Periodic Limb Movement Disorder is a sleep disorder that causes rhythmic, repetitive involuntary jerking or flexing of the legs and, in some cases, the arms during sleep. These movements typically occur during non-rapid eye movement (NREM) sleep and can affect the toes, ankles, knees, and hips. In this blog, we’ll break down the condition, explore its symptoms and causes, and provide advice for anyone struggling with the disorder and unsure of what to do.

It is usually not life-threatening, but it can become a cause for concern if sleep disruption causes chronic fatigue, mood disorders, or cognitive issues. Secondary PLMD can also be a sign of underlying health issues such as iron deficiency or kidney disease.

• Daytime Fatigue: Waking up briefly and frequently over the course of a night can lead to daytime tiredness and poor concentration.
• Mental Health: Linked to higher rates of anxiety, irritability, and depression.
• Heart health: Repeated nighttime jerks and blood pressure spikes may increase long-term cardiovascular stress.
• Underlying causes: Often connected to low iron, nerve damage, or metabolic, and kidney conditions.

PLMS refers to the physical jerks or movements of the legs and arms that occur during sleep. PLMD (Periodic Limb Movement Disorder), however, is the clinical sleep disorder diagnosed when those movements occur frequently enough to disrupt sleep and cause daytime fatigue.

PLMS can happen without causing health issues or having consequences in the daytime. It is common in older adults or people with restless legs syndrome (RLS) and is not recognised as a disease on its own.

PLMD on the other hand is defined by a high frequency of movements and must involve clinical symptoms such as extreme daytime sleepiness, poor quality sleep, or frequent wakeups during sleep

In the case of PLMD, disrupted sleep must be caused by involuntary limb movements. It can’t be caused by other conditions such as sleep apnoea.

Most people with PLMD don’t know their legs are moving. A bed partner often notices first – kicking in the night, or the covers ending up on the floor. What you might notice yourself is sleep that doesn’t refresh you, or tiredness during the day. PLMD can only be diagnosed with an overnight sleep study; a sleep tracker or smartwatch can’t tell you.

PLMD is diagnosed when a sleep study shows more than 15 limb movements an hour in adults (more than 5 in children), the movements are disturbing your sleep or your days, and nothing else explains the problem better. That includes restless legs syndrome: if you have RLS, the movements are counted as part of it, and PLMD isn’t diagnosed separately. Other sleep disorders, such as sleep apnoea, need ruling out too.

PLMD more often causes tiredness and unrefreshing sleep than strong sleepiness. If you’re falling asleep during the day, see your GP, as other causes may need checking.

Treatment depends on what’s behind it, and it’s decided with a doctor, often a sleep specialist. The first step is usually a blood test to check your iron stores (ferritin), because low iron is one of the most common causes and one of the most treatable. Don’t start iron supplements without a blood test – too much iron is harmful.

Your doctor may also look at other health conditions and at any medicines you take, since some can make limb movements worse. Don’t stop or change a medicine without talking to whoever prescribes it.

There’s little good evidence for medicines that treat PLMD on its own, so for many people the focus is on the cause and on protecting sleep. Things that may help: cutting down on caffeine, alcohol and nicotine, especially later in the day; keeping a regular wake-up time; and moving your body during the day.

The two can be related; however, PLMS does not cause Parkinson's disease. While PLMS can occur in anyone, it is more common in people with Parkinson's disease than in the general population.

Both conditions involve issues in how the brain handles dopamine and processing in the nervous system. They share treatment too; medications that boost dopamine, (dopamine agonists), are often used to manage Parkinson’s motor symptoms and severe limb movement disorders.

However, there are also several differences between the two:

• PLMS: A person experiences involuntary, repetitive leg or arm jerks or kicks only during sleep, which disrupts sleep.
• Parkinson's: A progressive neurodegenerative disorder that involves daytime tremors, muscle stiffness, slow movement, and balance issues.

Periodic Limb Movement Disorder does not typically go away completely by itself because it is often a chronic condition. However, symptoms can improve majorly, go into remission, or disappear entirely if they are connected to a treatable underlying health issue like iron deficiency or managed with lifestyle changes and medication.

It is important to consult a medical professional therefore so you can get to the root cause and hopefully find a way to manage your symptoms and improve your sleep routine.

It normally happens during the lighter, non-REM (NREM) sleep stages, specifically stage N1 and stage N2 and during the first half of the night. Movements are normally absent during REM sleep because of normal muscle paralysis.

These movements normally look like flexions of the toes, ankles, knees or hips and occur every 20-40 seconds.

Earlier studies suggested that children with ADHD had more limb movements in sleep. A 2023 review of 33 studies found no difference, so that link is now in doubt. Restless legs and low iron are a different story. In one study of adults with ADHD, a third had restless legs syndrome. If you have ADHD and your legs feel restless in the evening, or a partner notices you kicking at night, it’s worth asking your GP to check your iron.

See your GP if you’re tired most days despite enough time in bed, if a partner notices you kicking or jerking at night, or if your legs feel uncomfortable or restless in the evening. Ask about a ferritin test, and whether a referral for a sleep study would help. When it might be a sleep disorder has more on the signs worth checking.