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Central Disorders of Hypersomnolence 


By Admin


Hypersomnolence is a compound term combining the prefix “hyper,” meaning excess, with the word “somnolence,” meaning sleep or want of sleep. One of the seven major categories of sleep disorders, Central Disorders of Hypersomnolence, or CDH for short, refers to conditions involving sleepiness or fatigue. In some cases, these disorders involve more sleep than is necessary, as opposed to less, which is a sign of more common disorders such as insomnia and sleep apnea. Narcolepsy, for example, involves excessive sleepiness that can lead to very serious problems when patients become tired enough to fall asleep during daytime activities. Like most sleep disorders, hypersomnolence is often associated with other medical or psychiatric conditions, making it difficult to diagnose and treat properly. According to the Hypersomnia Foundation, the socioeconomic burden of these disorders is a serious problem as well, leading to unnecessary costs that could be avoided with further research and better diagnostic tools. While less common than insomnia or sleep-related breathing disorders, these conditions are becoming more common as sleep problems proliferate throughout the world. 


Types of Hypersomnolent Disorders

While the terms hypersomnia and hypersomnolence are often used interchangingly, In clinical terms,hypersomniarefers to specific conditions, while “hypersomnolence” refers to the general symptoms of oversleeping or excessive daytime sleepiness (EDS), regardless of cause. Hypersomnia can be primary (of central or neurological origin), or it can be secondary to any of numerous medical conditions. And more than one type of hypersomnia can exist simultaneously. Often, hypersomnolent symptoms are the result of other sleep disorders as well, such as insomnia or obstructive sleep apnea. In these cases it can begin as a symptom of the apnea effects but develop over time into a more serious condition. 

The central disorders of hypersomnolence (CDH), as defined by the International Classification of Sleep Disorders  – Third Edition (ICSD-3), include narcolepsy type 1 and type 2,  Kleine-Levin syndrome, insufficient sleep syndrome, idiopathic hypersomnia, and hypersomnia caused by other conditions (either a medical condition, a medication or a substance, or a psychiatric condition). Some examples are listed below, and links are provided for further reading.

Narcolepsy Type 1 (NT1)  

Formerly called narcolepsy with cataplexy, type one is characterized by very low levels (less than 110 pg/mL) of hypocretin 1 (or orexin A) neuropeptide in the cerebrospinal fluid. This shows that narcolepsy is neurological, and in type 1 this results in cataplexy. Cataplexy is a moment of muscle weakness accompanied by full conscious awareness, often triggered by emotions or reactions to external stimuli. About 70 percent of the narcolepsy patient population have type 1, as cataplexy is common among those with narcoleptic symptoms, which is believed to be caused by an autoimmune reaction that destroys the hypothalamic neurons that produce hypocretin 1.

There is increasing evidence that narcolepsy is an autoimmune disorder. This occurs when the body’s immune system turns against healthy tissue or cells. In narcolepsy, it is the immune system that reduces the hypocretin 1 in the cerebrospinal fluid, causing cataplexy and other effects on brain function. While the details of these findings are not yet understood, it is believed that environmental and/or genetic factors may play a role in the development of the disorder. 

Narcolepsy Type 2 (NT2)

Formerly called narcolepsy without cataplexy, this form of narcolepsy does not involve the moments of muscle loss that characterize type 1. As a result, hypocretin 1 levels remain normal or close to normal (some experience a slight decrease), but the symptom of sleepiness remains persistent. Narcolepsy is tested using tools such as the multiple sleep latency test (MSLT), polysomnography, and assessment of sleep architecture. Treatment for narcolepsy may include lifestyle changes such as scheduled naps and exercises, good hygiene, and in some cases, medication. Some medications used for narcolepsy include modafinil, methylphenidate, sodium oxybate, pitolisant, armodafinil, venlafaxine, and antidepressants. 

Kleine-Levin Syndrome (KLS)

Klein-Levin syndrome is a rare condition that usually begins during adolescence, causing episodes of severe sleepiness that last from several days to several weeks. These episodes are recurrent, occurring at least once annually with normal sleep between the episodes. Some patients will also experience hyperphagia (increased hunger/cravings), hypersexuality, and other symptoms during or following the episodes.  Kleine-Levin syndrome is usually diagnosed after ruling out other conditions. Diagnostic approaches include magnetic resonance imaging (MRI), CT scans, and polysomnography. Treatment of Kleine-Levin syndrome mostly occurs during the episodes, and may include the temporary use of modafinil, methylphenidate, and in some cases, amphetamines. 

Insufficient Sleep Syndrome (ISS)

Unlike narcolepsy and Kleine-Levin syndrome, insufficient sleep syndrome is behaviorally induced, often in adolescents and young adults It is estimated that 10-11 percent of the general population experience insufficient sleep symptoms. In addition to sleepiness and fatigue, symptoms can include falling asleep during the day, physical effects on appearance (dark beneath eyes, etc.), and slowed cognition or physical abilities. Routine tasks can become more difficult. Patients may be more prone to accidents or misjudging spatial relationships. And the need for sleep will increase over time. Treatment for insufficient sleep syndrome begins with longer sleep hours. While it may be easy to assume that ISS is easier to treat than other forms of hypersomnolence, the behavioral patterns responsible for the syndrome can be habitual or even compulsive, the result of a complex relationship between more than one contributive factor. 

Hypersomnia due to a medication or substance

Hypersomnia can result from  many other conditions, including behavioral causes. This type of hypersomnia is more prevalent than others, and can be very difficult to treat when chemical dependency issues are involved. Hypersomnolence from sedatives is more common in older people and those with multiple medical conditions, while withdrawal from stimulants or other narcotics is more common among younger populations. The results of these substances tend to present as excessive sleep, excessive daytime sleepiness, or reduced activity. Treatment will vary depending on the nature of the hypersomnia and its cause. 

Hypersomnia due to a medical disorder

Hypersomnia may also be caused by other disorders such as Parkinson’s disease, endocrine disorders, or sleep-related breathing disorders such as sleep apnea. Symptoms are the same for other hypersomnias, consisting mostly of excessive sleepiness, either during the daytime or at night as well. Some patients also experience periods of unrefreshing sleep, sleep hallucinations, or sleep-related movements. For this form of hypersomnia, the multiple sleep latency test (MSLT) is used as a diagnostic tool, as well as general observations and polysomnography. Treatment may include modafinil, methylphenidate, dextroamphetamine, or amphetamine. 

Hypersomnia associated with a psychiatric disorder

Often developing in patients aged 20-50 years, hypersomnia from a psychiatric condition occurs when excessive sleepiness is a symptom of the disorder. Some common disorders that can cause hypersomnia include major depressive disorder (MDD), bipolar disorder, and seasonal affective disorder. Like other forms of hypersomnia, this form results in excessive nocturnal or daytime sleepiness, or generally poor-quality, nonrestorative sleep experiences. Other results can include loss of concentration, weight loss, or weight gain, depending on how the underlying psychiatric condition manifests. Treatment for psychiatric-based hypersomnia may include adjustment of the medication already prescribed, further evaluation by a psychiatrist, or standard hypersomnia medications such as modafinil, bupropion, or antidepressants. 

Idiopathic Hypersomnia

When hypersomnia occurs without an underlying cause or condition, it is referred to as idiopathic hypersomnia. Often present in patients aged between 16 and 21 years, idiopathic hypersomnia often includes severe daytime sleepiness, unwanted napping, and/or difficulty waking or rising after sleep. Some patients also experience sleep inertia, which is a period of impaired senses or movement upon waking. Idiopathic hypersomnia is tested and treated in the same manner as other forms of hypersomnia, though without consideration for other related conditions. In some cases, sleep logs and actigraphy are used as supplements to polysomnography. 


Sleep Apnea and Hypersomnia

When it comes to common symptoms among sleep disorders, differential diagnosis is often the key to proper identification and treatment, especially with symptoms as common as hypersomnolence. For example, in patients with obstructive sleep apnea (OSA), cataplexy should be actively observed in order to exclude the presence of narcolepsy type 1. OSA occurs frequently in narcolepsy and in some cases can delay diagnosis or interfere with proper treatment. Oftentimes the use of PAP therapy will treat multiple conditions simultaneously, greatly improving sleep and quality of life for the patient, but does not normally improve the excessive sleepiness of idiopathic hypersomnia, insufficient sleep syndrome, or narcoleptic conditions. When PAP therapy reduces sleep apnea events but excessive daytime sleepiness persists, it is often necessary to seek other causes for the symptoms. While hypersomnia can have many causes, sleep apnea is often a contributing factor, and this distinction can mean the difference between successful treatment and persistent symptoms. 


Sources –

Multidisciplinary Digital Publishing Institute (MDPI) –

National Institute of Neurological Disorders and Stroke –

National Organization for Rare Disorders (NORD) –

Neurology MedLink –

Sleep Medicine –