Idiopathic Hypersomnia

What is Idiopathic Hypersomnia, how is it diagnosed and what should patients know about it?


One could be chronically sleepy for one or both of the following reasons:

  • There is something wrong with sleep that makes it non-refreshing.
  • There is a problem with the brain mechanisms which normally should keep one alert (whether caused by primary problems within the brain or its chemistry, or by other factors (such as sedating medications or thyroid problems).

The most common causes of severe sleepiness beginning or progressively worsening in adults are SLEEP APNEA and RELATED BREATHING DISORDERS DURING SLEEP.

If the problem instead is a primary disorder of brain chemistry, NARCOLEPSY is the leading diagnosis. As outlined elsewhere on this web site, people with narcolepsy are diagnosed either by a clear-cut history of their having had cataplexy, or via their demonstrating REM sleep in two or more daytime naps on a Multiple Sleep Latency Test.

(The latter test is not 100% reliable, since some patients with classic narcolepsy may not demonstrate REM sleep during any of the naps on a given day, simply by chance).

-Idiopathic hypersomnia (or hypersomnolence. as it has been called) is a diagnosis applied to people who are excessively sleepy–but not because there is anything apparently wrong with their sleep, and not because of narcolepsy or any other identifiable cause.

It is basically a diagnosis of exclusion: one that is made by excluding all other possible diagnoses.

-Idiopathic is a more dignified way of saying that we don’t know exactly what causes the problem.

-Hypersomnia is not the commonest diagnosis…but it is not rarely made, either.

-Hypersomnia does not appear to be one single entity. Various abnormalities of brain chemistry have been suggested in studies of such patients or suspected as being potential causes.

The brain is complex to the point that there would be many different possible ways to impair alertness.

What are three common features of patients diagnosed with idiopathic hypersomnia?

1. People given this diagnosis are likely to sleep for long periods of time without feeling refreshed. They often do not feel any better after taking naps.

It has been said that a history of not feeling refreshed after sleep will reliably differentiate sleep apnea and hypersomnia from narcolepsy, but I personally don’t believe it. I have a number of patients with definite narcolepsy who find naps unrefreshing, and who also wake up feeling groggy and exhausted in the morning.

2. People with idiopathic CNS hypersomnia often have family histories of this same sort of problem, of true narcolepsy or of both entities. Not infrequently, hypersomnia seems hereditary.

3. For the most part, patients diagnosed as having idiopathic hypersomnia report that their sleepiness began late in childhood, during their teen years, or in their early twenties.

Idiopathic hypersomnia resembles narcolepsy in its typical age of onset. For this reason, I am hesitant to make this diagnosis in people who develop sleepiness later in life. There is a greater possibility that people with late onset of sleepiness instead suffer from a specific underlying cause: one that should be identified and managed with specific treatment. They deserve a thorough evaluation.

IMPORTANT! There is one specific condition that is the underlying cause of sleepiness in many patients who are mistakenly diagnosed as having idiopathic hypersomnia: and this condition can be easily overlooked during sleep laboratory testing.

This condition is extremely treatable: so it should always be looked for.

-It is called UPPER AIRWAY RESISTANCE SYNDROME. It refers to patients who may never stop breathing at night, and who may get every breath they attempt but at a high price. People with this syndrome have to work extremely hard to keep air moving through a narrowed upper airway.

In fact, in some cases, the resulting swings in pressure inside the chest have even caused collapse of the left side of the heart!

People with this have been found to be just as likely to fall asleep at the wheel as are people with full-blown sleep apnea.

-The reason that this condition is frequently missed relates to the way that breathing is traditionally monitored in sleep laboratories. Many sleep centers lack the equipment to go any further when indicated to confirm this diagnosis.

Normally, during a conventional sleep recording, one records air flow at the nose and mouth with a temperature sensor, and breathing effort is monitored with bands, strain gages or electrodes on the chest wall and abdomen.

Upper airway resistance syndrome tends to be missed because first, air flow at the mouth and nose are not interrupted (since the person does not actually quit breathing). Second, it is difficult to see increased effort with the type of monitoring just described: since those techniques are very qualitative and not quantitative. They give a rough idea of the breathing effort present without actually measuring it.

The definitive way to diagnose this problem is by monitoring pressure swings within the chest. This in turn is usually done by having the patient swallow a small balloon by which one measures pressure swings. Changes in pressure in the esophagus reflect changes of pressure within the chest, since the esophagus passes through the chest. It is a very simple and safe technique. Unfortunately, most sleep centers do not offer it at this point in time.

-Some individuals with upper airway resistance syndrome snore loudly: which can help to suggest this diagnosis. However, some patients with upper airway resistance syndrome are not loud snorers at all.

-If upper airway resistance syndrome is present and accounts for the patient’s sleepiness, a rental trial of positive airway pressure (CPAP or bilevel PAP) can help confirm such.

Restoration of good alertness on PAP certainly does not favor either narcolepsy or idiopathic hypersomnia, since neither of the latter respond to administration of air under pressure!

-If in fact, upper airway resistance syndrome is not present and if the diagnosis truly is idiopathic CNS hypersomnia, the treatment is very similar to that used for the sleepiness of narcolepsy. Both avoidance of aggravating factors and medications are needed.

In summary, the first step:

Ensure as firm a diagnosis as possible, with careful exclusion of alternative explanations for sleepiness–particularly upper airway resistance syndrome (UARS). Ensure that the sleep center that has evaluated you is capable of doing special monitoring for detection of UARS.

The second step:

Institute the most specific and safest treatment plan possible, utilizing common sense measures to render treatments optimally effective.

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