Idiopathic hypersomnia (IH) is a chronic neurological disorder that results in excessive daytime sleepiness (EDS), frequently accompanied by an excessive need for sleep (ENS) despite long periods of sleep overnight and during the day. 

Common symptoms of idiopathic hypersomnia

The most common symptom of IH is excessive daytime sleepiness despite an adequate, or even very long period of sleep per night. Other symptoms include un-refreshing or non-restorative sleep. Severe sleep inertia or sleep drunkenness, which is extreme difficulty awakening from sleep, accompanied by feelings of grogginess and disorientation upon awakening is also a common symptom.

People with idiopathic hypersomnia experience a more complicated and prolonged sleep-to-wake transition than those without IH who can wake up and feel refreshed. IH can make you feel that despite sleeping you have a persistent mental fogginess, which stays with you throughout the day. Thinking clearly and carrying out even basic tasks can be difficult.

Many people with IH sleep more than 10 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.

Although they can begin in childhood, symptoms of IH often first appear in the mid-to-late teens or early twenties. Symptom intensity usually vary and can worsen just before women’s menses. Symptoms may spontaneously improve in 10-15% of patients.

What causes idiopathic hypersomnia?

IH is a disorder of the brain and central nervous system whose cause is not known. There may be multiple causes, which apply to subsets of the IH population. Research from Emory University showed that in a subset of people with IH, there is an overproduction of a small molecule in cerebrospinal fluid that acts like a sleeping pill or anesthetic in a few cases. Although the exact composition of this small molecule is yet to be determined, it is known to interact with γ-aminobutyric acid (GABA), a principal player in the brain mechanisms that promote sleep. Because of this substance, the inhibitory and sleep-promoting actions of GABA are enhanced.

How is IH diagnosed?

Diagnosis of idiopathic hypersomnia is key to establishing treatment strategies and includes a combination of clinical assessment and diagnostic tests:

  • Clinical assessment:
    • Presence of excessive daytime sleepiness for at least 3 months
    • Comprehensive medical history, physical examinations, and medical tests to rule out other conditions 
    • Excluding prescribed medications which can cause sleepiness
  • Diagnostic testing:
    • Excluding disturbances in sleep rhythms (e.g., circadian sleep disorders) and insufficient sleep (usually assessed via a ‘sleep diary’ in combination with a wearable sensor called an actigraph)
    • An overnight sleep test or polysomnography (PSG), followed by a daytime Multiple Sleep Latency Test (MSLT), ideally performed in a sleep laboratory

How is IH different from narcolepsy?

There are a lot of similarities between IH and narcolepsy. In fact, it can be hard (or impossible in some cases) to differentiate narcolepsy without cataplexy (narcolepsy type 2 or NT2) from IH.

Narcolepsy with cataplexy (narcolepsy type 1 or NT1) includes the core clinical symptom of cataplexy which only occurs in this condition. There are also more sleep boundary symptoms such as sleep paralysis, hypnopompic or hypnogogic hallucinations and sleep disturbance. In addition, people with narcolepsy with cataplexy have low or absent levels of orexin in cerebrospinal fluid (CSF), so if needed, the diagnosis can be confirmed by measuring this. 

However, the symptoms of narcolepsy without cataplexy (narcolepsy type 2 or NT2) are much more similar, and can be hard to differentiate. This has led to alternative proposals, published in the the journals Sleep Medicine Reviews and Sleep for classifying central disorders of hypersomnolence which recognise the uncertainty in this area of both the underlying pathophysiology of NT2 and IH together with their clinical presentations. 

Whilst at the moment, treatment options for NT2 and IH are similar and comprise of symptom focussed approaches, as we advance to developing more precision-based approaches a better understanding of the pathophysiology of these conditions and better ways of differentiating them clinically are needed.

What treatments are used for IH?

Treatments for IH are targeted towards symptoms of excessive daytime sleepiness (EDS) and excessive need for sleep (ENS). Sleep inertia is also a particularly challenging symptom for people with IH. 

  • Non-drug approaches: whilst there isn’t particularly good research in this area, there are a number of strategies that can be helpful to reduce the impact of symptoms
    • Cognitive behaviour therapy (CBT-H) – this is a treatment program currently being developed by Dr Jason Ong from Northwestern University in Chicago. A summary of a pilot study is here
    • Supportive counselling – although IH is not caused by psychological factors, it can be very debilitating for people, which in turn can have negative effects on their mood and mental health. Having a psychologist or counsellor who understands the challenges of IH can be an important source of support for people with IH, particularly when they are first diagnosed. Although this interview discusses the role of a psychologist for people narcolepsy, the same goes for people with IH.
    • Link with patient groups – as IH is uncommon and poorly understood by others, including many health professionals, it is important to link people with IH into groups where others with IH have the opportunity to discuss their experiences. Examples of these groups include:
    • Diet – there is no evidence to support recommendation of a particular diet of foods in IH. In some online forums people report good results from low carbohydrate or ketogenic diets. However these haven’t been shown to be effective in clinical trials. It is important though for people with IH to ensure they have a healthy, well balanced diet, as diets high in carbohydrates and fat have been shown to increase tiredness and sleepiness in a normal population.
    • Avoid sleep deprivation – it is hard for people with IH to know how much sleep is enough, as often they could sleep all day and all night if given the opportunity. But it is important to ensure that people with IH are getting at least the recommended amount of sleep for someone of their age. 
  • Medications: are generally prescribed to help with reducing daytime sleepiness. There are a range of wake promoting medications that are described in detail in this article. They include:
    • Modafinil (Modavigil / Provigil)
    • Armodafinil (Nuvigil)
    • Dexamfetamine
    • Methylphenidate (Ritalin / Concerta)
    • Sodium oxybate (Xyrem / Xywav)
    • Pitolisant (Wakix)
    • Solriamfetol (Sunosi)

Several other medications have also been used, including selective norepinephrine re-uptake inhibitors such as reboxetine (currently in phase 3 clinical trials as a treatment for narcolepsy) and atomoxetine (approved for use in ADHD).

Note – sodium oxybate, pitolisant and solriamfetol are not registered products in Australia. Unregistered products can be prescribed for individual patients via the TGA SAS-B scheme. There is information on prescribing sodium oxybate in Australia in this post.

If I think I have IH, what should I do?

If you think you may have IH, and your sleepiness hasn’t responded to general measures like getting enough sleep and looking after your general health, you should talk to your doctor. They will be able to review your overall clinical history, may arrange tests if they suspect other conditions, and can refer you on to a sleep specialist for assessment. 

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