What is the recommended outpatient workup for restless leg syndrome (RLS)?

Outpatient Workup for Restless Legs Syndrome

The recommended outpatient workup for Restless Legs Syndrome (RLS) should prioritize serum ferritin testing as the first-line laboratory evaluation, with additional testing for secondary causes including complete blood count, basic metabolic panel, and liver function tests. 1

Diagnostic Criteria

RLS diagnosis is based on four essential clinical criteria:

1. An urge to move the legs, usually accompanied by uncomfortable sensations
2. Symptoms begin or worsen during periods of rest or inactivity
3. Symptoms are partially or totally relieved by movement
4. Symptoms worsen in the evening or night (circadian pattern)

These criteria should be assessed through detailed questioning about the nature, timing, and relieving factors of symptoms 1, 2.

Laboratory Evaluation

The primary laboratory workup should include:

• Serum ferritin level - Most important test, with values <50 ng/mL consistent with RLS diagnosis and indicating need for iron supplementation 1
• Iron studies - Including transferrin saturation (<20% suggests iron deficiency) 1
• Complete blood count - To evaluate for anemia 1
• Basic metabolic panel - To assess renal function (renal disease is a common secondary cause) 1
• Liver function tests - To rule out liver disorders 1
• HbA1c - To evaluate for diabetes 1
• Thyroid function tests - To rule out thyroid disorders 1
• Urine albumin:creatinine ratio - To assess for kidney disease 1

Evaluation for Secondary Causes

Secondary causes of RLS that should be investigated include:

• Iron deficiency (most common and treatable cause)
• Renal disease/chronic kidney disease
• Diabetes mellitus
• Pregnancy (pregnancy test when applicable)
• Medication side effects (particularly antidepressants, antihistamines, antipsychotics)
• Peripheral neuropathy
• Thyroid disorders 1, 3

Advanced Testing

• Polysomnography - Not routinely indicated but should be considered when:
  • Sleep apnea is suspected
  • Diagnosis is uncertain
  • Confirmation of periodic limb movements during sleep is needed 1

Diagnostic Instruments

Several validated diagnostic instruments can be used to confirm RLS diagnosis:

• RLS Diagnostic Index (RLS-DI) - A 10-item questionnaire probing essential diagnostic features and associated criteria 2
• Cambridge-Hopkins Diagnostic Questionnaire (CH-RLSq) - A self-completed 13-question tool that probes the 4 basic criteria and excludes RLS mimics 2

Important Clinical Considerations

• Distinguish RLS from mimics such as positional discomfort, leg cramps, and peripheral neuropathy 2, 1
• Assess symptom severity using validated scales to guide treatment decisions 2
• Document impact on sleep quality and daily functioning 2, 1
• Review current medications that may exacerbate RLS (antidepressants, antihistamines, antipsychotics) 1
• Obtain family history (genetic predisposition is common) 3

Common Pitfalls to Avoid

1. Overlooking iron deficiency - Always check ferritin levels, even in patients without anemia 1
2. Misdiagnosis - Failing to distinguish RLS from other conditions with similar symptoms (leg cramps, positional discomfort, neuropathy) 2, 1
3. Incomplete workup - Not evaluating for common secondary causes 1
4. Relying solely on subjective reports - Consider using validated diagnostic instruments 2
5. Neglecting impact assessment - Not evaluating the effect of RLS on sleep quality and daily functioning 2, 1

By following this systematic approach to RLS evaluation, clinicians can establish an accurate diagnosis and identify underlying causes, which will guide appropriate treatment decisions and improve patient outcomes.