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“Hypersomnia” can mean excessive daytime sleepiness or excessive night-time sleep or both. “Idiopathic” means that the cause of the hypersomnia is unknown, even after thorough examination and testing of the patient. Automatically eliminated from this category are cases attributable to structural disease of the brain such as tumors, infections, and stroke. But often a “known cause“ doesn’t require understanding the underlying mechanism of the disease (as might said of sleep apnea), but just showing a well-established pattern of signs and symptoms which have earned a specific diagnosis, as with narcolepsy (see Glossary). Where that is the case, idiopathic may mean only that the hypersomnia shows itself in a different fashion than is usual with narcolepsy. As we come to understand or at least label with specific diagnoses more of the sleep disorders, the realm of “idiopathic” disorders is likely to shrink. It carries the sense of a tentative “diagnosis by exclusion” of other, more specific, better-recognized disorders.
The label of idiopathic hypersomnia grew out of the recognition of a characteristic pattern for narcolepsy and the realization that certain patients with hypersomnia, the “idiopathic” group, did not follow this narcoleptic pattern, which includes such features as sleep paralysis (see Glossary), cataplexy (see Glossary), hypnagogic hallucinations (see Glossary), and periods of REM (see Glossary) at sleep onset.
People with hypersomnia who didn’t fit the picture of narcolepsy or some other, more specific type of sleep disorder, were said to have idiopathic hypersomnia. They were thought to show a pattern of their own: non-imperative sleepiness (meaning that they weren’t compelled to sleep even though they felt sleepy), long unrefreshing naps, trouble waking up fully after sleep, and sleep drunkenness (see Glossary). They were also said to have a positive family history of the same symptoms, presence of psychiatric symptoms, and a chronic course with poor response to stimulants.
But further study made the two groups, narcoleptics and idiopathic hypersomnics, seem not always so distinct. For example, narcoleptics don’t always have cataplexy or sleep-onset REM periods. This study took a closer clinical look at patients labelled with ”idiopathic hypersomnia.”
The authors started with a database of more than 4000 patients evaluated from 1986 to 1995 at the University of Michigan’s Sleep Disorders Center. Among these, they found 63 (1.5%) diagnosed with idiopathic hypersomnia. They excluded patients initially given this diagnosis who were later found to have Upper Airway Resistance Syndrome (see Glossary) and respond to CPAP.
They examined the records of these 63 patients for the following characteristics intended assure the presence of persistent excess sleepiness and to eliminate cases of narcolepsy, obstructive sleep apnea, periodic leg movements of sleep, voluntary sleep restriction, and other causes of hypersomnia:
(1) excessive daytime sleepiness for more than a year;
(2) absence of definite cataplexy;
(3) mean sleep latency less than 10 minutes on the Multiple Sleep Latency Test or MSLT (see Glossary);
(4) no sleep-onset REM periods during the MSLT naps;
(5) an Apnea/Hypopnea Index (see Glossary) less than 10;
(6) a periodic leg movement index of less than 20 per hour;
(7) no improvement with increased night-time sleep;
(8) no other apparent cause for sleepiness.
The authors note that the criteria above are similar to the criteria for Idiopathic Hypersomnia in the International Classification of Sleep Disorders. The ICD, however, requires a symptom duration of only six months, specifically excludes cases beginning within 18 months of a head injury (implicitly excluded in criterion #8), and is less strict with respect to other criteria. That is, the ICD requires that the patient meet only one of five criteria: short sleep latency on the MSLT (#3), no more than one sleep onset REM period (#4); a sleep latency on the PSG less than 10 minutes; a normal REM sleep latency; or a sleep episode on the PSG that is normal or prolonged in duration.
In fact, the authors eliminated 21 patients because of various of their criteria, most commonly an AHI greater than 10 (in 9 patients) suggesting obstructive sleep apnea. This left 42 patients in their study group. They compared these with 67 narcoleptics, 28 of whom lacked cataplexy. They relied on data from past clinical records but made efforts to contact all patients with idiopathic hypersomnia and succeeded in interviewing 28.
They created a scale to measure five characteristics of idiopathic hypersomnia with the following features: (1) sleep attacks not irresistible; (2) naps usually longer than an hour; (3) naps & sleep hard to terminate; (4) naps unrefreshing, with confusion on awakening; (5) stimulants are ineffective.
Their subjects, whose average age at diagnosis was 35, had onset of symptoms at an average of 19 (SD=+/-8 years). Often this worsened for several years. Females predominated (27:15). Almost all had problems driving and most also had problems at work or in socializing due to sleepiness About 60% took at least one nap a day, which lasted longer than a half-hour in 51%, accompanied by recalled dreaming in 40%, and were unrefreshing in 77%. Almost half had restless sleep with frequent arousals. Only 25% had prolonged nighttime sleep twice or more a month. Difficulty awakening was present in 55% but only 21% reported sleep drunkenness.
PSGs showed short sleep latencies (ave 6.4 mins, SD=+/-6) but were otherwise normal. MSLT sleep latency was shortened but not as much as in narcoleptics.
Compared to narcoleptics, the idiopathic hypersomnics were less often black (7% vs. 27%). The idiopathic hypersomnics less often had the blood antigens (DR2 and DQ1) associated with narcolepsy (33% vs. 72%).
In 24% of the idiopathic hypersomnics, a possible cause was identified: viral illness near the time of onset, head trauma, mood disorder, family history of narcolepsy. Esophageal pressure monitoring suggested UARS in five, all habitual snorers, but none improved with CPAP. After three years, 72% had experienced a good response to stimulants though the mean sleep latency on MSLT usually remained abnormal. Spontaneous improvement (without obvious cause) occurred in 26%, including all 4 with onset after viral illness.
The authors felt they could identify three patterns among these patients. The first was “classic” idiopathic hypersomnia, affecting 8, with sleepiness that was not overwhelming, long unrefreshing naps (up to 4 hours), prolonged nighttime sleep, difficulty awakening, and occasionally sleep drunkenness and excessive nighttime sleeping. Most had psychiatric symptoms and family histories of diabetes. Three of five who tried stimulants improved.
The second type they called “narcoleptic”-like idiopathic hypersomnia, present in 9 patients. These experienced overwhelming daytime sleepiness and took short, refreshing naps from which they awakened without difficulty. Good results were obtained in all seven tried on stimulants.
The third type, called “mixed” idiopathic hypersomnia, included 11 patients with intermediate clinical features such as brief, unrefreshing naps. Five out of nine improved with stimulants.
The authors’ findings, which I have described in considerable detail, led them to an extensive discussion, which I will abbreviate. They noted the diminishing frequency of idiopathic hypersomnia as a diagnosis corresponds to increasing awareness of identifiable causes of excessive daytime sleepiness. It now appears to be much less frequent than narcolepsy, perhaps as low as 2-5 per 100,000 in the Caucasians and even lower in blacks. They noted that psychiatric symptoms of anxiety and depression were common in this group but usually did not follow a parallel course to the hypersomnia. A few patients may have had a type of “atypical” depression. There appears to be substantial overlap of the idiopathic hypersomnic group with narcoleptics, meaning that many did not clearly distinguish themselves from narcoleptics on basis of clinical picture. However, the polysomnography results on the idiopathic hypersomnics were, except for the short sleep latencies, strikingly normal, without any indication of the increased pressure for REM sleep thought by some to underly narcolepsy. The authors questioned this theory and thought that increased REM pressure might represent only one of several elements of narcolepsy, which could separately or in varying combinations.
The authors noted the generally good response of about three-quarters of these patients to stimulants, contrasted to previous reports of poor response. The most dramatic responses occurred in those with the “narcoleptic” type of idiopathic hypersomnia. In contrast, prolonged sleeping did not help their sleepiness at all. In contrast to the almost invariable chronicity of narcolepsy, a quarter of the patients with idiopathic hypersomnia improved spontaneously after a year or more.
The authors concluded by proposing a reclassification of narcolepsy and idiopathic hypersomnia so as to recognize that narcolepsy could occur not only without cataplexy but also with evidence short REM latency or sleep-onset REM periods. This would then further diminish the dwindling size of the remaining category of “idiopathic” hypersomnia.
I have made this a long summary, in part because of the large mass of clinical observations which make up the bulk of the paper, and in part because there are few recent papers on this subject. I will not prolong this further with a lengthy discussion of my own. Those who already know themselves to have sleep apnea or who have symptoms typical of sleep apnea may question the relevance of a much rarer diagnosis which seems to exclude sleep apnea.
Where this may be relevant is in the case of a sleep apneic who has persistent symptoms of excessive daytime sleepiness despite as extensive and proper treatment as can be provided for the apnea, meaning in spite of apparently controlled apnea. Such an occurrence is not all that uncommon, probably more so in less academic settings than the University of Michigan or Stanford. Often it may represent a misread sleep study, insufficient testing, improper adjustment of pressure, poor fit of the CPAP mask, poor compliance, coexisting conditions like periodic leg movements of sleep or even narcolepsy. It seems that, given thorough examination, it will rarely come down to the ambiguous diagnosis of “idiopathic,” which is scarcely a diagnosis at all but more of an admission of inability to make a diagnosis.
It is reassuring to learn that such essentially undiagnosed people may nevertheless respond well to stimulants and an important reminder of the utility of these medicines when doctors are becoming increasingly reluctant to prescribe them. Indeed, they may be useful for sleep apneics with persistent sleepiness while other treatments are tried and adjusted, in order to minimize or curtail disability. In general, however, these idiopathic hypersomnics appear to have a closer relationship to those with narcolepsy (which can, however, coexist with sleep apnea) than to those with obstructive or central sleep apnea or UARS. It is also helpful to remind outselves that, while sleep medicine has made great progress in recent years, particularly with disorders causing excessive daytime sleepiness, there are still individuals suffering from quite disabling EDS for which the cause remains a mystery.
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