Introduction

Restless legs syndrome (RLS) and periodic limb movement disorder (PLMD) are two types of common movement disorders that are still not fully understood. RLS is manifested by urges to move that take place during rest and disappear during movement. People with RLS often demonstrate periodic leg movements during sleep or rest.

Periodic limb movements typically occur in sleep, manifesting as repetitive flexions of the ankles, and knees. These are termed Periodic limb movements in sleep (PLMS). Although RLS and PLMS can occur independently of each other, they share common causes and mechanisms of origin. Due to this, they can co-occur. 

Severe forms of these disorders can negatively affect sleep, mood, and the overall quality of life. A diagnosis of PLMD is made by polysomnography, an instrumental diagnostic method. RLS is a clinical diagnosis that is determined by a physician based on several factors. Unfortunately, doctors are not always able to recognise RLS, so it is often misdiagnosed and mistreated.^1,2,3

This article will shed light on the prevalence, risk factors, methods of prevention, mechanisms of origin, common symptoms, and treatment of RLS and PLMD.

Prevalence

The prevalence of RLS and PLMD varies according to country, age, gender, and comorbidities:^2,4

• Country: The prevalence of RLS is significantly higher in Europe and North America, ranging from 5% to 13%, than in Asia (up to 3%) 
• Age: The prevalence of RLS and PLMD increases with age. RLS usually occurs between the ages of 30 and 40. However, RLS can appear at any age, rarely in childhood. Later cases are more often related with more severe symptoms
• Gender: The prevalence of RLS and PLMD in those assigned female at birth (AFAB) is higher than in those assigned male at birth (AMAB). During pregnancy, the likelihood of RLS is higher: one in five pregnant women suffers from RLS. The symptoms of RLS usually peak in the third trimester of pregnancy and disappear after labour. However, RLS can reappear later in life. It is four times more likely to reoccur than in those who did not have RLS during pregnancy

Periodic limb movements in sleep (PLMS) are present in 90% of people with RLS. However, PLMS can occur without RLS and is found in 25% of people undergoing routine polysomnography.³

Risk factors and prevention

Lifestyle factors 

There is a growing body of research on the role of lifestyle factors in the prevalence of RLS and PLMS. The following are considered risk factors for both disorders: 

• Lack of physical activity
• Stress 
• Shift work
• Caffeine consumption

Therefore, a healthy lifestyle is essential for the prevention of RLS. Regular physical activity makes the greatest contribution.^2,4

Genetics 

However, genetic predisposition is also an important contributing factor to RLS and PLMS. It has been identified that certain genes associated with RLS may increase the incidence of PLMS.⁴ According to studies, up to 60% of people with RLS have relatives with this disorder. In familial RLS, symptoms tend to start earlier.²

Mechanisms of origin

Although the causes and mechanisms of RLS and PLMS are still unclear, they are considered complex conditions in which genetic and environmental factors predispose individuals to the disease and influence the onset of symptoms. Researchers identified mechanisms that are thought to play a significant role in the onset and treatment of these disorders.^2,4

Iron deficiency in the brain

The prevalence of RLS and PLMS can be related to iron deficiency. RLS occurs four to six times more in people with iron deficiency than in the general population. However, most patients with RLS have a brain iron deficiency rather than a generalised iron deficiency throughout the body, which is confirmed by magnetic resonance imaging (MRI) data. Moreover, the processes of iron transport to the brain and iron absorption by the brain are disturbed.^2,4

Dopamine dysregulation

Dopamine is a substance released by brain neurons to send signals to other neurons in the body. Dopamine can transmit signals through a variety of pathways, being responsible for motivation and behaviour, motor function, and the release of various hormones. These signals’ pathways are called the dopamine system.⁵

The involvement of the dopamine system in the mechanisms of RLS and PLMS is supported by the therapeutic effects of medicines affecting this system.^2,4

Symptoms 

RLS is manifested by the urge to move the legs, usually with discomfort in the legs. In up to a half of cases, other parts of the body are involved, especially the arms. People with RLS usually report that symptoms occur "deep" in the muscles or tendons.²

Symptoms start or exacerbate during periods of rest, such as lying or sitting, and stop or decrease with movement. Symptoms are common in certain situations, such as sitting in a car as a passenger, flying long distances in a plane, or sitting in a cinema or theatre. 

Sleep disturbances 

Approximately 60-70% of people with RLS experience sleep disturbances, including difficulty falling asleep, decreased total sleep time, and an increased number of awakenings with RLS symptoms. 

Insomnia caused by RLS usually takes place in the first half of the night. Other signs of chronic sleep disturbance, such as fatigue, difficulty concentrating, or depressive symptoms, may occur. However, they are not often accompanied by intense sleepiness and the need for a nap.²

Diagnosis

According to the International Classification of Sleep Disorders, the diagnosis of PLMD is made if: 

• The number of PLMS is more than 15 times per hour in adults 
• More than 5 times per hour in children 
• Sleep problems or daytime impairments are present 

In line with the American Academy of Sleep Medicine, the diagnosis criteria for PLMS are:^3,4 

• Leg movements with a duration of 0.5 to 10 seconds 
• Movements are repeated every 5-90 seconds 
• Movements occur in a series of at least four movements in a row 
• Movements have an amplitude of at least 8 μV during polysomnography

Symptom relief

While each person may have their own strategy for symptom relief, the most commonly reported strategies are²: 

• Walking 
• Stretching 
• Massaging the affected limbs
• Other activities such as dousing the limbs with cold water 
• Stepping on the floor barefoot

In most people with RLS, symptoms are worse in the evening or at night than during the day or present only in the evening or at night. However, in severe cases, symptoms may occur throughout the day. Vigorous activity during the day may aggravate symptoms in the evening or at night.²

Treatment

Unfortunately, RLS and PLMS are still incurable in many cases. Therefore, treatment focuses on symptom mitigation, which can be effectively managed if treatment is timely and appropriate. 

However, the main problem is that RLS is often misdiagnosed. For this reason, patients with RLS often don’t receive timely and adequate treatment. This leads to symptom exacerbation and needless suffering. Please see a doctor at the first sign of symptoms. Doctors may recommend the following: 

• First, the assessment of systemic iron status 
• Appropriate treatment of iron deficiency, if needed 
• Management of comorbid sleep disorders 
• Assessment of the impact of medication that may aggravate or cause RLS 

For infrequent and mild RLS and PLMS, non-pharmacological strategies can be recommended first. They include: 

• Regular physical exercise (including yoga) 
• Magnetic or electrical stimulation techniques 
• Acupuncture 
• Lifestyle modifications 

Pharmacotherapy includes: 

• Iron therapy 
• Dopaminergic drugs 
• Gabapentin
• Low-potency opioids 

Any medical treatment can only be prescribed by a doctor. Medicines for the treatment of RLS and PLMS have contraindications and side effects. Your doctor will discuss with you the benefits and drawbacks of the medications.^2,4

FAQs

What is restless legs syndrome?

Restless legs syndrome (RLS) is a common disorder manifested by urges to move that take place during rest and disappear during movement. People with RLS often demonstrate periodic leg movements during sleep or rest.

What is periodic limb movement disorder?

The disorder of periodic limb movements, or PLM, is also called sleep-related myoclonus syndrome or nocturnal myoclonus syndrome. These movements of the ankles, knees, and hips during sleep are periodic and have stereotyped behaviour. 

What can cause restless legs syndrome and periodic limb movement disorder?

Three main factors cause primary restless legs syndrome and periodic limb movement disorder:

• Genetic background 
• Disorders of the dopamine production system 
• Iron deficiency

What does a person with restless legs syndrome feel?

Restless legs syndrome (RLS) is manifested by the urge to move the legs, usually accompanied by discomfort in the legs. In up to half of cases, other parts of the body are involved, especially the arms. People with RLS usually report that symptoms take place "deep" in the muscles. Approximately 65% of people with RLS experience sleep disorders, including difficulty falling asleep, decreased total sleep time, and an increased number of awakenings with RLS symptoms.

How can you help yourself with restless legs syndrome and periodic limb movement disorder?

Please see a doctor at the first sign of symptoms. While you are waiting for an appointment, you can try these ways to relieve symptoms: regular physical exercise or yoga, healthy sleep habits, and avoiding caffeine.

Summary

Restless legs syndrome (RLS) and periodic limb movements in sleep (PLMS) are common but misdiagnosed disorders that cause discomfort, reduce the quality of life, and increase the risk of other diseases. Therefore, it is important to see a doctor immediately at the onset of the first symptoms and to prevent the disorder through regular physical activity and a healthy lifestyle.