Periodic limb movements
Oct. 16, 2023
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In this article, the author details the clinical and laboratory features of sleep paralysis, an intriguing REM sleep-related parasomnia found in a relevant number of otherwise normal subjects and associated but not coincidental with narcolepsy-cataplexy. Sleep paralysis may be familial and is thought to represent a disorder of REM sleep, whereby muscle atonia typical of REM sleep is concomitant with a wakeful conscious experience. The hallucinations of sleep paralysis seem to revolve around a core experience of “sensed presence” consistent with the hypothesis of REM sleep initiation of a threat-activated vigilance system.
• Sleep paralysis is a REM sleep parasomnia characterized by an inability to perform voluntary movements associated with marked anxiety that occurs either at sleep onset (hypnagogic form) or on awakening (hypnopompic form).
• Sleep paralysis attacks last a few minutes, do not involve respiratory and ocular muscles, are fully reversible, and often are accompanied by terrifying hallucinatory phenomena.
• Sleep paralysis may form part of the narcoleptic tetrad, but isolated sleep paralysis occurs independently of narcolepsy, sometimes in a familial form.
Sleep paralysis was first described in 1876 by Mitchell, who termed it "night palsy" (26); the term "sleep paralysis" was introduced by Wilson in 1928. Earlier descriptions are, however, found in the “modern” medical literature, such as the one by the Dutch physician Isbrand van Diemerbroeck in 1664 (21), as well as in the “ancient” medical literature, such as that from the Persian Akhawayni in his Hidayat al-muta’allemin fi al-tibb (Learner’s guide to medicine) compiled in the 10th century and others from the ancient Chinese and Greek culture (13). Literary descriptions of sleep paralysis can also be found in “The Horla” by Guy De Maupassant, in the novel Moby Dick by Herman Melville (25), in The Brothers Karamazov by Fyodor Dostoyevsky (37), and in Nikolai Gogol's tale "The Portrait" (01). 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 réveil. Furthermore, "Old Hag" in Canada, kanashibari in Japan, "ghost oppression" in Hong Kong Chinese, and ogun oru in Nigerian 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 (08). Moreover, the endorsement of a supernatural causal explanation of sleep paralysis is highly influenced by cultural and educational background, which can profoundly shape certain aspects of the experience during the episodes (18).
Adie and Wilson, in the 1920s, noted that sleep paralysis occurs frequently in patients with narcolepsy. When sleep paralysis occurs independently of narcolepsy and other medical conditions, it is termed “isolated” sleep paralysis. The more specific diagnostic syndrome of “recurrent isolated sleep paralysis,” classified in the current International Classification of Sleep Disorders within REM related parasomnias (02), is defined when sleep paralysis causes clinically significant distress including bedtime anxiety or fear of sleep.
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