Can periodic limb movements (PLM) be counted during Rapid Eye Movement (REM) sleep?

Periodic Limb Movements During REM Sleep

Periodic limb movements (PLM) should not be counted during REM sleep according to standard American Academy of Sleep Medicine (AASM) diagnostic criteria, as they are primarily assessed during NREM sleep for the diagnosis of Periodic Limb Movement Disorder (PLMD). 1, 2

Rationale for Not Counting PLMs During REM Sleep

• The AASM scoring manual does not include specific rules for counting periodic limb movements during REM sleep 1
• PLMs have different characteristics and clinical significance during REM versus NREM sleep:
  • PLMs occur much less frequently during REM sleep
  • During REM sleep, normal muscle atonia makes PLM detection more difficult
  • PLMs that do occur during REM may represent different physiological phenomena than those in NREM sleep

Diagnostic Criteria for PLMD

For proper diagnosis of Periodic Limb Movement Disorder, the following criteria must be met:

• Frequency threshold: >15 events/hour in adults or >5 events/hour in children 2
• PLMs must be associated with a clinically significant sleep disturbance or daytime dysfunction
• Other sleep disorders that could explain the symptoms must be excluded (especially RLS, narcolepsy, REM sleep behavior disorder, and sleep-related breathing disorders) 2
• PLMs are characterized by brief, recurrent movements of the lower extremities occurring roughly every 15-30 seconds, particularly during the first 4 hours of sleep 2

Technical Considerations

When evaluating PLMs, several important technical factors should be considered:

• Standard PLM scoring uses amplitude criteria that significantly impact detection rates - studies show that counting without amplitude criteria results in significantly higher PLM counts in both NREM and REM sleep 3
• In one study, the PLMI in REM sleep was 11.5±15.1 with amplitude criteria versus 25.7±35.4 without amplitude criteria (p=0.001) 3
• Actigraphy is not recommended as a replacement for EMG during polysomnography for PLM assessment, as it produces unreliable estimates of periodic limb movements 1

Clinical Implications

Understanding the relationship between PLMs and sleep stages has important clinical implications:

• 92% of all PLMs in NREM sleep occur during Cyclic Alternating Pattern (CAP), with 96% associated with phase A of CAP 4
• PLMs may sometimes mimic REM sleep behavior disorder, but video-polysomnography can differentiate between these conditions 5
• When evaluating PLMs, it's essential to consider their relationship to arousals and sleep fragmentation, which is primarily assessed during NREM sleep

Conclusion

While PLMs can technically be observed during REM sleep, they are not typically counted as part of standard diagnostic criteria for PLMD. The focus remains on NREM-related PLMs for diagnostic purposes, as outlined in the AASM scoring manual. Researchers continue to study the relationship between PLMs in different sleep stages, but current clinical practice does not emphasize the counting of PLMs during REM sleep for diagnostic purposes.