Periodic limb movement disorder (PLMD) is unique in that the movements occur during sleep. Most other movement disorders manifest during wakefulness. The condition is remarkably periodic, and the movements may cause poor sleep and subsequent daytime somnolence. PLMD may occur with other sleep disorders and is related to, but not synonymous with, restless legs syndrome (RLS), a less specific condition with sensory features that manifest during wakefulness. The majority of patients with RLS have PLMD, but the reverse is not true. Treatment involves either dopaminergic medication in an attempt to modify activity of the subcortical motor system or, more commonly, sedative medications to allow uninterrupted sleep. Many new agents are proving efficacious for treatment as well.
The etiology of the primary form of periodic limb movement disorder is uncertain. Suprasegmental disinhibition of the descending inhibitory pathways may be a factor. Vetrugno and colleagues report that evidence supports neuronal hyperexcitability with involvement of the central pattern generator for gait as the pathophysiology of periodic limb movement.  This results in decreased dopamine transmission, potentially supporting the use of dopaminergic therapy to treat the condition.
Because the etiology is not clear, treatment is primarily to treat symptoms and does not modify the disease. Studies differ regarding the frequency of polyneuropathy in cases of periodic limb movement disorder. Martinez-Mena and Pastor found that only 1 of 9 patients had signs of neuropathy. 
The secondary forms of periodic limb movement disorder may be due to diabetes mellitus, spinal cord tumor, sleep apnea syndrome, narcolepsy, uremia, or anemia.  Many authors report an association between attention deficit hyperactivity disorder (ADHD) and periodic limb movement disorder. Antidopaminergic, dopaminergic, or tricyclic drug therapy or cessation of treatment with barbiturates or benzodiazepines may initiate the syndrome as well.  Voderholzer and colleagues noted an increased incidence of periodic limb movements during sleep in patients with Gilles de la Tourette syndrome.  However, the authors emphasized that the different responses to pharmacological treatments are evidence against a pathophysiological relationship between periodic limb movement disorder and Gilles de la Tourette syndrome.
Potential risk factors or etiologic factors for secondary periodic limb movement disorder include the following:
Spinal cord injury
The prevalence of periodic leg movements in sleep (PLMS) is estimated to be 4–11% in adults.  PLMS are most frequently a symptom of restless legs syndrome (RLS).They also often occur in narcolepsy, sleep apnea syndrome, and REM sleep behavior disorder. Some patients with otherwise unexplained insomnia or excessive daytime sleepiness exhibit an elevated number of PLMS, a condition defined as periodic limb movement disorder (PLMD).
The idiopathic form of this syndrome may be chronic. Relapses and remissions may occur, but treatment does not appear to modify the disease.
The secondary form of this syndrome may cease with treatment of the underlying cause.
Picchietti and colleagues suggested that the sleep disruption in periodic limb movement disorder could contribute to the inattention and hyperactivity of some children who have ADHD. 
Informing the bed partner of the condition is important so that potentially negative physical contact may be explained on a neurological (rather than an intentional) basis.
For excellent patient education resources, visit eMedicineHealth's Sleep Disorders Center. Also, see eMedicineHealth's patient education articles Periodic Limb Movement Disorder, Restless Legs Syndrome, Sleep Disorders in Women, and Sleep Disorders and Aging.
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