What is the difference between polygraphy and polysomnography (PSG) in diagnosing sleep disorders?

Polygraphy vs. Polysomnography: Key Differences in Sleep Disorder Diagnostics

Polysomnography (PSG) is the gold standard for diagnosing sleep disorders, providing comprehensive physiological monitoring, while polygraphy is a limited alternative that only records respiratory parameters without sleep staging and is appropriate only for uncomplicated patients with high pre-test probability of obstructive sleep apnea. 1

Fundamental Differences

Polysomnography (PSG)

• Definition: Comprehensive electrographic recording of simultaneous physiologic variables during sleep 1
• Parameters measured:
  • Sleep staging via electroencephalogram (EEG)
  • Eye movements (electro-oculogram)
  • Muscle tone (electromyogram)
  • Gas exchange and respiratory effort
  • Airflow and snoring
  • Body position
  • Limb movement
  • Heart rhythm (electrocardiogram)
• Setting: Typically performed in a sleep laboratory with continuous attendance by a technician 1
• Gold standard: Considered the definitive test for objectively assessing sleep disorders 1, 2

Polygraphy

• Definition: Limited channel recording focusing primarily on respiratory parameters
• Parameters measured:
  • Respiratory effort
  • Airflow
  • Oxygen saturation
  • Heart rate
  • Body position (sometimes)
• Setting: Often performed as a home sleep apnea test (HSAT)
• Limitations: Cannot detect sleep stages, arousals without desaturation, or determine total sleep time 1

Clinical Applications

When to Use Polysomnography

1. Complex sleep disorders:

   • Suspected narcolepsy (followed by multiple sleep latency test) 3, 4
   • Parasomnias, especially violent or potentially injurious behaviors 4
   • Sleep-related epilepsy 4
   • Periodic limb movement disorder 4

2. High-risk populations:

   • Children with sleep-disordered breathing and complex medical conditions (obesity, Down syndrome, craniofacial abnormalities, neuromuscular disorders) 1
   • Patients with comorbidities (neuromuscular disorders, heart failure, COPD, stroke) 2
   • Suspected central sleep apnea or sleep-related hypoventilation 2, 5

3. Discordant clinical picture:

   • When there is discrepancy between tonsillar size and reported severity of sleep-disordered breathing 1
   • When the need for surgery is uncertain 1

When to Use Polygraphy

1. Uncomplicated adult patients:

   • High pre-test probability of moderate to severe obstructive sleep apnea 1
   • Absence of significant comorbidities 1, 5
   • No suspicion of other sleep disorders 1

2. Practical considerations:

   • When PSG cannot be performed (hospitalization, inability to leave home) 1
   • As part of home sleep apnea testing protocols 5

Diagnostic Accuracy and Limitations

Polysomnography Advantages

• Provides comprehensive sleep architecture information
• Can detect arousals even without oxygen desaturation
• Measures actual sleep time (not just recording time)
• Can detect REM-related events
• Can diagnose non-respiratory sleep disorders 1, 2

Polygraphy Limitations

• Cannot detect events that result in arousal without desaturation
• Cannot determine how long the patient actually slept
• Cannot detect carbon dioxide elevation
• Cannot identify flow limitation without discrete desaturation
• Cannot determine if REM sleep was achieved 1
• May underestimate the severity of sleep apnea 1

Clinical Decision-Making Algorithm

1. Initial assessment: Evaluate for risk factors and symptoms of sleep disorders

2. Choose diagnostic test:

   • Use PSG if:

     • Patient has comorbid conditions (cardiac, pulmonary, neurological)
     • Suspicion of non-respiratory sleep disorders
     • Children with complex medical conditions
     • Need for precise severity assessment

   • Consider polygraphy if:

     • High pre-test probability of moderate-severe OSA
     • Adult patient without significant comorbidities
     • No suspicion of other sleep disorders
     • PSG is not feasible or available

3. Follow-up testing:

   • If polygraphy is inconclusive or negative despite high clinical suspicion, proceed to PSG 1

Important Caveats

• Polygraphy should only be performed within the context of a comprehensive sleep evaluation by a trained expert in sleep medicine 1
• The accuracy of polygraphy has not been validated in patients with severe insomnia or those at risk for central sleep apnea or hypoventilation 1
• Laboratory-based PSG should be obtained when available for children requiring sleep assessment prior to tonsillectomy 1
• Clinical judgment remains essential in determining the appropriate diagnostic approach for each patient 6