What is the diagnostic approach for restless legs syndrome (RLS)?

Diagnostic Approach for Restless Legs Syndrome

The diagnosis of Restless Legs Syndrome (RLS) is primarily clinical, based on fulfilling all four essential diagnostic criteria established by the International Restless Legs Syndrome Study Group. 1

Essential Diagnostic Criteria

All of the following four criteria must be met for a diagnosis of RLS:

1. An urge to move the legs usually accompanied by or felt to be caused by uncomfortable and unpleasant sensations in the legs
2. Symptoms begin or worsen during periods of rest or inactivity such as lying down or sitting
3. Symptoms are partially or totally relieved by movement such as walking or stretching, at least as long as the activity continues
4. Symptoms occur only in the evening/night or are worse during these times compared to daytime 1, 2

Clinical Assessment

When evaluating a patient with suspected RLS, follow this structured approach:

1. Detailed History

• Document the exact nature of sensations (patients may describe them as creeping, crawling, pulling, itching, burning, or aching) 3
• Establish the circadian pattern (worsening in evening/night)
• Determine if symptoms are relieved by movement
• Assess impact on sleep and quality of life
• Identify any family history of similar symptoms (supportive feature)
• Review medication history for potential exacerbating drugs (e.g., antidepressants, antihistamines)

2. Physical Examination

• Perform a thorough neurological examination (typically normal in primary RLS)
• Focus on identifying signs of peripheral neuropathy or radiculopathy that could suggest secondary RLS 1

3. Laboratory Testing

• Serum ferritin level is essential - values less than 50 ng/mL are consistent with a diagnosis of RLS and suggest the need for iron supplementation 1, 2
• Consider additional tests to rule out secondary causes:
  • Complete blood count
  • Basic metabolic panel
  • Liver function tests
  • Thyroid function tests
  • HbA1c
  • Urine albumin:creatinine ratio 2

4. Diagnostic Tools

For cases where the diagnosis remains uncertain, validated diagnostic instruments can be used:

• RLS Diagnostic Index (RLS-DI) - has excellent diagnostic attributes with sensitivity of 93% and specificity of 98.9% 1
• Cambridge-Hopkins Diagnostic Questionnaire (CH-RLSq) - a self-completed questionnaire that probes the 4 basic criteria and excludes RLS mimics 1, 2
• Hening Telephone Diagnostic Interview (HTDI) - useful for telephone-based diagnosis with excellent sensitivity and specificity 1

Differential Diagnosis

It's crucial to distinguish RLS from conditions that may mimic it:

• Peripheral neuropathies - typically have sensory symptoms that are constant rather than circadian
• Vascular disease/intermittent claudication - pain triggered by exercise, not rest
• Nocturnal leg cramps - characterized by sudden, painful muscle contractions
• Neuroleptic-induced akathisia - not typically worse at night and involves generalized restlessness
• Positional discomfort - relieved by changing position rather than continued movement
• Arthritis - pain typically related to specific joints and movements 1, 4

Special Considerations

Diagnosis in Cognitively Impaired Patients

For cognitively impaired individuals who cannot clearly articulate symptoms, look for:

1. Signs of leg discomfort (rubbing/kneading legs, groaning while holding legs)
2. Excessive motor activity in lower extremities (pacing, fidgeting, repetitive kicking)
3. Signs of leg discomfort worse during periods of inactivity
4. Signs of leg discomfort diminished with activity
5. Symptoms occurring only in evening/night or worse at those times 1

Polysomnography

While not required for diagnosis, polysomnography may be considered when:

• Sleep apnea is suspected
• Diagnosis is uncertain
• Symptoms are refractory to treatment 2
• To document periodic limb movements during sleep (PLMS), which occur in 80-90% of RLS patients 3, 5

Pitfalls to Avoid

1. Overlooking iron deficiency - Always check ferritin levels, as iron deficiency is a common and treatable cause of RLS
2. Misdiagnosing mimics - Ensure all four essential criteria are met, not just leg discomfort
3. Neglecting medication review - Certain medications can cause or exacerbate RLS symptoms
4. Focusing only on sensory symptoms - The urge to move is the core feature, even if sensory symptoms are minimal
5. Missing secondary causes - Always consider conditions like renal failure, pregnancy, and neuropathies that can cause secondary RLS 3, 5

By following this systematic diagnostic approach and ensuring all four essential criteria are met, clinicians can accurately diagnose RLS and distinguish it from conditions with similar presentations.