Periodic limb movement disorder (PLMD) is a rare sleep disorder characterized by periodic, repetitive movements of the legs and feet during sleep. In some cases, the disorder also affects the arms. If you have PLMD or sleep with someone who has PLMD, you may recognize these movements as brief muscle twitches, jerking movements, or an upward flexing of the feet. PLMD can disrupt sleep and co-occur with other sleep disorders, including restless legs syndrome and narcolepsy.
What Is PLMD?
Periodic limb movement disorder, referred to as PLMD, is a sleep disorder that affects approximately 4% to 11% of the population. People with PLMD experience repetitive jerking, cramping, or twitching of their lower limbs during sleep. These are known as periodic limb movements (PLMS) and happen every 5 to 90 seconds for up to an hour. The movements disrupt the person’s sleep — even if they don’t wake up — and cause daytime sleepiness and fatigue as a result.
Because the movements occur during sleep, the affected individual may not realize they have a sleep disorder. They’ll notice symptoms like waking up during the night for no apparent reason or feeling excessively tired during the day. As a result, they may believe they have insomnia. It is more common for a sleep partner to notice the movements and mention them to the affected individual.
PLMD can occur at any age, although it is quite rare among children. Comorbid sleep apnea or a neuropsychiatric disorder increase a child’s risk, as can having a parent with RLS. The risk for PLMD increases significantly with age, and as many as 45% of older adults exhibit symptoms. PLMD affects men and women equally.
What Causes PLMD?
PLMD can be a primary or secondary disorder, meaning that it either appears on its own (primary) or is caused by another medical condition (secondary). In the case of primary PLMD, scientists still do not know what causes the condition. Two potential causes are dopamine deficiency or miscommunication between nerves along the spinal cord.
In cases of secondary PLMD, the condition may be attributed to:
- Iron deficiency
- Caffeine use
- Spinal cord injury or tumor
- Other sleep disorders such as restless leg syndrome (RLS), narcolepsy, REM sleep behavior disorder, or sleep apnea
- Neurodevelopmental disorders like attention deficit hyperactivity disorder (ADHD) or Willam’s syndrome
- Side effect of certain medications, including tricyclic antidepressants, neuroleptics, anti-nausea drugs, and lithium
- Withdrawal from sedative medications, including barbiturates and benzodiazepines
While PLMD can co-occur with other sleep disorders, it most frequently occurs with RLS. Between 80 to 90 percent of people with RLS also have PLMD.
PLMD is often confused with RLS because both conditions involve symptoms affecting the legs, but they’re not the same, and they are diagnosed and treated differently. The symptoms of RLS occur while the person is still awake, while PLMS occurs during sleep. The physical sensations are also different. With RLS, the person experiences uncomfortable tingling or crawling sensations in the legs, accompanied by an uncontrollable urge to move them in order to feel relief. With PLMD, the legs repeatedly jerk or twitch, often unbeknownst to the sufferer.
What Are the Symptoms of PLMD?
The main symptoms of periodic limb movement disorder include poor sleep, daytime sleepiness, frequent awakenings, and rhythmic movements involving one or both legs during sleep. To be characterized as PLMS, the movements must:
- Involve one or both limbs, with a tightening, bending, or flexing of the knee, ankle, or big toe
- Occur in light non-REM sleep, typically during the first half of the night
- Last two seconds at a time, and repeat every 5 to 90 seconds at least 15 times per hour
The leg movements of PLMD can vary in nature from night to night, ranging from mild to severe. They may also occasionally involve the hips and upper arms. What makes the movements distinct is their repetitive nature and the occurrence during sleep.
How Is PLMD Diagnosed?
People may live with PLMD undiagnosed for some time. They may not even notice an impact on their sleep quality. It’s actually more common for their sleep partner to experience disrupted sleep due to the movements. People typically seek treatment after their sleep partner notices the symptoms or once the other symptoms — such as daytime sleepiness or fatigue — begin to interfere with their daily functioning and wellbeing.
If you think you or your sleep partner may have PLMD, talk to your doctor. At your appointment, they will ask questions to better understand your sleep issues and determine if they may be caused by an underlying issue like an iron deficiency or diabetes. They may review your personal and family medical history, any medications you take, and your current sleep and lifestyle habits. Your doctor may collect a urine or blood sample, or order additional tests, to rule out another condition.
If your sleep partner describes your leg movements and your doctor suspects PLMD or a sleep disorder, they may refer you to a sleep specialist. A sleep specialist may order an overnight sleep study, known as a polysomnogram. While you sleep, your breathing will be monitored (to rule out sleep apnea), as will your leg movements and other vitals. If the leg movements occur at least 15 times per hour you may receive a diagnosis of PLMD.
What Are the Treatments for PLMD?
Cases of secondary PLMD may go away if you address the underlying issue. There is no cure for primary PLMD, but treatment can significantly relieve symptoms and help improve sleep. Treatment for periodic limb movement disorder may include a mix of lifestyle changes and medication, depending on the severity of symptoms.
Cases of mild to moderate PLMD may be treated with lifestyle changes to improve sleep, such as incorporating more iron into your diet. Your doctor may recommend reducing or eliminating your caffeine or alcohol intake. They may also recommend stress management techniques likes deep breathing exercises, meditation, or yoga. Better sleep habits, such as sticking to regular bed and wake times and following a bedtime routine, can also help.
In cases of severe PLMD, doctors may prescribe medication to either reduce the PLMS or help the person sleep through it. These include many of the same medications prescribed for RLS, including benzodiazepines, melatonin, dopaminergic agents, gabapentin, and GABA agonists. Clonazepam, in particular, has been proven to reduce the total number of leg movements a person experiences per hour.
With proper treatment, the symptoms of periodic limb movement disorder are manageable. If you’re having trouble sleeping, consult your doctor.
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