What is paradoxical post-arousal hypersynchrony?

Paradoxical Post-Arousal Hypersynchrony (PAH)

Paradoxical post-arousal hypersynchrony (PAH) is an electroencephalographic (EEG) pattern characterized by an abrupt shift to slower frequencies following arousal from sleep, appearing as clusters of slow waves that can be mistaken for paroxysmal activity. 1

Definition and Characteristics

• PAH manifests as an atypical arousal pattern where, instead of the expected faster EEG frequencies following arousal, there is a paradoxical shift to slower, high-amplitude waves 1
• This pattern appears as generalized, paroxysmal, synchronic, symmetrical, slow, high-voltage waves lasting 2-8 seconds 2
• PAH occurs predominantly during non-rapid eye movement (NREM) sleep and is not observed during rapid eye movement (REM) sleep 1
• The pattern is more prevalent during the first sleep cycle and the first half of the sleep period 1

Prevalence and Clinical Significance

• PAH is relatively common in healthy young adults, with studies showing it occurs in approximately 93% of healthy young participants (28 out of 30) 1
• It appears to be more frequent in children with learning disabilities (35.38%) compared to children without learning disabilities (4%) 2
• The number of PAH episodes correlates with the number of arousals and arousal indices 1
• PAH may be affected by sleep homeostasis processes, as it occurs more frequently in states with high prevalence of slow-wave sleep 1

Physiological Mechanisms

• PAH may function to suppress cortical arousal during NREM sleep, potentially serving as a protective mechanism against full awakening 1
• The pattern appears to be related to the sleep homeostasis process, as it occurs more frequently during periods with high slow-wave sleep percentage 1
• PAH may represent a transitional state in the complex interplay between arousal and sleep maintenance systems in the brain 1, 3

Clinical and Diagnostic Implications

• PAH should be distinguished from epileptiform activity, as it can be mistaken for paroxysmal clinical activity, especially in children 2
• Hypersynchronous delta activity and sudden arousals from slow-wave sleep are common findings in patients with sleep disorders like obstructive sleep apnea, even without histories of parasomnias 4
• These EEG patterns have low specificity for NREM parasomnias and should not be used alone for objective confirmation of parasomnias in clinical or forensic evaluations 4

Relationship to Other Sleep Phenomena

• PAH differs from paradoxical insomnia (sleep state misperception), which is characterized by a complaint of severe insomnia that greatly exceeds objective evidence of sleep disturbance 5
• It is also distinct from REM sleep behavior disorder, which involves dream enactment behaviors due to lack of normal muscle atonia during REM sleep 5
• PAH represents one of many complex EEG patterns that can occur during transitions between sleep stages and during arousals 5

Clinical Considerations

• When interpreting sleep EEG, clinicians should be aware of PAH as a normal variant to avoid misdiagnosis of epileptiform activity 2
• The presence of PAH may provide insights into sleep homeostasis and arousal mechanisms, particularly in patients with sleep disorders 1
• Further research is needed to fully understand the clinical significance and neurophysiological basis of PAH in different patient populations 1, 2