What findings are observed on polysomnography and electroencephalogram in a patient with restless legs syndrome?

Polysomnographic and EEG Findings in Restless Legs Syndrome

Sleep studies in RLS patients show periodic limb movements during sleep (PLMS) as brief, recurrent lower extremity movements lasting 0.5-10 seconds occurring every 15-30 seconds, while EEG demonstrates arousals associated with these movements, though the movements invariably correlate with elevations in heart rate and blood pressure. 1

Key Polysomnographic Findings

Periodic Limb Movements Characteristics

• PLMS are detected as brief (0.5-10 seconds), recurrent movements of the lower extremities occurring roughly every 15-30 seconds 1
• These movements are particularly concentrated during the first 4 hours of the sleep period 1
• PLMS demonstrate high night-to-night variability in both adults and children 1
• The movements consist of rhythmic extensions of the big toe and dorsiflexions of the ankle, occasionally with knee and hip flexions 1, 2
• Each individual movement lasts approximately 2-4 seconds 1, 2

Sleep Architecture Disruption

• Total sleep time and sleep efficiency are significantly reduced compared to healthy controls 3
• Wake time after sleep onset is increased 3
• Stage N1 sleep percentage is increased while stage N2 and REM sleep percentages are decreased 3
• REM latency is prolonged 3
• Stage shifts per hour are increased, reflecting sleep fragmentation 3
• Arousal index is significantly elevated 3

EEG Findings

Arousal Patterns

• PLMS can be associated with electroencephalogram arousals, though not all movements trigger visible EEG changes 1
• Significantly fewer PLMS are associated with microarousals in RBD patients compared to primary RLS, suggesting variable cortical reactivity 4
• The arousal index is consistently elevated in RLS patients compared to healthy controls 3

State-Dependent Variations

• PLMS are more frequent during non-REM sleep compared to REM sleep 3
• Movement intervals are shorter during wakefulness and increase progressively from stage 1 to stage 2 sleep, and to slow wave sleep 5
• During REM sleep, movement duration is shorter and frequency is lowest, likely due to spinal motoneuron inhibition 5
• REM sleep intervals return to values similar to stage 1 sleep 5

Autonomic Findings

Cardiovascular Changes

• PLMS are invariably associated with elevations in heart rate and blood pressure 1
• A transient tachycardia followed by bradycardia occurs in close association with every PLMS 4
• The amplitude of cardiac activation may be reduced in certain conditions like RBD compared to primary RLS 4

Diagnostic Thresholds

PLMS Index Criteria

• A PLMS index >15 events per hour in adults is considered abnormal for PLMD diagnosis 1
• In children, the threshold is >5 events per hour 1
• Up to 90% of RLS patients demonstrate PLMS on polysomnography 1, 2

Important Caveats

• PLMS are neither necessary nor sufficient to diagnose RLS—the diagnosis remains clinical 1
• PLMS can occur with other sleep disorders including untreated obstructive sleep apnea, REM sleep behavior disorder, and narcolepsy 1
• PLMS are also common in patients taking antidepressants 1
• The periodicity index may be a more sensitive and specific marker of RLS than the PLMS index alone 3

Clinical Significance

The presence of PLMS without clinical sleep disturbance does not require treatment and can be reported as a polysomnographic finding without meeting criteria for PLMD 1, 6. The combination of PLMS with sleep fragmentation, increased arousals, and autonomic activation explains the insomnia and daytime fatigue experienced by approximately 90% of RLS patients 1.