Medically reviewed by
Dacelin St Martin, MD
Triple board-certified in Sleep Medicine,
Internal Medicine, and Pediatrics.
Sleep is an essential biological function, playing a significant role in the recovery, energy conservation, and survival of an individual.
It plays a vital role in normal neural development, learning, memory, emotional regulation, cardiovascular and metabolic function, and cellular toxin removal.
Sleep has been classified by the American Academy of Sleep Medicine (AASM) to differentiate disorders and facilitate the understanding of symptoms, etiology, and pathophysiology that allows for effective treatment.
The ICSD-2 lists the 81 disorders major sleep disorders in 8 major categories:
- The insomnias
- The sleep-related breathing disorders
- The hypersomnias of central origin
- The circadian rhythm sleep disorders
- The parasomnias
- The sleep-related movement disorders
- Isolated symptoms, apparently normal variants, and unresolved issues 
When talking about hypersomnia, which is explained as daytime sleepiness or the inability to stay alert and awake during the significant waking occurrences of the day, the cause of its symptoms lies elsewhere than in disturbed sleep or a misaligned circadian rhythm.
Kleine–Levin syndrome (KLS) is one of several disorders of hypersomnia that fall into the category of central disorders of hypersomnia, with others including narcolepsy types 1 and 2 and idiopathic hypersomnia.
The term “Kleine-Levin syndrome” was first described by Kleine in 1925 and later elaborated by Levin in 1936, but Critchley and Hoffman further elaborated its definition in 1942.
In their work “The Syndrome of Periodic Somnolence and Morbid Hunger,” they have described the case of two men who developed hypersomnia and hyperphagia (extreme hunger), with one of the two patients developing symptoms six months after vaccination.
Furthermore, the authors stated that potential mechanisms could involve a form of mild inflammation of the brain, known as encephalitis, affecting the hypothalamus and the frontal lobes.
The American Academy of Sleep Medicine described KLS as a rare disease characterized by recurrent episodes of hypersomnia and behavioral or cognitive disturbances, compulsive eating behavior, and hypersexuality to various degrees. 
In addition to hypersomnia, at least one of the following symptoms must be present:
- Cognitive or mood disturbances
- Excessive hunger with compulsive eating
- Abnormal behavior, such as irritability, aggression, or personality changes
- Since it is a rare disease, its estimated prevalence is between one to five cases per million population
- The disease predominantly affects adolescent males
- Worldwide, there are patients with primary KLS, but the disorder is more prevalent among Ashkenazi Jews
- The disease predominantly affects adolescent males
- Studies show that the median age of onset of KLS is 16 years
- Approximately 80 percent of cases reported belonged to the second decade of life within a range of 4 to 82 years.
- Patients with typical symptoms were of the age group >35 years
- Whereas the patient with childhood-onset, i.e., <12 years, was associated with more frequent episodes.
Currently, the etiology of KLS is unknown. Although theories were explained, they were primarily focused on genetic and immune-mediated causes.
Genetic factors – the preponderance of cases in the Ashkenazi Jewish population was the basis of the genetic hypothesis, although, to date, no specific genes have been identified. There’s an estimated 1% chance of getting KLS from a first-degree relative of a patient with KLS.
Infectious & Immune-Mediated Theories
According to studies conducted by Billiard M et al., it was stated that “Focal viral encephalitis or postinfectious autoimmune encephalitis affecting specific areas of the brain (i.e., thalamus-hypothalamus, frontal and temporal lobes) would be consistent with the nature of the disease.”
KLS-like symptoms are also associated with tumors of the hypothalamus, frontal lobe, and temporal lobe, which control sleep, perception, mood, and impulse control.
Infections reported in association with KLS include:
- Epstein-Barr virus
- Herpes zoster
- Influenza A and B
- Adenovirus, enterovirus
- Salmonella typhi
Precipitating factors – apart from genetic and immune factors, include:
- Alcohol ingestion
- Sleep deprivation
- Unusual stress
- Physical exertion
The onset of KLS has also been reported after vaccinations, including:
The key share of clinical presentation of KLS includes recurrent hypersomnia, which means recurrent episodes of excessive daytime sleepiness lasting for 2 days to 4 weeks. The reoccurrence of these episodes is at least once per year.
Apart from the recurrent hypersomnia, the clinical features of Kleine Levin syndrome also include:
– Cognitive abnormalities such as:
- Derealisation: sensations of unreality
– Abnormal behavior such as:
- Change in eating orders
The diagnostic procedures for KLS include:
1) Electroencephalography (EEG): the EEG in KLS shows a generalized slowing in up to 70% of cases during episodes
2) Polysomnography (PSG):
- When done at the beginning of an episode, a decrease in slow-wave sleep is observed
- Whereas when performed towards the end of an episode, a decrease in rapid eye movement (REM) sleep may be observed
3) Single-Photon Emission Computed Tomography (SPECT):
- SPECT is a diagnostic tool used to show blood flow through organs and tissues
- During SPECT, a positive finding may include inadequate delivery of oxygen, known as hypoperfusion, to the brain, namely the thalamus, hypothalamus, temporal lobes, orbitofrontal and parasagittal frontal lobes, and, less commonly, the basal ganglia and occipital regions
- Hypoperfusion may persist in the mesial temporal lobe, frontal lobe, and basal ganglia during asymptomatic periods
4) Neuropsychological Testing:
- This test can help identify the impairment in working memory during episodes
- Persistent deficits in immediate and delayed, verbal and visual recall in some individuals
According to a review conducted by Mighlis et al., the treatment procedure of KLS primarily comprises 2 phases:
Supportive/ Education Phase
The supportive phase includes:
- Postponing or adjusting school and work activities
- Not allowing the patient to wander unattended or to operate a car or heavy machinery
- Monitoring the symptoms of depression or anxiety
- Maintaining consistent sleep-wake schedules, avoiding alcohol and sick contacts
- Consider amantadine if a patient presents in the early stages of an episode
- Consider modafinil for excessive daytime sleepiness in the early symptomatic period
- Consider the short-term course of an antidepressant, mood stabilizer, anxiolytic or antipsychotic for psychiatric symptoms
Consistent restorative sleep is critical for good health and overall quality of life. So for maintaining physical and mental well-being, it is vital to address the etiology of the sleep disorders and have adequate knowledge regarding the same.
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