Idiopathic hypersomnia (IH) is a chronic neurological disorder marked by an insatiable need to sleep that is not eased by a full night’s slumber. People with idiopathic hypersomnia sleep normal or long amounts of time each night but still feel excessively sleepy during the day. They may take long naps, but wake up feeling no better or worse than when they fell asleep. Check out our IH Summary: Characteristics & Diagnostic Criteria.
What Are the Symptoms of Idiopathic Hypersomnia?
The main symptom of IH is excessive daytime sleepiness despite adequate, or more typically, long sleep amounts (e.g., more than 10-11 hours per night). Additional symptoms and complaints commonly include unrefreshing or non-restorative sleep, and sleep inertia and sleep drunkenness. Sleep inertia/drunkenness is the difficulty awakening from sleep, accompanied by feelings of grogginess and disorientation upon awakening. While people without sleep disorders may wake up and briefly want to return to sleep, in people with idiopathic hypersomnia, this sleep-to-wake transition is much more difficult and prolonged. Sleep seems to leave a mental fogginess, which can remain throughout the few hours that people with IH can remain awake. Thinking clearly and carrying out even basic physical tasks can be difficult.
Many people with IH sleep more than 11 hours out of every 24. The disorder is chronic, and the symptoms can be relentless. If an effective medication to control symptoms cannot be found, it can be extremely difficult for people with IH to hold down jobs, remain in school, maintain marriages, and fully engage with their family and friends. Even with medication, patients may struggle with these activities.
Symptoms often first appear in the mid-to-late teens or early twenties, although they can begin in childhood or at a later age. Symptom intensity often varies (between weeks, months, or years) and can worsen just prior to menses in women. Symptoms may spontaneously remit in 10-15% of patients.
Sleep is usually described as “deep,” and arousal from sleep is usually difficult, often requiring multiple alarm clocks and morning rituals to ensure that patients arise for school or work. In contrast to the short and generally refreshing daytime naps observed in narcolepsy type 1, those naps in IH patients can be very long – on the scale of hours – and are unrefreshing.
Diagnosing Idiopathic Hypersomnia
Proper diagnosis of idiopathic hypersomnia is key to establishing beneficial treatment strategies and includes:
- Presence of excessive daytime sleepiness for at least 3 months
- Excluding prescribed medications as a cause
- A comprehensive medical history, physical examination, and medical tests to rule out other conditions as a cause
Additional Diagnosis Resources:
- UpToDate’s article: “Approach to the Patient with Excessive Daytime Sleepiness“
What Causes Idiopathic Hypersomnia?
IH is a disorder of the nervous system whose cause is not known. In some cases, there appears to be over-production of a small molecule that acts like a sleeping pill (e.g., a sedative-hypnotic drug such as Versed®) or anesthetic (e.g., propofol). Although the exact composition of this small molecule is yet to be determined, much is known about how it interacts with γ-aminobutyric acid (GABA), a principal player in the brain mechanisms that promote sleep. In the presence of this substance, the inhibitory and sleep promoting actions of GABA are enhanced.