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Periodic limb movements in sleep (PLMS) is a disorder characterized by a cyclic pattern of motor phenomena and EEG changes (mostly arousals), both recurring at approximately 20- to 40-s intervals. The periodicity of the PLMS phenomena recalls the physiological EEG arousal rhythm of non-rapid eye movement (NREM) sleep known as the cyclic alternating pattern (CAP). During CAP, arousals and arousal-equivalent features do not appear as isolated events but periodically intrude (phase A) between intervals of background EEG activity (phase B). Though the A phases can be expressed by a variety of EEG patterns, each with a different arousal impact on polygraphic parameters, overall CAP is a sequence of biphasic cycles reflecting a condition of unstable sleep. Twelve middle-aged PLMS subjects complaining of poor sleep were polygraphically compared with 12 age-matched and gender-matched healthy volunteers (controls). With respect to controls, the PLMS recordings showed an enhancement of the more powerful arousals and presented significantly increased amounts of CAP time (+45 min) and CAP rate (+15%). Of all the jerks detected in NREM sleep, 92% occurred in CAP, with the great majority of limb movements (96%) associated with phase A. Ninety-four percent of the nocturnal jerks coupled with phase A started jointly with the onset of the phase or when the latter had already begun. In particular, most of the myoclonic events (67%) occurred in the first 2.5 s of the A phase. The CAP cycles coupled with periodic movements were significantly longer than those without motor events (+6.4 s). Compared to the American Sleep Disorders Association's rules for scoring EEG arousals, the CAP framework offers a more extensive insight into PLMS. In effect, the present study indicates an entrainment of nocturnal myoclonus by means of CAP and sheds light on the complex interactions between arousal mechanisms and motor phenomena during sleep.

Objective To evaluate sleep in children with autistic spectrum disorder (ASD) by means of sleep questionnaires and polysomnography; moreover, to analyze their cyclic alternating pattern (CAP). Methods Thirty-one patients with ASD (28 males, 3 females, aged 3.7–19 years) and age-matched normal controls were included. ASD children were evaluated by a standard sleep questionnaire that consisted of 45 items in a Likert-type scale covering several areas of sleep disorders and by overnight polysomnography in the sleep laboratory after one adaptation night. Results The questionnaire results showed that parents of ASD children reported a high prevalence of disorders of initiating and maintaining sleep, enuresis, repetitive behavior when falling asleep, and daytime sleepiness. Polysomnographically, ASD children showed reduced time in bed, total sleep time, sleep period time and rapid eye movement (REM) latency. ASD subjects had a CAP rate during slow-wave sleep (SWS) lower than normal controls, together with a lower percentage of A1 subtypes. Conclusions ASD children questionnaires showed a higher percentage of disorders of initiating and maintaining sleep than normal controls; this was not completely confirmed by sleep staging. CAP measures showed subtle alterations of NREM sleep which could be detected with an appropriate methodology of analysis. The reduction of A1 subtypes during SWS might play a role in the impairment of cognitive functioning in these subjects.