Periodic limb movements in sleep (PLMS) Shang Li, Department of Neurology, Shanghai Deji Hospital PLMS was once called nocturnal myoclonus (NM), but its episodes last longer than true myoclonus. PLMS mainly appears during light sleep, especially during N1 and N2 sleep, and manifests as sudden toe- or ankle-dominated, repetitive and fixed form dorsiflexion movements in a form similar to Babinski’s sign. In severe cases, it may be accompanied by flexion of the knee and hip, and may occasionally involve the upper extremity. The PSG can detect recurrent limb movements, as well as disturbances in sleep architecture, increased awakenings during sleep, and other types of sleep disorders. The diagnosis is established if there are more than 4 episodes of PLMS during sleep. If PLMS leads to insomnia or excessive daytime sleepiness, it is called periodic limb movement disorder (PLMD). Its severity is measured by the PLMS index (the number of episodes per hour of sleep, or PLMS index, PLMI). Mild PLMD is defined as 5 ≤ PLMI < 25; moderate PLMD is defined as 25 ≤ PLMI < 50; and severe PLMD is defined as more than 50 or more than 25 episodes per hour with awakening episodes. PLMS is both idiopathic and secondary, and can be seen at any age, with a population prevalence of about 6%. PLMD can be triggered by tricyclic antidepressants, 5-hydroxytryptamine blockers, monoamine oxidase inhibitors, and various antiepileptic drugs. The pathogenesis of the disease is unclear and may involve vascular, systemic, peripheral and central neurological factors. It has been speculated that it may be related to a reticular origin. Patients with spinal cord paralysis and progressive hypospadias due to thoracic spinal cord injury can have a combination of PLMS, suggesting that the disease can also originate in the spinal cord. Both PLMS and PLMD can be misdiagnosed as epileptic motor seizures, which can occur simultaneously during waking hours and be accompanied by epileptic EEG discharges during seizures or interictal periods. Further differentiation can be made with the help of PSG or VPSG. In mild cases, no treatment is required, and non-pharmacologic and pharmacologic treatments can be considered when symptoms are significant. The former focuses on good sleep hygiene and avoidance of PLMS triggers and aggravating factors. Pharmacological treatment mainly involves the application of dopaminergic drugs such as levodopa/Carbidopa, the precursor substance of dopamine, which are preferred to increase the synthesis of dopamine by increasing levodopa in the brain. Dopamine receptor agonists such as Ropinirole, Pramipexole, Pergolide, etc. can also be applied. Dopamine receptor agonists such as bromocriptine also have some efficacy. Opioid agents can be tried in case of poor response to dopaminergic drugs. Benzodiazepines such as clonazepam have been reported to reduce the number of nocturnal awakenings and improve sleep quality in patients with PLMD, and can be used as appropriate.