Restless Legs Syndrome

Intro

Restless legs syndrome (RLS), formally known as Willis-Ekbom disease, is a common and significantly under-recognised neurological condition. It affects an estimated 5–10% of adults in Western populations, yet many cases go undiagnosed for years or are dismissed as anxiety, growing pains, or simply fidgeting. For people with moderate to severe symptoms, RLS is one of the most disruptive sleep disorders — directly delaying sleep onset every night.

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Key Points

RLS is defined by four core features: urge to move the legs, worsening at rest, partial relief with movement, and worsening in the evening.
It is a neurological condition — not anxiety, “growing pains,” or habitual restlessness.
Iron deficiency is a major modifiable cause; ferritin should be measured in all cases and the treatment target is above 75 µg/L — higher than the conventional laboratory normal.
RLS is frequently missed because symptoms occur mainly at night, away from clinical observation.
Effective treatments exist: iron supplementation, dopaminergic medications, and alpha-2-delta ligands.

Symptoms

RLS is diagnosed on four core clinical criteria (International RLS Study Group):

An urge to move the legs, usually accompanied by uncomfortable sensations
Described as crawling, creeping, pulling, aching, throbbing, electric, or simply an irresistible need to move. In severe cases, sensations extend to the arms.
Worsening at rest — the urge begins or intensifies during inactivity: lying down, sitting in a cinema, long-haul flights
Partial or complete relief with movement — walking, stretching, or rubbing temporarily relieves symptoms
Worse in the evening or at night — symptoms follow a clear circadian pattern, peaking in the late evening and overnight

Impact on sleep: RLS delays sleep onset because lying down to sleep is the exact condition that triggers symptoms. Severe cases prevent sleep for hours. The resulting sleep deprivation causes daytime fatigue, mood disturbance, and impaired cognition — often the chief complaint that brings patients to a doctor.

Associated features:

Periodic limb movements in sleep (PLMS): Repetitive, involuntary leg jerks occurring during sleep in up to 80% of RLS patients. These may further fragment sleep and are sometimes noticed by bed partners.
Periodic limb movement disorder (PLMD): When PLMS causes clinically significant sleep disruption without accompanying RLS, it is classified as PLMD — a related but distinct diagnosis.

Causes and Risk Factors

Central dopamine dysregulation

RLS is associated with reduced dopaminergic transmission in the A11 diencephalospinal pathway, which regulates motor control in the spinal cord. The circadian pattern of symptoms — peaking in the evening — mirrors the circadian nadir of brain dopamine levels, explaining why symptoms worsen at night.

Iron deficiency

Iron is a cofactor in the rate-limiting step of dopamine synthesis. Low brain iron — detectable by low serum ferritin — reduces dopamine production and directly triggers or worsens RLS. Key findings from clinical research:

A substantial proportion of RLS patients have ferritin below 75 µg/L
Iron supplementation improves RLS severity even when ferritin is within the conventional “normal” laboratory range (typically 12–150 µg/L)
The treatment target for ferritin in RLS is above 75–100 µg/L, not merely “within range”

Genetic factors

RLS has a strong hereditary component. First-degree relatives of patients have approximately a 3–5-fold increased risk. Multiple susceptibility loci have been identified. Early-onset RLS (before age 45) tends to be more strongly familial.

Secondary causes

Conditions and medications that can trigger or significantly worsen RLS in susceptible individuals:

Pregnancy (iron depletion and hormonal factors)
End-stage renal disease (affects up to 25% of dialysis patients)
Peripheral neuropathy
Parkinson’s disease
Medications: antidopaminergics (metoclopramide, antipsychotics), antihistamines, many antidepressants (SSRIs, mirtazapine, TCAs), certain antiemetics
Caffeine and alcohol may exacerbate symptoms in susceptible individuals

Diagnosis

RLS is a clinical diagnosis — there is no definitive blood test or imaging finding.

A clinician will:

Assess the four core diagnostic criteria
Exclude mimics: leg cramps (no urge to move component), positional discomfort, peripheral neuropathy, venous insufficiency, anxiety-related restlessness
Assess severity using a validated tool such as the International RLS Rating Scale (IRLS)
Measure ferritin — essential in all cases; ferritin below 75 µg/L warrants iron treatment regardless of haemoglobin
Check full blood count, renal function, and fasting glucose to exclude secondary causes
Consider referral to neurology or sleep medicine for moderate-severe or refractory cases

A sleep study is not required for RLS diagnosis but may be arranged if periodic limb movement disorder is suspected or sleep disruption is severe and multi-factorial.

Treatment

Iron supplementation

Iron treatment is the first step when ferritin is below 75 µg/L:

Oral iron: Ferrous sulphate or ferrous fumarate, taken on an empty stomach where tolerated, with vitamin C to enhance absorption. Repeat ferritin in 3 months and continue until above 75–100 µg/L. GI side effects (nausea, constipation) are common; taking with food reduces them at the cost of some absorption.

Intravenous iron: Considered for patients with GI intolerance to oral iron, malabsorption, or persistently low ferritin despite oral treatment. Some centres use IV iron as first-line for moderate-severe RLS given faster and more complete repletion. Clinical response typically follows within 4–6 weeks.

Lifestyle and non-pharmacological measures

Sleep hygiene: A consistent sleep schedule and onset routine reduce symptom severity. The reduction in sleep pressure from irregular schedules worsens RLS.
Exercise: Moderate aerobic exercise and lower limb stretching reduce RLS severity over weeks. Intense exercise close to bedtime may worsen symptoms acutely.
Reduce triggers: Reduce or eliminate caffeine and alcohol, particularly in the evening. Review all medications with a prescriber.
Warm baths and massage: Provide temporary symptomatic relief.
Mental engagement during inactivity: Keeping the mind engaged (mental tasks, fidgeting devices) during unavoidable inactivity (long journeys, cinemas) can reduce symptom severity.

Pharmacological treatment for moderate to severe RLS

When non-pharmacological measures and iron supplementation are insufficient:

Alpha-2-delta ligands (preferred for chronic daily use):

Pregabalin and gabapentin — increasingly preferred over dopamine agonists for chronic daily RLS because of lower augmentation risk; also treat associated insomnia and anxiety
Side effects include dizziness and sedation, particularly at initiation

Dopaminergic agents:

Pramipexole and ropinirole (dopamine agonists) — effective for reducing RLS severity; risk of augmentation (worsening of symptoms over time, earlier onset, spread to arms) with long-term use at higher doses
Levodopa — effective for intermittent RLS; high augmentation risk with daily use; rarely used as first-line now

Augmentation is the most important complication of dopaminergic therapy — occurring in 30–50% of patients over years. It manifests as earlier symptom onset, greater intensity, and spread to the arms. If suspected, dose reduction or switch to an alpha-2-delta ligand is recommended under specialist guidance.

Opioids: Low-dose oxycodone or buprenorphine — reserved for severe, refractory RLS under specialist supervision.

FAQ

Q: What is restless legs syndrome?
A: A neurological condition causing an urge to move the legs, accompanied by uncomfortable sensations that worsen at rest and in the evening and are partially relieved by movement. Caused primarily by central dopamine dysregulation, often with iron deficiency as a modifiable contributor.

Q: What causes it?
A: Primarily dopamine dysregulation. Iron deficiency is a major treatable cause — iron is required for dopamine synthesis. Genetic factors, pregnancy, kidney disease, and certain medications can also trigger or worsen RLS.

Q: How is it diagnosed?
A: Clinically, based on the four core criteria. Ferritin measurement is standard. No sleep study is required for the diagnosis itself, though one may be arranged for associated sleep disruption.

Q: Is it treatable?
A: Yes. Iron supplementation substantially improves RLS when ferritin is below 75 µg/L — the treatment target is higher than the conventional normal range. Dopaminergic medications and alpha-2-delta ligands are effective for moderate-severe cases.

Q: Does RLS cause Parkinson’s disease?
A: RLS and Parkinson’s share dopaminergic pathways and often co-occur. However, the vast majority of people with RLS do not develop Parkinson’s disease. They are related but distinct conditions.