Chapter 10

Motor control in sleep is as complex as in wakefulness but clearly different. Sleep is considered a state of relative mental and physical inactivity; sleep, however, is not simply a state of passivity. We see both negative and positive phenomena during sleep. Furthermore, the status immediately before sleep onset (predormitum) and just before sleep offset in the morning (postdormitum) are distinct from sleep and wakefulness proper with different motor behavior (e.g., propriospinal myoclonus and hypnic jerks in predormitum and sleep inertia in postdormitum). Many diurnal abnormal movements continue in sleep but to a lesser degree than in wakefulness, whereas new adventitious movements may be triggered by sleep, causing the paradox of a sleeping brain with an active body. Modern technology using video-polysomnographic recordings and neuroimaging (positron emission tomography, single-photon emission computed tomography, and other functional magnetic resonance imaging displays) have opened up a new world of nocturnal events encompassing both physiological and pathological motor manifestations, shedding light on the pathophysiology of many sleep-related movement disorders.

The second edition of the International Classification of Sleep Disorders published in 2005 included a separate section devoted to sleep-related movement disorders. This category includes restless legs syndrome, periodic limb movements in sleep and periodic limb movement disorder, sleep-related leg cramps, sleep-related bruxism, sleep-related rhythmical movement disorders, and other sleep-related movement disorders caused by a known physiological condition or substance abuse and those not caused by a substance or known physiological condition (e.g., other psychiatric or behavioral sleep-related movement disorders). Most of the nosological entities characterized by prominent motor abnormalities are, however, included in the category of parasomnias (e.g., undesirable motor events and behavior occurring during sleep that do not necessarily disturb sleep architecture and that are not caused by abnormalities intrinsic to basic sleep mechanisms). Parasomnias include disorders of arousals (e.g., confusional arousals, sleepwalking, sleep terrors arising out of non–rapid eye movement [NREM] sleep), those associated with rapid eye movement (REM) sleep (e.g., REM sleep behavior disorder, parasomnia overlap disorder, status dissociatus, nightmares, and recurrent isolated sleep paralysis), and other parasomnias (e.g., nocturnal dissociative disorder, catathrenia or nocturnal groaning, exploding head syndrome, and sleep-related eating disorders). While we await a deeper understanding of the pathophysiological mechanisms, however, description remains the first step in the knowledge of a phenomenon. Video recordings and polygraphic pictures go a long way in helping clinicians to recognize and characterize the various movement abnormalities encountered in the everyday practice of sleep medicine. Therefore an atlas showing characteristic polysomnographic (PSG) features of different motor disorders arising during sleep provides a good guide in the interpretation of the tracings and helps technicians and physicians recognize patterns useful in the differential diagnosis. Figures 10.1 to 10.12 provide examples of PSG tracings and a brief clinical description for clinical-physiological correlation derived from the following motor disorders emerging during sleep: sleep terror (see Fig. 10.1), status dissociatus (see Fig. 10.2), propriospinal myoclonus at sleep onset (see Fig. 10.3), faciomandibular myoclonus (see Fig. 10.4), sleep-related eating disorder (see Fig. 10.5), bruxism (see Fig. 10.6), bruxism with catathrenia (see Fig. 10.7), hypnagogic foot tremor (see Fig. 10.8), alternating leg muscle activation (see Fig. 10.9), excessive fragmentary myoclonus (see Fig. 10.10), and confusional arousal (see Figs. 10.11 and 10 12).