Thread: Sleep Paralysis- Brutally long and extensive collection of scientific articles with citations.

Sleep paralysis


Contributors

Fabio Pizza MD, author. Dr. Pizza of the University of Bologna in Bologna, Italy, has no relevant financial relationships to disclose.



Federica Provini MD, author. Dr. Provini of the University of Bologna in Bologna, Italy, has no relevant financial relationships to disclose.



Antonio Culebras MD, editor. Dr. Culebras of Upstate Medical University, SUNY, and the Sleep Disorders Center at Community General Hospital has no relevant financial relationships to disclose.



Publication dates

Originally released February 13, 1995; last updated July 24, 2011; expires July 24, 2014




***Key points
• Sleep paralysis is a REM sleep parasomnia characterized by an inability to perform voluntary movements associated with marked anxiety and occurs either at sleep onset (hypnagogic form) or on awakening (hypnopompic form).

• Sleep paralysis attacks last some minutes, do not involve respiratory and ocular muscles, are fully reversible, and often are accompanied by terrifying dream images.

• Sleep paralysis may form part of the narcoleptic tetrad, but isolated sleep paralysis occurs independently from narcolepsy, sometimes in a familial form.

• Sleep paralysis is polysomnographically characterized by the presence of mixed REM-like and wake EEG or EMG features.
***


Historical note and nomenclature
Sleep paralysis was first described in 1876 by Mitchell, who termed it "night palsy" (Mitchell 1876); the term "sleep paralysis" was introduced by Wilson in 1928. Earlier descriptions are, however, found in the medical literature, such as the one by the Dutch physician Isbrand van Diemerbroeck in 1664 (Kompanje 2008). Other names in English used to describe sleep paralysis include "nocturnal paralysis," "cataplexy of awakening," "hypnagogic and hypnopompic paralysis," and "predormital and postdormital paralysis"; in French it has been termed cataplexie du reveil. Furthermore, "Old Hag" in Canada, kanashibari in Japan, "ghost oppression" in Hong Kong Chinese (Wing et al 1994), and ogun oru in Nigerians (Aina and Famuyiwa 2007) are colloquial terms employed by patients and reflect popular credence of sleep paralysis as witchcraft possession and paranormal experiences, very relevant to the issue of transcultural psychiatry (Gangdev 2006; Jacobson 2009; Jimenez-Genchi et al 2009).

Adie and Wilson, in the 1920s, noted that sleep paralysis occurs frequently in narcoleptic patients. Sleep paralysis is included in the "narcoleptic tetrad" together with sleep attacks, cataplexy, and hypnagogic hallucinations. Sleep paralysis may also occur in otherwise normal persons, a condition called "isolated recurrent sleep paralysis." The familial occurrence of isolated sleep paralysis is called "familial sleep paralysis." Isolated recurrent sleep paralysis is classified within the parasomnias usually associated with REM sleep in the current International Classification of Sleep Disorders (American Sleep Disorders Association 2005).




Clinical manifestations
Sleep paralysis is characterized by a brief period of inability to perform voluntary movements occurring at sleep onset (hypnagogic or predormital form) or when awakening, either during the night or in the morning (hypnopompic or postdormital form). Isolated sleep paralysis frequently occurs when awakening (in 64% of patients) (Ohaeri et al 2004), whereas in narcolepsy and familial sleep paralysis, the episodes are more frequent at sleep onset. Spontaneous sleep paralysis episodes showed a skewed distribution over the night, with one quarter of episodes occurring within 1 hour of bedtime, although episodes were reported throughout the night with a minor mode around the time of normal waking (Girard and Cheyne 2006). Typically during sleep paralysis, patients are powerless to move the head, trunk, and limbs as well as to speak and even open the eyes, although ocular and respiratory movements are intact. Sometimes, however, patients feel unable to breathe deeply and have a feeling of suffocation. Usually during sleep paralysis, the patient is fully awake or half awake, the sensorium is clear, awareness of surroundings and self is fairly well-preserved, and patients are able to recall the sleep paralysis afterward. During sleep paralysis, patients usually engage in a mental struggle to cry out and to move, yet they appear to be in deep sleep or dreaming. Sleep paralysis is transient, usually lasting only 1 to several minutes (average duration of episodes 4 minutes) (Ohaeri et al 2004), and disappears either spontaneously or on external stimulation, especially by simple touch or movement induced by another person. Some patients note that repeated efforts to move the body or make vigorous eye movements may help to abort a paralytic episode. Patients may sometimes relapse into sleep paralysis if they remain supine; indeed, sleep paralysis has been shown to occur predominantly with the patient sleeping in the supine position (Dahmen and Kasten 2001), and both body position and timing of the sleep paralysis episodes were found to affect incidence and, to a lesser extent, quality of the sleep paralysis experience (Cheyne 2002). Patients may also fail to establish the boundaries between real experience and dream mentation during the paralysis, suggesting a dissociated state of mind between wakefulness and REM sleep (Terzaghi et al 2012).

Once ended, sleep paralysis usually leaves no sequelae. Neurologic examination is normal. On rare occasions, some weakness or numbness in the extremities remains for a few minutes. Many episodes of sleep paralysis, especially the first to take place in a patient's life, cause extreme anxiety associated with fear of dying during the episode. This anxiety is greatly intensified by terrifying dreamlike images or hallucinations (hypnagogic or hypnopompic hallucinations) that often accompany sleep paralysis, and whose basic forms and patterns are independent from prior experiences and rather the expression of intrinsic REM processes (Cheyne 2005). In a single case report, exploding head syndrome was followed by sleep paralysis as a unique aura of migraine headache (Evans 2006).

Sleep paralysis occurs with different frequencies in different patients. Frequency of sleep paralysis varies even in a single patient. According to Ohaeri and colleagues, in 110 Nigerians, mean isolated sleep paralysis frequency in the lifetime, past year, and past month was respectively 6.7, 2.02, and 0.5 (Ohaeri et al 2004). Using International Classification of Sleep Disorders criteria, 2.7% had sleep paralysis at least once per week, 18.2% once per month, and 75.5% less than once per month. In many narcoleptic patients, sleep paralysis occurs every night in some periods of life but becomes much less frequent in other times of life. In general, patients who frequently experience sleep paralysis learn that the episodes are brief, benign, and have no significant aftermath. When sleep paralysis occurs every night in bed, as is sometimes found in narcoleptic patients, some learn to sleep sitting upright in order to avoid it.

The current International Classification of Sleep Disorders (American Sleep Disorders Association 2005) cites the following:



Table 1. Diagnostic Criteria for Recurrent Isolated Sleep Paralysis



The patient complains of:

(A) Inability to move the trunk and all limbs at sleep onset or on waking from sleep.

(B) Each episode lasts seconds to a few minutes.

(C) The sleep disturbance is not better explained by another sleep disorder (particularly narcolepsy), a medical or neurologic disorder, mental disorder, medication use, or substance use disorder.



Of note:

Hallucinatory experiences may be present but are not essential to the diagnosis. Polysomnography, if performed, reveals the event to occur in a dissociated state with elements of REM sleep and wakefulness.



It must be kept in mind that sleep paralysis frequently occurs in narcoleptic patients and may occur in patients with other medical diseases or mental disorders, including bipolar affective disorder and schizophrenia with severe disturbance of nocturnal sleep. Isolated recurrent sleep paralysis may be associated with a family history: at least 2 families with recurrent sleep paralysis have been reported and a maternal transmission has been suggested.