Periodic Limb Movement Disorder (PLMD) is characterized by repetitive limb movements that occur while sleeping or lying awake (mostly the lower legs), involving brief muscle twitches, and an upward dorsi-flexion of the foot, knee or hip. It is considered abnormal where there are more than 5 or more involuntary movements per hour of sleep with each limb movement lasting 0.5 to 5 seconds in duration. Although the patient is typically not aware of these limb movements, the patient’s quality of sleep is often compromised and their bed partner might recognize them. These frequent limb movements can disrupt your sleep and may cause you or your bed partner to have insomnia, restless sleep, or excessive daytime sleepiness. Although periodic limb movements during sleep (PLMS) are typically seen in patients with restless legs syndrome (RLS), patients with periodic limb movement disorder (PLMD) by definition do not have RLS symptoms. The cause of PLMD remains unclear, but it appears have some similarities with RLS. PLMD also appears to be a dopamine responsive disorder. That is, it is typically improved following treatment with dopaminergic agonists. Moreover, as with RLS, lower levels of iron in the brain may make symptoms worse, as well as some anti-nausea medications, antidepressants, and lithium.
You may or may not be aware of your symptoms, which makes it harder for you to know if leg movements may be present during sleep. However, there are some symptoms that may make you suspect this disorder, or symptoms that a bed partner may have mentioned to you.
- Do you have repetitive and intermittent limb movements while asleep?
- Are your bed sheets a mess or untidy in the morning or do you feel you have had restless sleep at night?
- Do you feel fatigued or sleepy even though you had a full night sleep?
PLMD may be found in children and adults. Its occurrence increases with age and is particularly common in the elderly, affecting 35% of people aged 65 and older. Periodic limb movements in sleep may also be caused by other sleep disorders such as RLS or obstructive sleep apnea.
Like any sleep disorder, PLMD may affect your ability to maintain adequate restorative sleep and cause you to experience excessive daytime sleepiness. When you suffer from a sleep loss, you are more prone to fatigue, increased illness, impaired task performance, decreased memory, short attention span, altered mood, depression or anxiety. It is important to consult a qualified sleep medicine physician, especially if the symptoms adversely affect your quality of sleep, daytime functioning, or worsen with age.
It may be helpful to keep a sleep diary prior to meeting your physician to record your sleep quality and quantity as well as when your symptoms occur and their severity. You most likely will undergo an overnight sleep study (polysomnogram) to determine if periodic limb movements are occurring during sleep. Your physician will also determine if other health conditions or medications that may be contributing to the symptoms.
If another underlying disorder such as obstructive sleep apnea causes your symptoms, your physician will address it so as to decrease the severity of your symptoms. If necessary, your doctor may prescribe a medication that is also used to treat RLS (see Treatment of RLS). Treatment is administered according to the severity of the symptoms, the level of relief experienced with the medication and any potential side effects experienced by the patient.