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Periodic limb movement disorder (PLMD)

Periodic limb movement disorder (PLMD) is a sleep disorder characterised by rhythmic movements of the limbs during sleep. The movements typically involve the legs, but upper extremity movements may also occur. Movements occur periodically throughout the night and can fluctuate in severity from one night to the next. They tend to cluster in episodes that last anywhere from a few minutes to several hours. In contrast, the brief spasms called hypnic myoclonia or hypnic jerks that we often experience initially while trying to fall asleep are so common as to be regarded as normal.

What causes PLMD?

The cause of primary PLMD is unknown. However, secondary PLMD may occur due to a variety of medical problems including diabetes, Parkinson's disease and narcolepsy.

PLMD may be made worse by some medicines including antidepressants, antipsychotics, and antihistamines.

What are the symptoms of PLMD?

Symptoms of PLMD are usually leg movements with the extension of the big toe in combination with a partial flexing of the ankle, knee or hip. Movement of the legs is more typical than movement of the arms. It can often cause a partial or full brief awakening, resulting in fragmented sleep. Patients are frequently unaware of these movements.

How is PLMD diagnosed?

A sleep partner may observe the occurrence of periodic limb movements, which often affect the partner before the patient knows of his or her behaviour. In other cases, the diagnosis is made through an overnight polysomnogram (a test that records sleep and the bioelectrical signals coming from the body during sleep). This test is often used to assess the cause of daytime sleepiness or recurrent awakenings from sleep. Your blood may be tested for its iron, folic acid, vitamin B12 and magnesium levels, and to assess thyroid function.

How is PLMD treated?

Generally, there are several classes of medicines that are used to treat PLMD. These include the Parkinson's disease drugs, anticonvulsant medications, benzodiazepines, and narcotic drugs. Medical treatment of PLMD often significantly reduces the symptoms of these disorders. 

There is no cure for PLMD and medical treatment must be continued to provide relief.

Are there substances that should be avoided?

Caffeine often intensifies PLMD symptoms. Products containing caffeine such as chocolate, coffee, tea and certain soft drinks should be reduced or avoided. Also some antidepressants can worsen PLMD.

Hypnic jerk

Hypnic jerk is another type of involuntary limb movement during sleep which may be experienced. This muscle contraction is also known as hypnic myoclonia, nocturnal myoclonus or sleep jerks. These hypnic jerks may disturb the sleep of a partner, but are common and are not usually a cause for concern.

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WebMD Medical Reference

Medically Reviewed by Dr Rob Hicks on November 10, 2014

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