Can sleep apnea cause narcolepsy?

Sleep Apnea and Narcolepsy: Relationship and Diagnostic Considerations

Sleep apnea does not cause narcolepsy, but it can coexist with narcolepsy and must be adequately treated before a diagnosis of narcolepsy can be established. 1

Understanding the Relationship Between Sleep Apnea and Narcolepsy

Sleep apnea and narcolepsy are distinct sleep disorders with different underlying mechanisms:

• Sleep Apnea: A disorder characterized by repeated episodes of complete or partial upper airway obstruction during sleep, leading to disrupted nocturnal sleep and subsequent daytime sleepiness.

• Narcolepsy: A hypersomnia of central origin characterized by excessive daytime sleepiness and often accompanied by symptoms of REM sleep dyscontrol such as cataplexy, sleep paralysis, and hypnagogic hallucinations.

Key Diagnostic Considerations

When evaluating a patient with excessive daytime sleepiness:

1. Rule out sleep apnea first: The American Academy of Sleep Medicine guidelines emphasize that sleep apnea must be adequately treated before considering an independent diagnosis of hypersomnia, including narcolepsy 1.

2. Diagnostic testing:

   • Nocturnal polysomnography (NPSG) followed by multiple sleep latency test (MSLT)
   • Diagnostic criteria for narcolepsy: mean sleep latency <8 minutes AND ≥2 sleep-onset REM periods 2
   • CSF hypocretin-1 measurement (levels <110 pg/mL diagnostic for narcolepsy type 1) 2

Clinical Implications of Coexisting Conditions

The coexistence of sleep apnea and narcolepsy is not uncommon:

• Studies have found that 24.8% to 51.4% of narcolepsy patients also have obstructive sleep apnea 3
• This association can complicate diagnosis and management:
  • Sleep apnea can mask narcolepsy symptoms
  • Diagnosis of narcolepsy may be delayed by several years (average 6.1±7.8 years) in patients initially diagnosed with only OSA 4
  • Treatment with CPAP alone does not usually improve excessive daytime sleepiness in narcoleptic patients with OSA 4

Diagnostic Algorithm for Patients with Excessive Daytime Sleepiness

1. Screen for sleep apnea with polysomnography
2. Treat sleep apnea if present (typically with CPAP)
3. Reassess sleepiness after adequate treatment of sleep apnea
4. If excessive sleepiness persists, evaluate for narcolepsy with MSLT and consider:
   • Presence of cataplexy (pathognomonic for narcolepsy type 1)
   • Other narcolepsy symptoms (sleep paralysis, hypnagogic hallucinations)
   • CSF hypocretin levels when available

Common Pitfalls to Avoid

• Misattribution of symptoms: Attributing all sleepiness to sleep apnea when narcolepsy is also present
• Incomplete treatment evaluation: Failing to reassess sleepiness after adequate CPAP therapy
• Overlooking cataplexy: Not specifically asking about cataplexy in patients with OSA and persistent sleepiness 4
• Assuming improvement with CPAP alone: Studies show that in patients with both conditions, CPAP does not usually improve excessive daytime sleepiness 4

The association between these disorders may be related to the involvement of orexin (hypocretin) in hypercapnic-hypoxic responses, as a deficit of orexin may promote obstructive events during sleep 3. However, they remain distinct disorders with different underlying pathophysiologies.