1. Nosological classification, definitions, and epidemiology

During sleep, several motor manifestations occur as physiological (i.e., fragmentary myoclonus during sleep, sleep starts, gross body movements) or pathological motor phenomena. Sleep-related movement disorders (SRMD) are characterized typically by simple, often stereotypical, involuntary movements and can associate with disturbances (e.g. insomnia) and daytime symptoms. SRMD can be primary or secondary to a neurological or general medical condition, where they can be frequent comorbidities. Their clinical phenomenology is broad, and disorders are usually distinguished according to the body part(s) and the type of motor activity involved. Their prevalence is significant in general population, thus, SRMD are of high clinical relevance for the sleep specialist. According to the American Academy of Sleep Medicine (International Classification of Sleep Disorders third ed., ICSD-3), SRMD include restless leg syndrome, periodic limb movement disorder (PLMD), sleep-related leg cramps, sleep-related bruxism, sleep-related rhythmic movement disorder, benign sleep myoclonus of infancy, propriospinal myoclonus at sleep onset, and sleep-related movement disorder either unspecified, due to drug or substance intake, or a medical condition.