Abstract
Type 1 narcolepsy is a central hypersomnia due to the loss of hypocretin-producing neurons and characterized by cataplexy, excessive daytime sleepiness, sleep paralysis, hypnagogic hallucinations and disturbed nocturnal sleep. In children, close to the disease onset, type 1 narcolepsy has peculiar clinical features with severe cataplexy and a complex admixture of movement disorders occurring while awake. Motor dyscontrol during sleep has never been systematically investigated. Suspecting that abnormal motor control might affect also sleep, we systematically analysed motor events recorded by means of video polysomnography in 40 children with type 1 narcolepsy (20 females; mean age 11.8 ± 2.6 years) and compared these data with those recorded in 22 age- and sex-matched healthy controls. Motor events were classified as elementary movements, if brief and non-purposeful and complex behaviours, if simulating purposeful behaviours. Complex behaviours occurring during REM sleep were further classified as 'classically-defined' and 'pantomime-like' REM sleep behaviour disorder episodes, based on their duration and on their pattern (i.e. brief and vivid-energetic in the first case, longer and with subcontinuous gesturing mimicking daily life activity in the second case). Elementary movements emerging either from non-REM or REM sleep were present in both groups, even if those emerging from REM sleep were more numerous in the group of patients. Conversely, complex behaviours could be detected only in children with type 1 narcolepsy and were observed in 13 patients, with six having 'classically-defined' REM sleep behaviour disorder episodes and seven having 'pantomime-like' REM sleep behaviour disorder episodes. Complex behaviours during REM sleep tended to recur in a stereotyped fashion for several times during the night, up to be almost continuous. Patients displaying a more severe motor dyscontrol during REM sleep had also more severe motor disorder during daytime (i.e. status cataplecticus) and more complaints of disrupted nocturnal sleep and of excessive daytime sleepiness. The neurophysiological hallmark of this severe motor dyscontrol during REM sleep was a decreased atonia index. The present study reports for the first time the occurrence of a severe and peculiar motor disorder during REM sleep in paediatric type 1 narcolepsy and confirms the presence of a severe motor dyscontrol in these patients, emerging not only from wakefulness (i.e. status cataplecticus), but also from sleep (i.e. complex behaviours during REM sleep). This is probably related to the acute imbalance of the hypocretinergic system, which physiologically acts by promoting movements during wakefulness and suppressing them during sleep.
Highlights
Type 1 narcolepsy (NT1) is a central disorder of hypersomnolence (ICSD third ed.), characterized by loss of boundaries between sleep and wake, with frequent state transitions and intrusions of REM sleep into the other ongoing states of being (Broughton et al, 1986; Dauvilliers et al, 2007a; Diniz Behn et al, 2010), due to a deficiency of hypothalamic hypocretin 1 signalling (de Lecea et al, 1998; Sakurai et al, 1998), of a likely autoimmune aetiology (Partinen et al, 2014)
Neurophysiological investigation of sleep in narcolepsy has grown (Mukai et al, 2003; Dauvilliers et al, 2007b; Ferri et al, 2008a, 2009; Roth et al, 2013; Sorensen et al, 2013; Jensen et al, 2014; Christensen et al, 2015; Pizza et al, 2015), but so far it has mainly focused on sleep dynamics, omitting the phenomenological descriptions of movement disorders occurring during sleep
Analysing motor episodes occurring during non-REM sleep stage 1 (NREM) sleep, we show that both NT1 and healthy control subjects present with the same probability of displaying elementary movements, while complex behaviours suggesting NREM parasomnias, except for a single NT1 patient, are not frequent
Summary
Type 1 narcolepsy (NT1) is a central disorder of hypersomnolence (ICSD third ed.), characterized by loss of boundaries between sleep and wake, with frequent state transitions and intrusions of REM sleep into the other ongoing states of being (Broughton et al, 1986; Dauvilliers et al, 2007a; Diniz Behn et al, 2010), due to a deficiency of hypothalamic hypocretin 1 (orexin) signalling (de Lecea et al, 1998; Sakurai et al, 1998), of a likely autoimmune aetiology (Partinen et al, 2014) It is a lifelong disorder, arising in childhood (Nevsimalova, 2009; Aran et al, 2010; Luca et al, 2013; Thorpy and Kriger, 2014) and early adulthood (Dauvilliers et al, 2001). Neurophysiological investigation of sleep in narcolepsy has grown (Mukai et al, 2003; Dauvilliers et al, 2007b; Ferri et al, 2008a, 2009; Roth et al, 2013; Sorensen et al, 2013; Jensen et al, 2014; Christensen et al, 2015; Pizza et al, 2015), but so far it has mainly focused on sleep dynamics, omitting the phenomenological descriptions of movement disorders occurring during sleep
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