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Compared to narcolepsy, which is characterized by well-defined clinical, polysomnographic, and immunogenetic features, idiopathic hypersomnia is not delineated, and its history is much more recent.

Because of the somewhat vague limits of idiopathic hypersomnia and its relative rarity, no prevalence study has been conducted. The only available data are the ratios of idiopathic hypersomnia to narcolepsy in different sleep disorders populations. These ratios tend to decrease in the successive reports, probably due to the use of more stringent criteria, with the notable exception of Aldrich’s recent series.

What is idiopathic hypersomnia?

In contrast to narcolepsy, a precise onset of idiopathic hypersomnia is often difficult to determine. It is because of the insidious beginning of the condition and the difficulty in young persons of settling a posteriori a limit between long sleep and abnormally long sleep, or normal wakefulness and impaired wakefulness. As is the case for narcolepsy and the Kleine-Levin syndrome, onset of this condition is most often during adolescence and rarely after the age of 30 years.

Symptoms of idiopathic hypersomnia

Symptoms may vary with the most typical form referred to as poly-symptomatic. It is mostly characterized by excessive daytime sleepiness, leading to un-refreshing prolonged naps, nocturnal sleep of long duration, as much as 12 hours or more, as well as sleep drunkenness. Subjects affected with this type of idiopathic hypersomnia often refrain from naps. It is mainly due to their spontaneous long duration and their un-refreshing nature. They use sophisticated alarm clocks and often report drinking a cup of strong coffee before being able to take a shower, where almost 19 out of 32 disclosed this set of symptoms. In other cases, subjects complain of excessive daytime sleepiness, have naps of shorter duration that may be refreshing or non-refreshing, and do not report abnormally long sleep or sleep drunkenness as others do.
This set of symptoms represents a more heterogeneous form of the condition and it would not be a surprise if conditions other than idiopathic hypersomnia were identified in these subjects with more sophisticated methods of evaluation. In addition, some patients report headaches, which may be migraines, fainting episodes, orthostatic hypotension, and peripheral vascular complaints of the Raynaud type. Hypnagogic hallucinations and sleep paralysis may be encountered occasionally in these patients. In addition, idiopathic hypersomnia is a life-long disorder with no tendency of spontaneous remission, with complications that are mostly social and professional. It has not been investigated whether a subject’s symptoms can be temporarily alleviated by having their sleep extended.

Diagnosis of idiopathic hypersomnia

The diagnosis of idiopathic hypersomnia is mainly based on clinical features and the absence of associated symptoms, where important symptoms are cataplexy, snoring at night, periodic leg movements, or depression. Polysomnography and some other tests are necessary to rule out other sleep disorders with similar symptoms. Indeed, idiopathic hypersomnia is one of the most over-diagnosed sleep disorders in the world. The most widely used polysomnographic procedure is nocturnal sleep recording followed by a multiple sleep latency test known as MSLT. This procedure shows sleep of normal quality with few awakenings and a normal proportion of different sleep stages. Sleep apneas, restless legs, and periodic movements in sleep are absent where MSLT usually demonstrates a mean sleep latency lasting less than 10 minutes. It may be that subjects with very long nocturnal sleep episodes and sleep drunkenness do not show very short sleep latency on the MSLT, so sleep-onset REM periods are uncommon for these people. The diagnostic value of the MSLT is somewhat questionable in subjects with the poly-symptomatic form of the idiopathic hypersomnia. However, in these cases, awakening the subject early in the morning for the MSLT precludes documentation of the prolonged nighttime sleep, and the MSLT protocol precludes the recording and observation of prolonged daytime sleep episodes. Therefore, it is more useful to perform an all-night sleep poly-graphic recording followed by an MSLT, and after that, it is recommended to follow recording from 7:00 PM onward, doing a 24-hour continuous poly-somnography. It could be done at home with an ambulatory system or in the laboratory on an ad-lib protocol. Using this approach in a group of 19 patients with poly-symptomatic idiopathic hypersomnia, doctors found that total sleep time was 819.50 minutes. Despite some reports that suggest an increased frequency of human leukocyte antigen or HLA, typing is of no help in the positive diagnosis of idiopathic hypersomnia. Psychological interview and tests are appropriate to exclude a neurotic hypersomnia, although CT scan or MR imaging of the brain is indicated when a structural brain lesion is a consideration.

Differential diagnosis for idiopathic hypersomnia

Idiopathic hypersomnia is probably one of the most frequently over-diagnosed sleep disorders, as you already know. This is because there is a tendency to classify in this category all hypersomnias that do not fit the criteria of either narcolepsy or the sleep apnea syndrome. Indeed, the difficulty does not stem from disorders of excessive daytime sleepiness, such as narcolepsy or the obstructive sleep apnea syndrome. These disorders are identified easily with help of their clinical and poly-somnographic features. Contrary, in idiopathic hypersomnia, it comes from other disorders associated with excessive daytime sleepiness that require more sophisticated investigation or that still are delineated insufficiently both clinically and polys-omnographically. The first diagnosis to consider is the upper airway resistance syndrome for suspected people. Excessive daytime sleepiness is a frequent feature while other symptoms include heavy snoring occurring more so in men than in women. Disrupted nocturnal sleep and bruxism are present frequently during sleep, which could help with diagnosis as well. Men and women are affected equally with this disorder. Obesity is uncommon in this condition, but anatomic abnormalities include a triangular face, a high and narrow arched palate, and a long uvula, a class II malocclusion of the mouth and retro-position of the mandible. Polysomnographic recording shows short alpha electroencephalographic arousals lasting 3 to 4 seconds. The presence of increased airway resistance during sleep requires the monitoring of esophageal pressure in purpose to measure trans-pleural pressure. Quantification of airflow using a facemask with a pneumotachometer for the calculation of tidal volume is also helpful. However, the tight-fitting mask may affect sleep continuity. The most typical pattern is an EEG arousal occurring after a sequence of breaths, with progressively increasing inspiratory efforts indicated by progressively more negative peak end inspiratory pressure at Pes measurements and simultaneous decrease in tidal volume, when is compared with preceding breaths, and not accompanied by increased effort. Narcolepsy without cataplexy, also referred to as monosymptomatic, independent, ambiguous, or atypical narcolepsy, or more recently as hypersomnia with sleep-onset REM periods, is clinical variant of narcolepsy. In this narcolepsy, cataplexy is not yet manifest or will not ever manifest.

Types of idiopathic hypersomnia

Idiopathic hypersomnia associated with dysthymia and related mood disorders is a frequent alternative diagnosis.
The complaints of such patients are similar to those of patients with any other hypersomnia. However, its onset is usually later in life, and interview and personality tests point to low-grade, chronic depression or an inability to cope with stressful situations. The MSLT often does not demonstrate short mean sleep latency. The chronic fatigue syndrome is characterized by persistent or relapsing fatigue that does not resolve with bed rest with several minor symptoms often associated. Hypersomnia that develops after a viral infection, such as atypical viral pneumonia, mononucleosis, or Guillain-Barre syndrome, usually develops within weeks or months after the infection started. Individuals complain of fatigue and somnolence and may sleep most of the 24-hour day with favorable outcome, but the resolution may take months or years. Post-traumatic hypersomnia may mimic idiopathic hypersomnia closely, and it develops 6 to 18 months after head trauma. Similar to any other hypersomnia, excessive daytime sleepiness may be the first symptom of progressive hydrocephalus in the absence of other features of hydrocephalus.

Treatment of idiopathic hypersomnia

Treatment of idiopathic hypersomnia has produced results far from satisfactory. Stimulant drugs, such as Dextroamphetamine, Methylphenidate, Mazindol or Pemoline are the most commonly prescribed medications. These drugs often are less effective in idiopathic hypersomnia than in narcolepsy. Moreover, in some cases they are not equally well tolerated. Recently a new compound, Modafinil, the mechanism of which is still unclear, has produced good results in subjects with idiopathic hypersomnia although a double-blind controlled study has not yet been done. In contrast with narcolepsy, naps may not be refreshing for patients with idiopathic hypersomnia and consequently patients avoid napping.


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