Idiopathic hypersomnia: symptoms, diagnosis and treatment in the UK

Hypersomnia means excessive daytime sleepiness that happens no matter how well or for how long someone sleeps. Royal Papworth Hospital explains that when excessive daytime sleepiness is confirmed by clinical assessment and sleep testing, it often turns out to have an underlying cause. Sometimes no cause is found for a person's obvious sleepiness, and in such cases the diagnosis of idiopathic hypersomnia is often appropriate.

Narcolepsy UK, a charity that also supports people with this condition, describes idiopathic hypersomnia (IH) as a related sleep disorder that shares some features with narcolepsy but is a distinct condition.

Narcolepsy UK says people with IH can have an unusually long night's sleep, sometimes of 11 hours or more, yet on waking do not feel refreshed. Many experience prolonged periods of confusion, disorientation and irritability called sleep inertia, a foggy state of mind that can last for several hours.

They may also be struck by excessive daytime sleepiness and need to take naps during the day. During periods of sleepiness, it is not uncommon to experience automatic behaviour, which means carrying on an activity without being fully aware of it afterwards.

Like narcolepsy, symptoms can appear at any age but onset occurs most frequently during the teens, and the same source says IH can have a similarly damaging effect on schooling, work and relationships. For that reason it stresses the importance of getting a diagnosis and treatment as soon as possible after the symptoms begin.

• Sleepiness during the day despite long or good-quality sleep.

• Long night-time sleep, sometimes 11 hours or more.

• Waking unrefreshed, with confusion, irritability or fog lasting hours (sleep inertia).

• A need to nap during the day.

• Automatic behaviour during periods of sleepiness.

Narcolepsy UK says that, as with narcolepsy, diagnosis will usually require an overnight sleep test and a multiple sleep latency test (MSLT) in a specialist sleep clinic. Royal Papworth Hospital adds that excessive daytime sleepiness is confirmed on the basis of clinical assessment and sleep testing, and that the diagnosis of idiopathic hypersomnia is considered when no cause for it is found.

In practice this means other explanations are looked for first. Royal Papworth's advice for the next step is to consult your GP, who can refer to a sleep service. A sleep diary and information from a partner or family member about your sleep and behaviour can be useful for the specialist, though the formal tests are what establish the diagnosis.

There is currently no cure, but treatment does exist. Royal Papworth Hospital says treatment takes the form of medicines to increase the level of alertness during the day, and that these are frequently effective and generally well tolerated. Narcolepsy UK names wake-promoting medicines such as modafinil and stimulants such as methylphenidate.

Lifestyle changes can also help, although Narcolepsy UK says they can be particularly challenging to implement for people with IH. Because medicine choices, dosing and monitoring are individual and decided by a specialist, this guide does not give doses.

Because the sleepiness is unrelenting and not relieved by sleep, school, work and relationships can all be affected, which is why Narcolepsy UK emphasises early diagnosis. Practical steps include explaining the condition to employers or schools, asking for adjustments, and planning demanding tasks for the times of day when alertness is better.

Safety matters. Excessive sleepiness can make driving unsafe, and anyone with it should take specialist advice about driving and tell the DVLA if their doctor advises it. Narcolepsy UK offers information and support to people with idiopathic hypersomnia, and also points to the Hypersomnia Foundation, an American charity with global outreach.

On the NHS, the usual route is from the GP to a sleep or respiratory service with a specialist sleep clinic. Overnight sleep studies and MSLT testing are done in specialist centres, and waiting times can be long because few centres offer the full set of tests.

Private sleep clinics also exist and may offer quicker assessment, and some people choose them for a second opinion. The tests and medicines are broadly the same, so the difference is mainly in speed and in who coordinates long-term follow-up. Ask which clinician will manage the prescriptions over time.