What Is Periodic Limb Movement Disorder (PLMD)?
Periodic Limb Movement Disorder (PLMD), formerly known as nocturnal myoclonus, is a condition in which a person’s legs or arms twitch or move involuntarily and periodically during sleep. PLMD is not the same as night muscle spasms, or hypnic jerks, that occasionally occur when a person is falling asleep. These jerks are normal.
The limb movements typically occur 20 to 30 seconds apart, 5 or more times an hour, on and off throughout the night during periods of non-REM sleep. The rhythmic episodes usually involve a partial flexing of the big toe, ankle, knee, and occasionally, the hips.
The affected individual is usually unaware of the repetitive motion or the accompanying brief awakenings that disrupt sleep. Thus, people who have PLMD usually complain of difficulty in falling asleep, staying asleep, or staying awake during the day. They may also note restless sleep, hot or cold feet, or hair wearing off their legs. Bed partners often report being kicked, fighting for bed covers, or being awakened by the movements.
What Causes Periodic Limb Movement Disorder?
The cause of PLMD is unclear. Some researchers suggest PLMD is caused by reactions in the brain, while others suggest it might originate in the spinal cord. It may also be associated with circulatory problems. PLMD is often seen in patients with kidney disease, metabolic disorders, rheumatoid arthritis, pregnancy, or circulatory problems.
PLMD becomes more common as people age – around 34% of people over the age of 60 have PLMD. It occurs in men and women equally. This disorder is not very common in people under 30 years of age. Many people with PLMD also have Restless Legs Syndrome.
How is PLMD Diagnosed?
To diagnose PLMD, leg movements are recorded during sleep. Sensors placed over the calf muscle record the number of leg movements during each hour of sleep. This is called the Periodic Limb Movement index. If this index is greater than or equal to five, i.e., leg movements occurred at least five times an hour, then the diagnosis of PLMD is made.
Many people with PLMD do not require treatment because they sleep soundly and do not suffer from excessive daytime sleepiness or insomnia. For light sleepers, consulting with a personal doctor or a sleep specialist is recommended if symptoms of PLMD interfere with daily activities. PLMD is commonly associated with Restless Legs Syndrome (RLS), daytime sleepiness, and fatigue.
Relaxation therapy and good sleep practices encourage sound sleep in some PLMD patients. Refer to Sleep Tips for Successful Sleep for behaviors that help improve sleep.
The first step in treating any sleep disorder is to ascertain any underlying causes. Anemia, diabetes, or the use of certain antidepressants can contribute to leg movements. Often treatment of these underlying problems can relieve the symptoms of PLMD.
Various medications may help the person suffering from PLMD. Sleeping pills prevent the sleeper from frequent awakenings, but do not subdue the leg movements. Painkillers reduce the number of leg movements, but have little effect treating insomnia.
To date, drugs used to treat Parkinson’s disease seem to be the most effective – they treat both the movements and the insomnia. Drugs such as Sinemet (carbidopa or levodopa) and Mirapex (pramipexole dihydrochloride) are commonly used in this regard. Their side effects are minimal. However, the effects of long-term use in younger adults are unknown. Because PLMD is usually not treated with medication unless in combination with RLS and other symptoms, refer to “How is RLS Treated?” in the Introduction to Restless Legs Syndrome.
Vitamin and mineral supplements have shown to have some success treating PLMD. However, this treatment has not been proven clinically. Vitamin E may alleviate PLMD symptoms if poor peripheral circulation is the cause. Relaxation therapy and good sleep practices encourage sound sleep in some PLMD patients.