Narcolepsy is a sleep disorder characterized by excessive daytime sleepiness, unstoppable sleep attacks and various accompanying symptoms. People with narcolepsy experience short episodes of sleep. The person may not be able to resist these sleep attacks.
Narcolepsy, which occurs in approximately 0.02-0.05% of the general population, is more common in men than in women. It usually starts suddenly in the 10s or 20s. The diagnosis is based on history, polysomnography and Multiple Sleep Latency Test (MSLT) findings. Although narcolepsy usually follows a permanent course, symptom severity may decrease as patients adapt to the symptoms.
Clinical Symptoms
The most prominent symptom of this disorder is daytime sleep attacks. After these episodes, which usually last 10-20 minutes, the person may feel rested for a short period of time. These episodes may occur at socially inappropriate times such as chatting, driving or listening to lectures. The frequency and severity of sleep attacks may vary from person to person.
Other symptoms that often accompany excessive daytime sleepiness include cataplexy, sleep paralysis and hypnogogic or hypnopompic hallucinations. Cataplexy is characterized by a transient loss of muscle tone as a result of a sudden emotional reaction. This event develops independently of the sleep episode and usually ends spontaneously within a few minutes. The frequency of cataplexy attacks may vary individually.
Sleep paralysis is the inability to move during falling asleep or waking from sleep. At this time, the individual is consciously aware of his/her surroundings, but cannot use voluntary muscles and the ability to speak is temporarily lost. This can lead to intense anxiety and fear. When the attack is over, the person remembers their experiences clearly.
Another symptom of narcolepsy is hallucinations. These hallucinations, which occur while falling asleep (hypnogogic) or waking up (hypnopompic), may be visual, auditory or tactile. Most of the time, they may have illusory characteristics as they can be confused with real perceptions. Hallucinations can occur at any stage of the disease.
Another common symptom of narcolepsy sleep disorder is poor quality and constant interruption of night sleep. Frequent short awakenings during the night can prevent the patient from feeling rested and can exacerbate daytime symptoms.
The diagnosis of narcolepsy is usually made on the basis of a detailed history taken from the patient himself/herself, his/her family or close relatives and clinical evaluations. According to the International Classification of Sleep Disorders, diagnostic tests such as polysomnography, Multiple Sleep Latency Test (MSLT) and measurement of hypocretin levels in cerebrospinal fluid are required to confirm the diagnosis.
Diagnostic Criteria
In the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) published by the American Psychiatric Association (APA), the diagnostic criteria for narcolepsy are as follows:
A: Recurrent, unsuppressible sleep requirement, sudden falling asleep or napping (short daytime sleep) phases occurring on the same day. These must have occurred at least three times a week in the last three months.
B: Presence of at least one of the following:
1. Episodes of cataplexy, described as (a) or (b), occurring at least several times a month:
a. Sudden brief (seconds or minutes) periods of bilateral loss of normal muscle tension (tone), triggered by laughing or joking, with preservation of consciousness in people with a long-standing illness.
b. Periods of spontaneous grimacing or jaw opening with tongue misplacement or generalized low muscle tension (hypotonia), occurring in the absence of overt emotional triggers in children or people who have been ill for less than six months.
2. Hypocretin deficiency measured using cerebrospinal fluid (CSF) hypocretin-1 immunoreactivity values (less than or equal to one-third of the values obtained in healthy subjects by the same examination, or less than or equal to 110 pg/mL). Low hypocretin-1 in CSF should not have been observed in the context of acute brain injury, inflammation or infection.
3. Polysomnography of nocturnal sleep shows the onset of rapid eye movement sleep (REM) in 15 minutes or less, an average fall asleep time of 8 minutes or less on the multiple falls asleep measure, and a REM phase that occurs in combination with two or more than two falls asleep.
Etiology
The exact causes of narcolepsy are not yet fully understood, but different explanations have been proposed. One of these is based on disturbances in the balance and control mechanisms between sleep and wakefulness.
Another explanation is that there may be a disruption in the functioning of sleep regulatory systems. Sleep is governed by the interaction of both homeostatic and circadian processes. The harmony of these two systems ensures that periods of sleep and wakefulness occur regularly throughout the day. In narcolepsy, it is thought that the functions of one or both of these regulatory systems may be impaired. This may manifest itself in symptoms such as sudden sleep attacks during the day and interrupted nighttime sleep.
It has been determined that the incidence of narcolepsy in first-degree relatives is higher than in the general population. In addition, a study has shown that the likelihood of the disease in individuals with a genetic predisposition varies according to the birth order and the risk is higher especially in the third or later births. Head traumas, cerebrovascular diseases, hemorrhages and infections are among the possible triggers.
There is also some suggestion that a deficiency in the brain of hypocretin, which plays an important role in regulating the sleep-wake cycle and is produced by the hypothalamus, may lead to narcolepsy.
