What is the purpose and procedure of polysomnography (PSG) in diagnosing sleep disorders?

Polysomnography: Purpose and Procedure

Polysomnography (PSG) is the gold standard diagnostic test for sleep disorders, involving electrographic recording of multiple simultaneous physiologic variables during sleep to objectively diagnose conditions like obstructive sleep apnea, narcolepsy, parasomnias, and periodic limb movement disorder. 1

Core Purpose

PSG serves as the definitive diagnostic tool for:

• Sleep-related breathing disorders (obstructive sleep apnea, central sleep apnea, sleep-related hypoventilation) where it is routinely indicated 1, 2, 3
• Narcolepsy evaluation when combined with multiple sleep latency testing 2, 3
• Violent or injurious parasomnias including REM sleep behavior disorder, which predicts neurodegenerative disorders 4, 2
• Periodic limb movement disorder when clinical suspicion is strong 2, 3
• Sleep-related epilepsy when seizures are suspected to occur during sleep 2, 3

Physiologic Parameters Measured

PSG simultaneously records the following parameters during sleep 1:

• Sleep staging via electroencephalogram (EEG)
• Eye movements via electro-oculogram (EOG)
• Muscle tone via electromyogram (EMG)
• Gas exchange including oxygen saturation via pulse oximetry
• Respiratory effort to detect breathing abnormalities
• Airflow to identify apneas and hypopneas
• Snoring intensity and frequency
• Body position during sleep
• Limb movements to detect periodic movements
• Heart rhythm via electrocardiogram (ECG) 4, 3

Critical Scoring Requirements

For obstructive sleep apnea diagnosis, PSG must include arousal-based scoring of respiratory events, as arousals—not hypoxemia alone—better predict hypersomnia and neurocognitive symptoms. 1

• Score respiratory effort-related arousals (RERAs) as sequences of breaths ≥10 seconds with increasing respiratory effort or flattening of nasal pressure waveform leading to arousal 1
• An apnea-hypopnea index (AHI) ≥5 events/hour using arousal-based criteria, or respiratory disturbance index (RDI) ≥5 events/hour, warrants treatment in symptomatic patients 1
• Omitting arousal-based scoring leads to misdiagnosis, misclassification of severity, or failure to identify OSA entirely 1

When PSG is Mandatory vs. Alternative Testing

PSG is required (not optional) in the following scenarios 1:

• Patients with significant cardiorespiratory disease
• Suspected respiratory muscle weakness from neuromuscular conditions
• Awake hypoventilation or suspected sleep-related hypoventilation
• Chronic opioid medication use
• History of stroke
• Severe insomnia
• When home sleep apnea testing (HSAT) is negative, inconclusive, or technically inadequate 1

HSAT may be used as an alternative only in uncomplicated adult patients with high pretest probability of moderate to severe OSA, absent the above comorbidities 1

Special Populations Requiring PSG

Children Prior to Tonsillectomy

Children with sleep-disordered breathing require PSG before tonsillectomy if they have 1:

• Obesity, Down syndrome, craniofacial abnormalities, neuromuscular disorders, sickle cell disease, or mucopolysaccharidoses
• Uncertain surgical indication or discordance between tonsillar size and reported symptom severity
• Laboratory-based PSG (not home testing) should be obtained when available 1

Post-operative risk stratification: Children with severe OSA (AHI ≥10 events/hour or oxygen saturation nadir <80%) or age <3 years require inpatient overnight monitoring after tonsillectomy 1

Testing Environment

Laboratory-based PSG with continuous technician attendance is preferred over portable monitoring for most diagnostic scenarios 1

• Portable monitoring (Level III-IV devices) lacks EEG data, preventing arousal-based respiratory event identification 1
• In-laboratory PSG allows real-time troubleshooting, ensures data quality, and enables split-night protocols (diagnostic study followed by CPAP titration in same night) when clinically appropriate 1

Common Pitfalls to Avoid

Do not use clinical tools, questionnaires, or prediction algorithms alone to diagnose OSA—they have low accuracy and high certainty that harms outweigh benefits 1

Do not perform PSG routinely for 2, 5:

• Chronic lung disease diagnosis (though PSG may assess sleep-related complications)
• Typical, uncomplicated, noninjurious parasomnias with clear clinical diagnosis
• Restless legs syndrome diagnosis (clinical diagnosis)
• Circadian rhythm sleep disorders
• Routine evaluation of transient or chronic insomnia without suspected sleep-related breathing disorder or periodic limb movements 5

Do perform repeat PSG when initial study is negative but clinical suspicion for OSA remains high 1

Clinical Pathway Requirements

PSG must occur within a comprehensive sleep evaluation by a board-certified sleep medicine physician 1

This ensures:

• Appropriate patient selection avoiding overutilization
• Identification of comorbid medical, psychiatric, and other sleep disorders
• Accurate data collection with trained technologists
• Effective treatment planning and follow-up 1

Communicate PSG results to anesthesiologists before surgical procedures in patients with sleep-disordered breathing to optimize perioperative safety 1