What is the leg movement that needs to be marked during a Polysomnography (PSG)?

Leg Movements to Mark During Polysomnography (PSG)

During polysomnography, periodic limb movements (PLM) should be marked when they consist of repetitive, highly stereotyped movements characterized by dorsiflexion of the ankle and extension of the big toe, sometimes with flexion of the knee and hip, each lasting approximately 2-4 seconds and occurring roughly every 20-40 seconds. 1, 2

Characteristics of Periodic Limb Movements to Mark

• Movement pattern: Rhythmical extensions of the big toe and dorsiflexions of the ankle with occasional flexions of the knee and hip 1
• Duration: Each movement lasts approximately 2-4 seconds 1
• Frequency: Typically occurs about once every 20-40 seconds 1
• Timing: Usually occur predominantly during the first part of the night 1
• Sleep stage: Should be counted during NREM sleep, not during REM sleep 2

Diagnostic Criteria for PLMD

For a diagnosis of Periodic Limb Movement Disorder (PLMD), the following criteria must be met:

1. Polysomnography demonstrates repetitive, highly stereotyped limb movements 1
2. The PLMS Index exceeds 15 per hour in adults (>5 per hour in children) 1, 2
3. There is clinical sleep disturbance or a complaint of daytime fatigue 1
4. The PLMS are not better explained by another current sleep disorder, medical or neurologic disorder, mental disorder, medication use, or a substance use disorder 1

Technical Considerations for PLM Marking

• Gold standard: Electromyography (EMG) during PSG is the required method for accurate PLM detection 1, 3
• Actigraphy warning: Actigraphy should not be used in place of EMG for the diagnosis of PLMD as it produces unreliable estimates of periodic limb movements 1
• Automated detection: While automated PLM detection software exists and shows high correlation with manual scoring (r²=0.94), manual review remains important for accurate diagnosis 4
• Respiratory event exclusion: Leg movements occurring within 5 seconds of respiratory events should be excluded from PLM counts as they may be secondary to sleep disordered breathing 4

Clinical Significance

• PLM may cause brief awakenings or arousals from sleep, of which the individual may or may not be aware 1
• The presence of PLM supports but is not sufficient for the diagnosis of Restless Legs Syndrome (RLS) 1
• PLM are associated with cardiovascular changes including elevations in heart rate and blood pressure 2
• If PLM are present without clinical sleep disturbance, they can be reported as a polysomnographic finding, but criteria are not met for a diagnosis of PLMD 1

Common Pitfalls in PLM Assessment

• Misclassification: Failing to distinguish between PLM and other movements during sleep
• REM inclusion: Incorrectly counting PLM during REM sleep, which should be excluded 2
• Respiratory-related movements: Not excluding leg movements associated with respiratory events
• Diagnostic confusion: Mistaking PLM for myoclonic jerks (PLM are slower than true myoclonic movements) 5
• Overdiagnosis: Not recognizing that most individuals with PLMS do not have PLMD, which is a diagnosis of exclusion 2