Sleep paralysis is a common condition with a prevalence of 5-62%. Although most affected people have single or infrequent episodes, sleep paralysis may be recurrent, or occur in association with the narcoleptic syndrome. In a study of 22 subjects with frequent sleep paralysis and also excessive daytime sleepiness, episodes continued for between 5 and 35 years. In contrast to subjects with the narcoleptic syndrome, these patients did not have cataplexy, daytime sleepiness and insomnia were less severe, and there was no HLA DR2(15) or DQ1(6) association. Sleep paralysis was familial in 19 of these subjects. A non-HLA linked genetic factor, in addition to environmental factors, may thus predispose to sleep paralysis.
Seventeen children and young adults with the Prader-Willi syndrome were investigated. Twelve of 17 subjects had excessive daytime sleepiness as determined by their own or parental report, a high Epworth Sleepiness Scale score or a short mean sleep latency. Night sleep disturbances were reported in seven subjects with snoring, mouth-breathing, breath-holding and occasional nocturnal enuresis. Polysomnography showed abnormalities of sleep structure with rapid eye movements without reduction in muscle tone at sleep onset in 12 subjects, and a high respiratory event index with frequent brief apnoeas, particularly in REM sleep, in 16 subjects. Most apnoeas were not accompanied by arousals. Seven subjects, all of whom were obese, were considered to have symptomatic sleep apnoea and were treated with continuous positive airway pressure (CPAP) but this was poorly tolerated in two. Five subjects continued CPAP over a 6-month period resulting in subjective improvement in excessive daytime sleepiness in 3. Excessive daytime sleepiness occurs in approximately two-thirds of subjects with the Prader-Willi syndrome. It is mainly of central origin but obstructive sleep apnoea may increase sleepiness, particularly in obese subjects.
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