Periodic limb movement disorder (PLMD) is repetitive cramping or jerking of the legs during sleep. It is the only movement disorder that occurs only during sleep, and it is sometimes called periodic leg (or limb) movements during sleep. "Periodic" refers to the fact that the movements are repetitive and rhythmic, occurring about every 20-40 seconds. PLMD is also considered a sleep disorder, because the movements often disrupt sleep and lead to daytime sleepiness.
Symptoms of PLMD
The most common symptoms noted by people with PLMD are not leg movements but poor sleep and daytime sleepiness. Many people with PLMD are unaware of their leg movements unless their bed partner tells them.
- Leg movements involve one or both limbs.
- Typically the knee, ankle, and big toe joints all bend as part of the movements.
- The movements vary from slight to strenuous and wild kicking and thrashing.
- The movements last about 2 seconds (and thus are much slower than the leg jerks of myoclonus).
- The movements are rhythmic and repetitive and occur every 20-40 seconds.
Periodic Limb Movement Disorder (PLMD) and Restless Legs Syndrome) RLS) are distinct disorders, but often occur simultaneously. Both PLMD and RLS are also called nocturnal myoclonus, which describes frequent or involuntary muscle spasms/movements. The major difference is that RLS can occur while the patient is awake and may inhibit a person’s ability to fall asleep while PLMD occurs only while asleep and often the person is unaware of its presence.
Both disorders cause similar symptoms and the treatments are the same: eliminate aggravating factors such as caffeine and nicotine, investigate for disease that may cause/contribute, and pharmacologic treatment when indicated.