When should a limb movement be considered part of a respiratory event?

Limb Movements Associated with Respiratory Events

A limb movement should be considered part of a respiratory event when it occurs in direct temporal relationship with the respiratory event, specifically when the limb movement is triggered as a physiological response to oxygen desaturation or arousal caused by the respiratory event. 1

Diagnostic Criteria for Respiratory-Related Limb Movements

• The American Academy of Sleep Medicine (AASM) guidelines specify that limb movements associated with respiratory events should not be counted as periodic limb movements of sleep (PLMS) to avoid misdiagnosis and ensure accurate assessment of sleep disorders 1
• Respiratory events can trigger limb movements as a physiological response to oxygen desaturation or arousal, which have a different pathophysiology than true periodic limb movements 1
• For proper diagnosis of Periodic Limb Movement Disorder (PLMD), clinicians should exclude limb movements associated with respiratory events from the PLMS count 2

Distinguishing Features of Respiratory-Related vs. True Periodic Limb Movements

• True PLMS are specifically defined as brief (0.5-10 seconds), recurrent movements of the lower extremities that occur approximately every 15-30 seconds during sleep, particularly during the first 4 hours of the sleep period 2
• PLMS diagnosis requires frequent movements (>15 events/hour in adults, >5 events/hour in children) and clinically significant sleep disturbance not better explained by another disorder 2
• Respiratory-related limb movements occur in direct temporal relationship to respiratory events rather than in the periodic pattern characteristic of PLMS 1

Clinical Implications and Best Practices

• Failure to distinguish between respiratory-related limb movements and true PLMS can result in inappropriate treatment decisions and poor patient outcomes 1
• The AASM recommends interpreting polysomnography according to standardized criteria, with careful attention to the relationship between respiratory events and other phenomena such as limb movements 1
• For research purposes and clinical trials, it is particularly important to adhere strictly to the AASM guidelines regarding the exclusion of respiratory-related limb movements from PLMS counts to ensure consistency and comparability of results 1

Physiological Basis for Respiratory-Limb Movement Relationship

• Breathing constantly adapts to environmental, metabolic, or behavioral changes by responding to different sensory information, including afferent feedback from muscles 3
• Afferent sensory information from rhythmically moving limbs has been shown to play an essential role in breathing regulation 3
• Fatigue-induced activation of limb muscle metaboreceptors served by group IV fine afferent fibers may impact respiratory effort perception, demonstrating the bidirectional relationship between limb muscle activity and respiratory function 4

Common Pitfalls in Scoring

• Misidentifying respiratory-related limb movements as PLMS can lead to overdiagnosis of PLMD 1
• Failing to recognize the temporal relationship between respiratory events and limb movements may result in inappropriate treatment targeting limb movements rather than the underlying respiratory disorder 1
• The variability of the periodic limb movements of sleep index (PLMSI) night-to-night in both adults and children can further complicate accurate diagnosis if not properly accounted for 2

By carefully examining the temporal relationship between limb movements and respiratory events during polysomnography, clinicians can accurately distinguish between true periodic limb movements and those that should be considered part of respiratory events, leading to more appropriate diagnosis and treatment decisions.