What is the approach to evaluating a patient for restless leg syndrome?

Evaluation of Restless Legs Syndrome

Diagnose RLS clinically using four essential criteria from the patient's history, perform a thorough neurologic examination to exclude mimics, and obtain serum ferritin (with transferrin saturation if available) as the only required laboratory test. 1

Clinical Diagnostic Criteria

The diagnosis is established by asking four specific questions—all must be answered "yes" for RLS diagnosis 1:

1. Is there an urge to move the legs accompanied by uncomfortable or unpleasant sensations? 1
2. Do symptoms begin or worsen during rest or inactivity (sitting/lying)? 1
3. Are symptoms partially or totally relieved by movement (walking/stretching) for as long as the activity continues? 1
4. Do symptoms worsen or only occur in the evening or night? 1

No polysomnography or periodic limb movement studies are needed for routine diagnosis—these should be reserved only for uncertain cases or research settings. 2

Physical Examination

The neurologic examination is typically unremarkable in primary RLS, but a thorough exam is essential to identify secondary causes and exclude mimics. 1

Focus your examination on 1:

• Peripheral neuropathy signs: Assess distal sensation, reflexes, and proprioception
• Radiculopathy indicators: Straight leg raise, dermatomal patterns
• Vascular disease: Palpate pulses (dorsalis pedis, posterior tibial, popliteal, femoral), check for bruits, assess for dependent rubor or elevation pallor
• Joint abnormalities: Examine for arthritis, which can mimic RLS but shows joint-specific tenderness and lacks circadian pattern

Laboratory Testing

Check serum ferritin in all patients—this is the only essential laboratory test. 1, 2

Iron Studies Protocol 2:

• Draw in the morning after avoiding iron supplements/foods for ≥24 hours (ferritin has diurnal variation and recent intake falsely elevates results)
• Obtain both ferritin AND transferrin saturation (ferritin alone can be falsely elevated by inflammation)
• RLS-specific thresholds differ from general population: Supplement if ferritin ≤75 ng/mL OR transferrin saturation <20%
• Values <50 ng/mL are consistent with RLS diagnosis and indicate need for iron supplementation 1

Additional Testing to Consider 2:

• CBC: Reasonable to assess for iron-deficiency anemia
• Renal function/electrolytes: Identify chronic kidney disease (secondary RLS cause)
• TSH: Screen for thyroid dysfunction
• HbA1c: Screen for diabetes (associated with peripheral neuropathy)
• Pregnancy test: Where applicable (pregnancy is a known secondary cause)

Differential Diagnosis

A careful history usually distinguishes RLS from mimics—the key is the circadian pattern and relief with movement. 1

Conditions to exclude 1, 2:

• Peripheral neuropathy: Pain/numbness without circadian pattern, abnormal neurologic exam
• Vascular disease (claudication): Pain with walking (opposite of RLS), diminished pulses
• Neuroleptic-induced akathisia: Urge to move entire body, no uncomfortable leg sensations, medication history
• Arthritis: Joint-localized pain, no circadian pattern, abnormal joint exam
• Radiculopathy: Dermatomal distribution, positive straight leg raise

Special Population: Cognitively Impaired Patients

For patients unable to describe symptoms, observe for behavioral signs. 1

Essential criteria for diagnosis in cognitively impaired 1:

1. Signs of leg discomfort: Rubbing/kneading legs, groaning while holding lower extremities
2. Excessive motor activity: Pacing, fidgeting, repetitive kicking, tossing in bed, foot tapping, rubbing feet together
3. Signs present exclusively or worse during inactivity
4. Signs diminished with activity
5. Criteria 1 and 2 occur only in evening/night or worse at those times

Critical Pitfalls to Avoid

Without proper differential diagnosis, 16% of patients will be misclassified as having RLS if you only assess the four symptom criteria without excluding mimics. 2

• Don't skip the neurologic exam: An abnormal exam suggests peripheral neuropathy, radiculopathy, or vascular disease rather than primary RLS 1, 2
• Don't use general population iron thresholds: RLS requires supplementation at ferritin ≤75 ng/mL, not the typical <30 ng/mL cutoff 2
• Don't check ferritin without proper preparation: Morning draw after 24-hour iron avoidance is essential for accuracy 2
• Don't order polysomnography routinely: This is not part of standard diagnostic workup 2