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Idiopathic Hypersomnia 101

September 11th, 2023

What is Idiopathic Hypersomnia?
Idiopathic Hypersomnia (IH) is one of the sleep disorders classified as a Central Disorder of Hypersomnolence, as is Narcolepsy Type 2 (NT1) and Narcolepsy Type 2 (NT2). IH is characterized by extreme sleepiness and an inability to stay awake. People with IH experience some of the same symptoms as people with NT1 and NT2.

Symptoms of IH
The most prevalent and frequent symptom is:

People with IH at varying frequencies may experience:

  • Long Sleep Times includes 11+ hours of sleep.

  • Sleep Inertia or “sleep drunkenness” is a severe and prolonged sense of grogginess and disorientation upon waking up from sleep.

  • Unrefreshing Nighttime Sleep and Naps regardless of length do not relieve sleepiness.

People with IH may occasionally experience symptoms that are similar to NT1 and NT2. These symptoms for people with IH are less common:

  • Sleep Paralysis is an inability to move at sleep-wake-transitions.

  • Hypnagogic/hypnopompic sleep-related hallucinations may include vivid audio/or visual events when falling asleep or awakening.

  • Disturbed Nighttime Sleep is fragmented sleep with multiple awakenings.

The cause of IH, as well as NT2, is not yet known. The cause of NT1 has been identified as a loss of orexin (also known as hypocretin) in the brain. Orexin is a neuropeptide that regulates wakefulness and sleep.

Time to diagnosis is long for people with IH. In the publication Sleep Medicine Clinics from 2012, Masri and colleagues reported that patients go undiagnosed or misdiagnosed for 10 to 15 years after the onset of their initial symptoms. IH can only be diagnosed definitively with a set of sleep studies. Your doctor will take a medical history and perform a physical exam. Once other disorders causing sleepiness have been ruled out, diagnosis for IH requires an overnight Polysomnogram (PSG) and a Multiple Sleep Latency Test (MSLT), or evaluation of total sleep time during a 24-hour PSG or by wrist actigraphy. Your doctor may also ask you to keep a sleep diary. If a sleep study is repeated, an IH diagnosis may change to an NT2 diagnosis, and similarly, an NT2 diagnosis may change to an IH diagnosis.

  • PSG – takes place overnight in a sleep lab and monitors brain activity, heart rate, breathing, eye and leg movements, and oxygen.

  • MSLT – occurs after a polysomnogram and gives you a nap opportunity approximately every 2 hours over the course of the day for a total of 4-5 naps. It records the time it takes for you to fall asleep during a nap and what sleep stages you enter.

As of May 2024, there is only one Food and Drug Administration (FDA) approved treatment, which is lower-sodium oxybate. It is a central nervous system depressant that is taken at night and reduces next day sleepiness and sleep inertia. Stimulants are also very often utilized off-label to promote wakefulness. Contacting a physician is an important step in determining an individualized treatment plan.

Clinical Research
A considerable amount of research is being conducted to advance new treatments for people with iH, NT1, and NT2. Research includes wake-promoting agents, and agents that address a loss of orexin in the brain.

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Date Created: September 11th, 2023
Last Updated: May 31st, 2024