Periodic Limb Movements (PLMs), also known as nocturnal myoclonus, are characterized by repetitive movements of the limbs during sleep. The movements can result in several arousals or awakenings during the night. If the movements wake you up, then you may feel like you have insomnia because you can’t seem to stay asleep. If the movements only cause arousals, small changes in brainwave patterns, you may feel like you have excessive daytime sleepiness because even though you are not waking up, your sleep is still disturbed. People are usually unaware of the movements because they are small and occur while you are asleep.
Leg movements consist of an extension of the big toe in combination with partial flexion of the ankle, knee and sometimes hip. Arm movements usually consist of a flexion of the forearm in combination with the wrist. There can be night-to-night variability in the number of movements and as you get older PLMs often get worse. Approximately 34% of people over 60 have PLMs.
Here’s a few points to remember when trying to figure out what is going on during your sleep.
PLMs:
- Cause a fragmented or restless sleep
- Make you feel like you have maintenance insomnia or excessive daytime sleepiness
- Can occur immediately with the onset of stage 1 sleep
- Are worse in stage 2 sleep
- Decrease in frequency during stages 3 & 4
- Are usually absent during REM sleep because our bodies naturally lose all muscle tone while in REM sleep
- Can be associated with a specific brainwave pattern called a K-complex and are also associated with arousals and awakenings
When sleep professionals look for PLMs, they look for:
- Repetitive muscular contractions each lasting 0.5-5 sec.
- Usually both limbs move at same time
- An interval of 20-40 sec. between movements
- Movements separated by intervals of less than 5 sec. or more than 90 sec. are not counted in the total number of clinically significant movements
- A minimum of four movements per episode
When limb movements become a problem: Calculating a PLM & PLM-arousal Index
An overall PLM Index is calculated to determine the number of movements per hour of sleep. Movements occurring on separate limbs are added together. Five or more movements per hour of sleep are considered clinically significant.
A PLM-arousal Index is calculated to determine the number of PLMs associated with an arousal per hour of sleep. An index of five or more is clinically significant.
Do you feel like you have insomnia or do you feel tired all the time, even after a night of sleep?
You might have PLMs.