia, which means they sleep for long periods of time, but remain extremely tired and groggy during the time they are awake.

Though people with IH may sleep 10 hours or more at night, they frequently have a tough time waking in the morning and from naps. They often have trouble staying wakeful during the day and may experience an overwhelming need to sleep at inappropriate times. Despite the hours that they sleep, they do not feel rested.

The condition can affect many aspects of a person’s life, including work, relationships, and physical and mental health. It can also be dangerous and possibly life-threatening—for example, a person may suddenly grow sleepy while driving a vehicle.

What causes idiopathic hypersomnia?

In medical terminology, the word “idiopathic” refers to a condition that does not have an identifiable cause. As the name implies, the cause of IH is unknown.

Since IH is a rare condition, research is limited. At least in some cases, it is considered a neurologic condition. Some research shows differences in brain structure among people who have IH.

Other research suggests that some people with IH have low levels of histamine. Histamine is a neurotransmitter (brain chemical) that helps regulate the sleep-wake cycle, among many other functions. Some studies speculate that IH may be related to mononucleosis (an infection with the Epstein-Barr virus) and immune system dysfunction.

However, the exact causes of IH remain unknown, and more research is needed.

How is idiopathic hypersomnia diagnosed?

There is no definitive test to determine if someone has IH, and there are many different disorders and conditions that can cause excessive sleepiness.

So, healthcare providers (HCPs) must follow certain guidelines when making an IH diagnosis. Among other criteria, a person must have excessive daytime sleepiness every day for at least three months, and their symptoms cannot be explained by other potential causes. These causes may include:

• Medications
• Mental health disorders, such as depression
• Thyroid disorders
• Head injuries
• Other sleep disorders

Depending on symptoms, personal medical history, and family medical history, diagnosis may involve working with several HCPs with different specialties.

Sleep studies are also helpful in distinguishing IH from other sleep disorders. These studies take certain measurements during nighttime and daytime sleep, including eye movements, blood oxygen levels, heart rate, breathing, body movements, and snoring.

How does IH compare to other sleep disorders?

Hypersomnia can be divided into two categories—primary and secondary. Primary hypersomnia is not linked to another cause or health condition. IH falls into this category. So do two other sleep disorders: narcolepsy and Kleine-Levin syndrome.

• With narcolepsy, a person will fall asleep suddenly and sleep for a few seconds or a few minutes. They feel rested after waking up in the morning but feel drowsy during the day. They may also experience disturbed sleep throughout the night.
• With Kleine-Levin syndrome, symptoms occur in episodes lasting a few days or a few weeks. A person with Kleine-Levin syndrome may sleep 20 hours a day during an episode but sleep normally between episodes.

Secondary hypersomnia occurs as a result of having another health condition. For example, a person may experience hypersomnia because of a head injury, thyroid disorder, or depression.

If you are experiencing hypersomnia or excessive sleepiness, talk to an HCP, who can help diagnose what’s causing your symptoms and help you decide on an appropriate treatment.