Periodic limb movement disorder (PLMD), also classified as nocturnal myoclonus, is a sleep disorder in which one or more of the subjects limbs will involuntarily move during sleep. The degree to which this occurs and its frequency varies. Some people with PLM’s will only experience mild symptoms such as slight twitches or ‘shudders’ (periodic limb movement syndrome (PLMS)), while others will have movements best characterized as thrashing or wailing. Those with extreme movements may find themselves waking up at their own movements, and will almost certainly disturb and arouse their partners. Couples are often forced to sleep in separate beds when one or both of them have advanced cases of PLM.
Not everyone with PLM’s is considered to have PLMD though. Those with only mild forms of PLMS that suffer no consequences from the involuntary limb movement, such as waking up themselves or others, are classified as having periodic limb movements of sleep (PLMS), for which it is considered unnecessary to seek treatment for. In rare cases PLMS can also occur while awake, called periodic limb movements of wakefulness (PLMW).
In addition to actual physical movement of the limbs, many people with PLM will experience involuntary tightening or flexing of the muscles, which can be quite painful and disconcerting, and causes the subject to wake up at a high frequency. PLM can occur throughout the night, but in most patients occurs in batches, lasting from 30 minutes to 2 hours on average, with actual movements happening every 5 to 90 seconds during that span. Physical movements are likely to occur in both limbs, while involuntary tightening or flexing of the muscles is more likely to occur in just one limb. PLM typically occurs in the slow-wave phase of sleep just before the deep sleep of REM (rapid eye movement) sleep.
PLM is found with high frequency in those suffering with restless legs syndrome, with as many as 85% of people with RLS also having PLM. Conversely, the number of people with PLM also having RLS is quite low, owing to the fact that PLM is somewhat more common than RLS. Like RLS, PLM can occur in the legs or arms, but most often appears in the legs.
PLM is found in 5% of adults over 30, and nearly 50% of adults over the age of 65, lending credence to the claim that it is tied to the immune system, and more likely to appear in those with weaker immune systems. It occurs rarely in children. Detailed studies of it have not been conducted though, so detailed statistics on the variance between genders, and its genetic disposition are unknown with any certainty.
PLM has roots in other sleeping disorders, is more likely to occur in patients with those disorders. This includes the aforementioned RLS, as well REM sleep behaviour disorder and narcolepsy. Like RLS, it may also have a connection to low iron levels, specifically low iron levels in the brain.
A link has also been found between people with spinal cord injuries having a higher prevalence of PLM.
Because of the nature of the disorder, many people may not know they are suffering from it until told by another, as in most cases the PLM will not cause the subject to rouse. Only in the case of extreme jerks or movements, or painful tightening of the muscles is the subject likely to awaken. In all but the most severe cases, treatment will not need to be sought, but as it may be tied to another disorder or medical condition, a doctor should still be consulted concerning it.
The polysomnogram (overnight sleep study) is the best method for detecting the severity of the movements, and also for detecting any other possible sleeping disorders that may be contributing to it.
Treatment for PLM is similar to the treatment for RLS, so someone with both conditions will likely find relief from both syndromes with one treatment. This includes iron supplements when low iron levels are considered to be at the root of the problem and anti-seizure medications. For extreme cases, sleeping pills or pain killers may be prescribed.
Additionally, changes in your daily routine will probably be recommended. This includes a healthier diet and balanced exercise schedule. Most important is to implement good sleep hygiene practices. This will improve the speed you reach REM sleep, and your ability to stay in it. The chances of PLM occurring during REM sleep are much lower than while in earlier sleep phases. Good sleep hygiene includes improving the sleep conduciveness of the environment you sleep in, having a comfortable bed and pillow that is right for you, and avoiding stimulants of any kind before bed time.
Reviewed September, 2007