Limb Movements Related to Respiratory Events on Polysomnography
Limb movements that occur during or immediately following respiratory events should not be counted as periodic limb movements on a polysomnogram according to the American Academy of Sleep Medicine (AASM) guidelines.
Rationale for Not Counting 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 should not be confused with true periodic limb movements that have a different pathophysiology 2.
Counting respiratory-related limb movements as PLMS could lead to overestimation of the periodic limb movement index (PLMI), potentially resulting in misdiagnosis and inappropriate treatment 3.
Proper Scoring of Periodic Limb Movements
For proper diagnosis of Periodic Limb Movement Disorder (PLMD), clinicians should use electromyography (EMG) during polysomnography to measure PLMs during confirmed sleep periods only, excluding those associated with respiratory events 1, 4.
The diagnosis of PLMD requires frequent PLMS (>15 events/hour in adults, >5 events/hour in children) and clinically significant sleep disturbance not better explained by another disorder 1.
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 1.
Clinical Implications and Potential Pitfalls
Misinterpretation of respiratory-related limb movements as PLMS can lead to incorrect diagnosis and treatment. In some cases, patients have been misdiagnosed with sleep-disordered breathing when the primary issue was actually periodic limb movement disorder 3.
Research has shown that up to 85% of respiratory events could be associated with central hypoventilation following periodic limb movement-associated EEG arousal, highlighting the complex relationship between these phenomena 3.
Failure to distinguish between respiratory-related limb movements and true PLMS can result in inappropriate treatment decisions and poor patient outcomes 4, 3.
Technical Considerations
Modern polysomnography systems include automated software for detecting and analyzing limb movements, but these should be used with caution and validated against manual scoring 5.
When evaluating limb movements, technicians should carefully examine the temporal relationship between respiratory events and limb movements to ensure proper classification 4, 5.
The correlation between manual and computerized scoring of limb movements can be high when using validated systems (correlation coefficients 0.751-0.996), but human oversight remains important 5.
Best Practices for Polysomnography Interpretation
Recording and scoring of leg movements must be an integral part of polysomnographic evaluations to avoid misinterpretation of sleep disorders 3.
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 4.
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, 4.