Periodic limb movements in sleep: causes, symptoms and treatment

Periodic limb movements in sleep, sometimes written as PLMS, are repetitive movements of the limbs that happen while you are asleep. The Brain Charity describes periodic limb movement disorder (PLMD) as a repetitive twitching and jerking of the limbs that is more common in the legs but can also affect the arms, and that usually happens at night.

GPnotebook, a reference used by UK GPs, gives more detail: the jerks last between 0.5 and 5 seconds, tend to come at 20 to 40 second intervals, are most often seen in the toes, feet and legs, and may be associated with brief arousals or awakenings from sleep. The older name for the same phenomenon was nocturnal myoclonus.

The difference between having periodic limb movements and having the disorder is whether they cause a problem. Many people have the movements on a sleep study without any symptoms. The label of a disorder is used when they are accompanied by disturbed sleep or daytime sleepiness that cannot be explained by something else.

The NHS describes restless legs syndrome (RLS) as a condition in which you have a strong urge to move your legs, usually when resting at night, often with uncomfortable feelings such as tingling, throbbing or itching. That is a sensation you are aware of while awake.

Periodic limb movements, by contrast, are involuntary and happen during sleep. Patient.info's professional reference notes that PLMD differs from RLS in that the movements are involuntary, and that it is present in about 80 percent of people with RLS. The two commonly occur together, which is why the same tests and treatments are often discussed for both. Periodic limb movements during sleep are also listed as a supportive feature in the diagnosis of restless legs syndrome.

The Brain Charity says the exact cause of PLMD is unknown, but research suggests it may involve an imbalance of the chemical dopamine, and it lists anaemia, arthritis, an underactive thyroid and fibromyalgia as other possible causes. The NHS links restless legs syndrome to iron and dopamine levels and lists pregnancy, iron deficiency anaemia, kidney disease and some medicines as associated factors.

GPnotebook adds that periodic limb movements may be associated with other sleep disorders such as sleep apnoea and narcolepsy, and with certain medicines including SSRI antidepressants such as fluoxetine and sertraline. It lists iron or folate deficiency, kidney disease, peripheral neuropathy, Parkinsonism and spinal disorders as other associations, and says caffeine and neuroleptic medicines can make the movements worse. It reports an overall prevalence of about 6 percent, rising with age, with up to 30 percent of people over 50 affected.

Because the movements happen in sleep, the clues are usually indirect. A partner may notice kicking or twitching. The sheets may be disturbed in the morning. The person may wake unrefreshed, feel sleepy in the day, or have trouble concentrating. The Brain Charity notes that PLMD can cause uncontrollable spasms through the night, affect daily activities, cause low mood and reduce quality of life.

• Repetitive kicking or twitching of the legs, and sometimes the arms, during sleep.

• Unrefreshing sleep or frequent waking, with no clear reason.

• Daytime sleepiness or tiredness.

• Restless legs symptoms in the evening, such as an urge to move and uncomfortable sensations.

• Low mood or reduced concentration linked to poor sleep.

A GP will usually begin with a history of the sleep problem, your medicines, caffeine and alcohol intake, and symptoms of restless legs. Blood tests to look for iron deficiency and other treatable contributors, such as thyroid or kidney problems, are a sensible first step; the NHS names iron deficiency anaemia and kidney disease as conditions linked to restless legs symptoms, and treating the underlying condition may help.

The Brain Charity states the diagnostic threshold of more than 15 limb movements per hour, a count that is hard to judge by watching alone and is usually established with overnight monitoring. Such a sleep study is not needed for everyone and is generally considered when the cause of daytime sleepiness or disturbed sleep is unclear or the problem is severe. Your doctor can tell you whether referral to a sleep service is appropriate.

GPnotebook says symptoms may respond to increased exercise or reduced caffeine intake, and that some people with excessive daytime sleepiness benefit from drug treatment such as dopamine agonists (for example pramipexole), gabapentin or pregabalin. The same options appear in the NHS restless legs guidance, which lists iron supplements where iron is low, medicines such as pregabalin or gabapentin and medicines that increase dopamine levels such as co-careldopa or ropinirole, and suggests that a doctor will check other medicines you take, because some can make symptoms worse.

The NHS sleep advice for restless legs is also useful: exercise during the day, a regular bedtime and wake time, a dark and quiet bedroom, a warm bath before bed, avoiding caffeine after midday, avoiding alcohol for at least 2 hours before bed and avoiding screens right before sleep. It advises seeing a GP if symptoms stop you sleeping, affect your mental health or have not improved with self-help.

Medicines should not be stopped or started without medical advice. If you take an antidepressant and think it may be involved, discuss it with your prescriber rather than stopping it.

GPs manage most cases, including blood tests and a trial of self-help or medicines. Sleep studies and specialist sleep or neurology clinics are available on the NHS by referral, and private sleep services also exist. Waiting times vary by area.