What are Periodic Limb Movements?
Periodic Limb Movements during Sleep (PLMS) are repetitive, involuntary movements of the limbs (usually legs), typically occurring in sleep at regular intervals (every ~20-40 seconds), each lasting a few seconds. They may result in arousals or sleep fragmentation, though people often are unaware of them. If these movements lead to symptoms like poor sleep quality or daytime tiredness, the condition may be called Periodic Limb Movement Disorder (PLMD).
The Study: PLMs in Persons with Epilepsy (PWE)
A study recently published in Epilepsy Research examined how common PLMs are in people with epilepsy, and how these compare with people suspected of having obstructive sleep apnea (OSA).
The study was retrospective, reviewing sleep lab (polysomnography) data over about 10 years.
They took adults diagnosed with epilepsy who had sleep studies, and matched them to a control group of similar age, sex, and with similar levels of suspected OSA.
In the epilepsy group, there were different types of epilepsy (focal onset, generalized), and many were on multiple anticonvulsant medications; some were medically refractory.
What They Found
Prevalence of PLMs
In the epilepsy group, about 23% had detectable PLMs.
In the matched control group (suspected OSA), prevalence was similar—about 26%.
PLM Indices
The mean PLM Index (PLMI, number of periodic limb movements per hour) was ~ 6.1 ± 16.8 in the epilepsy group vs ~ 8.8 ± 20.7 in controls.
The PLMs with arousals (i.e. movements that lead to or accompany waking/arousal from sleep) were also similar between the groups.
Associated Factors
The only clear factor that was associated with having PLMs in the epilepsy group was older age.
They did not find strong associations between PLMs and seizure type (focal vs generalized), the number of antiseizure medications, or how well the seizures were controlled.
What This Means
Although people with epilepsy frequently have sleep disturbances, this study suggests that the rate of PLMs in PWE is not higher than in other populations with sleep concerns (here, those suspected of OSA). So PLMs may be common among PWE, but perhaps not uniquely so.
The presence of PLMs could contribute to poorer sleep quality in PWE — which matters, since good sleep is known to affect epilepsy: worse sleep can exacerbate seizures (or at least complicate seizure management). Even if PLMs are not more frequent in epilepsy, their effects might still be clinically important.
Older age as a risk factor implies that as people with epilepsy age, PLMs may become more relevant to assess. Also, comorbid conditions (like OSA) could interact or confound the findings. Indeed, since the control group were people suspected of OSA, there may be overlap of causes of sleep disruption.
Limitations & Open Questions
-
Because this was a retrospective chart review, it depends on the quality and consistency of past sleep studies and records. Some variables (for example, how sleep was disrupted, subjective sleep quality etc.) might not have been captured fully.
-
The study cannot tell us causation — i.e. whether PLMs directly worsen epilepsy outcomes, or whether worse epilepsy (or its treatment) promotes more PLMs.
-
It’s also not clear whether treating PLMs (if present) in PWE would lead to improvements in seizure control, quality of life, or daytime functioning.
-
Another question: some antiseizure medications have sedative effects or affect sleep architecture; could these influence PLMs (either increase or mask them)? The study didn’t find a strong link with number of medications, but more detailed work might look at types of drugs, dosages, etc.
-
Also, overlap with other sleep disorders (like OSA, restless legs syndrome) remains an area to better delineate: disentangling what is due to PLMs vs. what is due to other disorders is important for both diagnosis and treatment.
Clinical Implications
For clinicians treating epilepsy, it may be worth assessing for PLMs (via sleep history, and polysomnography when indicated), especially in older patients or those complaining of poor sleep, daytime somnolence, or fragmented sleep.
Improving sleep (by identifying and treating sleep disorders including PLMs, OSA, etc.) might help in optimizing seizure control and overall quality of life.
Sleep medicine specialists and neurologists should collaborate for comprehensive management in PWE, not focusing solely on seizure control but also on sleep health.
