Although rare, the diagnosis of idiopathic hypersomnia is most often made in the presence of hypersomnias not related to sleep apnoea syndrome or narcolepsy.
Idiopathic hypersomnia is a rare condition, 5 to 10 times rarer than narcolepsy.
Because of these relatively recent diagnostic criteria and its rarity, no epidemiological studies have been conducted.
The age of onset of the disease is often before 30 years. Familial forms are common.
The cause(s) of this condition are not yet known.
Few studies have been carried out on this subject, but it seems that this condition is not linked to hypocretinergic cell hypofunction (neurons in the laterodorsal part of the hypothalamus) nor is it predisposed to HLA typing.
Idiopathic hypersomnia is clinically characterised by more or less permanent excessive daytime sleepiness, with the subject complaining of rarely being fully awake.
The other typical symptoms of narcolepsy, namely cataplexy, sleep paralysis and hypnagogic hallucinations, are not present.
The polysymptomatic form
The polysymptomatic form, or with increased total sleep time, is characterised by :
- abnormally long night sleep (more than 10 hours)
- major inertia on waking from night sleep
- naps (marked by sleepiness with associated slowness of ideation*)
- excessive daytime sleepiness with bouts of sleep lasting more than 1 hour that is never restful
The sleep attacks are less irrepressible than in narcolepsy. Night-time sleep is always of good quality with very few awakenings or intra-sleep micro-arousals.
* Ideation: the mental activity of forming and linking ideas.
The monosymptomatic form
The monosymptomatic form, or without an increase in total sleep time, is of more questionable individualization, characterized by :
- normal night sleep (between 6 and 10 hours)
- frequent bouts of daytime sleep
The duration and restorative nature of these bouts of daytime sleep suggest some clinical similarities with narcolepsy without cataplexy.
Sleep recording is essential to rule out another cause of hypersomnia, such as nocturnal ventilatory disease, periodic limb movement syndrome, etc.
In case of doubt, and in particular if there are many microarousals, a new polysomnographic recording with measurement of the oesophageal pressure will be carried out to eliminate an upper airway resistance syndrome.
The night-time sleep recording will be followed by iterative sleep latency tests to confirm the diagnosis of hypersomnia (mean sleep latency of less than 8 minutes or even 10 minutes in the case of polysymptomatic forms, without REM sleep).
However, this test requires an induced awakening at around 7:00 a.m., thus not allowing the very late spontaneous awakening to be observed.
It is therefore often necessary to carry out a second sleep recording over a period of 24 or 48 hours in order to confirm this diagnosis, in order to highlight the abnormally long duration of sleep, one or more long naps with a total duration of sleep well in excess of 12 hours over the 24 hours of recording.
Brain imaging should be discussed according to the clinical context.
Finally, personality tests are sometimes necessary to exclude hypersomnia of psychiatric origin.
The treatment of idiopathic hypersomnia involves the use of modafinil as a first-line treatment, which is particularly effective in this condition.
If this fails, mazindol or methylphenidate may be of interest.
However, the inertia of the alarm clock is often poorly controlled.