RLS Introduction and Definition

Restless Legs Syndrome (RLS), also called Willis-Ekbom disease, is a common but often misunderstood neurological condition. For patients and families, the first step in dealing with RLS is to understand what it is, how it was discovered, and what doctors mean when they talk about the “essential criteria” for diagnosis. This article introduces the history, definition, and key features of RLS in a way that is accessible but still medically accurate.

A Brief History of RLS

Although RLS has gained attention only in recent decades, the condition has been described for centuries.

1672: The English physician Thomas Willis first wrote about people who experienced unusual restlessness in their legs at night.
1861: The German doctor Theodor Wittmaack gave the condition a Latin name, “Anxietas tibiarum” (literally, “anxiety of the legs”).
1923: The neurologist Hermann Oppenheim noted that this was a distinct neurological disorder and even observed that it tended to run in families.
1945: The Swedish neurologist Karl-Axel Ekbom published a detailed scientific description, including most of the symptoms we recognize today. He also coined the name “Restless Legs Syndrome,” which remains in use worldwide.

Since Ekbom’s time, research has advanced enormously. Scientists have identified genetic factors, discovered links to iron metabolism and dopamine activity in the brain, and developed effective treatments. Yet RLS is still underdiagnosed and sometimes misunderstood.

What Is RLS?

RLS is classified as a sensorimotor disorder, meaning it affects both sensations (what you feel) and motor functions (how your body moves). The main feature is an irresistible urge to move the legs, usually accompanied by unpleasant feelings deep inside the legs. Sometimes the arms or other body parts are also involved, but legs are the most common.

The urge to move and the sensations typically:

Begin or worsen during periods of rest or inactivity.
Improve temporarily when the person moves—by walking, stretching, or shaking the legs.
Are strongest in the evening or at night, often disturbing sleep.
Cannot be fully explained by another medical or behavioral condition, such as muscle cramps, arthritis, or poor circulation.

These points form the five essential diagnostic criteria used worldwide by neurologists and sleep specialists.

The Five Essential Diagnostic Criteria

For a doctor to diagnose RLS, the following must all be present:

An urge to move the legs
- The feeling is nearly impossible to resist.
- It often comes with unpleasant sensations like tingling, crawling, pulling, or even pain.
- Some patients say it feels like “electricity” in the legs or as if “something is crawling under the skin.”
Worsening at rest
- The sensations typically appear when sitting still or lying down, such as while watching a movie, attending a meeting, or going to bed.
Relief through movement
- Walking, stretching, or even briefly moving the legs brings partial or complete relief—though usually only as long as the movement continues.
Evening or nighttime predominance
- Symptoms are clearly worse in the evening or night compared to daytime.
- This daily rhythm is called a circadian pattern, and it explains why RLS often leads to insomnia.
Not better explained by another condition
- RLS must be distinguished from other disorders like leg cramps, venous disease, arthritis, neuropathy, or simply nervous habits like tapping the foot.

Additional Notes About the Criteria

Children: RLS can occur in children, but they often describe it differently. Instead of “tingling” or “pulling,” they might say their legs feel like “growing pains.”
Severe cases: When symptoms are very strong, patients may not notice the improvement with movement or the worsening at night. Doctors still apply the criteria if these features were present earlier in the disease.
Misdiagnosis: Conditions like varicose veins or arthritis may resemble RLS, but careful history-taking usually clarifies the difference.

Three Main Components of RLS

Although symptoms vary, RLS typically involves a triad:

The urge to move – the central experience, sometimes without sensations.
Unpleasant feelings – described in many ways: burning, aching, itching, buzzing, or deep pain.
A time pattern – worse in the evening and at night, leading to sleep disturbance.

Together, these three components explain why RLS is both a neurological and a sleep-related disorder.

How RLS Is Classified

Doctors sometimes distinguish between:

Primary (idiopathic) RLS: Occurs without another known disease, often with a family history.
Secondary RLS: Appears in connection with other conditions such as kidney disease, iron deficiency, pregnancy, or use of certain medications.

However, research increasingly suggests that both forms may share underlying genetic and neurological mechanisms. Secondary factors may simply “trigger” the symptoms in someone who is already susceptible.

Why RLS Matters

Patients often assume that RLS is just a “quirk” or minor problem. In fact, it can seriously disrupt quality of life:

Sleep disruption: People with RLS may take hours to fall asleep, wake up repeatedly, or wander at night trying to relieve the discomfort.
Daytime fatigue: Poor sleep leads to tiredness, irritability, reduced concentration, and sometimes depression.
Social and occupational effects: Attending a concert, sitting through a long meeting, or traveling on a plane can be extremely difficult.

When untreated, RLS can impair work, family life, and overall well-being as much as many chronic illnesses.

Summary

Restless Legs Syndrome is a well-defined neurological condition with a long history of medical recognition. Its core features are the irresistible urge to move, the relief through movement, and the worsening of symptoms during rest and at night. Though it may sound simple, these symptoms have a profound impact on sleep and quality of life. Understanding the definition and criteria is the first step for patients and families in recognizing the condition, seeking medical help, and exploring treatment options.