What is periodic limb movement disorder (PLMD)?

Periodic limb movement disorder (PLMD) is a condition that was formerly called sleep myoclonus or nocturnal myoclonus. It is described as repetitive limb movements that occur during sleep and cause sleep disruption. The limb movements usually involve the lower extremities, consisting of extension of the big toe and flexion of the ankle, the knee, and the hip. In some patients, the limb movements can occur in the upper extremities as well.

The limb movements occur most frequently in light non-REM sleep. The repetitive movements are separated by fairly regular intervals of 5 to 90 seconds. There can be significant night-to-night variability to the frequency of limb movements.

Who gets periodic limb movement disorder (PLMD)?

Many individuals have periodic limb movements in sleep (PLMS). This is observed in about 80% of patients with restless legs syndrome (RLS). PLMS can occur in over 30% of people aged 65 and older and can be asymptomatic. PLMS are very common in patients with narcolepsy and REM behavior disorder, and may be seen in patients with obstructive sleep apnea and during PAP therapy initiation.

True PLMD – the diagnosis of which requires periodic limb movements in sleep that disrupt sleep and are not accounted for by another primary sleep disorder including RLS – is uncommon.

PLMD has been less extensively studied than RLS. The exact prevalence is unknown. It can occur at any age; however, the prevalence does increase with increasing age. Unlike RLS, PLMD does not appear to be related to gender.

As with RLS, some medical conditions are associated with PLMD. These include uremia, diabetes, iron deficiency, OSA, and spinal cord injury.

What causes periodic limb movement disorder (PLMD)?

The exact cause of PLMD is unknown. However, several medications are known to make PLMD worse. These medications include some antidepressants, antihistamines, and some antipsychotics.

What are some of the symptoms of periodic limb movement disorder (PLMD)?

Most patients are actually not aware of the involuntary limb movements. The limb jerks are more often reported by bed partners. Patients experience frequent awakenings from sleep, non-restorative sleep, daytime fatigue, and/or daytime sleepiness.

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