Why is a sleep study recommended for a patient with polycythemia (a condition characterized by an increased red blood cell count) after a stroke?

Sleep Study for Polycythemia After Stroke: Understanding the Rationale

A sleep study is recommended for patients with polycythemia after stroke primarily to evaluate for sleep-disordered breathing, particularly obstructive sleep apnea (OSA), which is present in up to 40% of stroke patients and can contribute to both stroke risk and poor recovery outcomes. 1

Connection Between Sleep Disorders, Stroke, and Polycythemia

Sleep Disorders and Stroke

• Sleep disorders, particularly OSA, are both risk factors for stroke and common consequences of stroke, with prevalence rates of 30-70% in post-stroke patients 2
• The American Heart Association/American Stroke Association recognizes that sleep-disordered breathing has been identified as an independent risk factor for stroke and may contribute to poststroke fatigue and affect stroke recovery 1
• Three main sleep disorders among stroke survivors are sleep apnea, nighttime sleep disturbances, and excessive daytime sleepiness 1

Sleep Apnea and Polycythemia Connection

• OSA causes intermittent hypoxemia during sleep, which can trigger compensatory increases in red blood cell production, leading to secondary polycythemia 3
• The chronic intermittent hypoxia from untreated sleep apnea stimulates erythropoietin production, resulting in increased red blood cell mass 3
• Polycythemia itself can increase stroke risk through increased blood viscosity and impaired microcirculation 3

Impact of Sleep Disorders on Stroke Recovery

• Patients with stroke and concomitant sleep disorders show poorer functional outcomes than those without sleep disorders 4
• Meta-analysis shows that stroke patients with sleep disorders have:
  • Higher modified Rankin Scale scores (0.51 points higher) indicating greater disability 4
  • Lower Barthel Index scores (10.2 points lower) indicating worse functional independence 4
• Sleep-disordered breathing is associated with:
  • Poor neurological recovery 1
  • Decreased quality of life 1
  • Increased mortality 1

Diagnostic Approach for Sleep Disorders in Stroke Patients

• The prevalence of OSA after stroke is sufficiently high (approaching 40%) that polysomnography may be warranted without prescreening in many cases 1
• Facility-based, multichannel polysomnography is the reference standard for diagnosing OSA, though home monitors may be appropriate for selected patients 1
• Signs and symptoms that warrant diagnostic sleep study in stroke patients include:
  • Snoring, witnessed apneas, or respiratory pauses 1
  • Nonrestorative sleep and/or excessive daytime sleepiness 1
  • Obesity 1
  • Unexplained desaturation or hypoxemia during sleep, while awake, or with exertion 1
  • History of poorly controlled hypertension or congestive heart failure 1

Treatment Benefits and Ongoing Research

• Treatment of OSA with continuous positive airway pressure (CPAP) has been shown to improve:
  • Daytime sleepiness 1
  • Blood pressure 1
  • Sleep-related quality of life 1
  • Physical functioning 1
• Several ongoing clinical trials are investigating whether early treatment of OSA after stroke reduces the risk of recurrent stroke, acute coronary syndrome, and all-cause mortality 1

Clinical Approach Algorithm

1. Evaluate for polycythemia etiology:

   • If secondary polycythemia is present, consider OSA as a potential cause 3
   • Recognize that both polycythemia and OSA independently increase stroke risk 3

2. Screen for sleep disorder symptoms:

   • Assess for snoring, witnessed apneas, excessive daytime sleepiness, and morning headaches 1
   • Consider using validated screening tools like the Epworth Sleepiness Scale 1

3. Order polysomnography when:

   • Patient has polycythemia with no other clear cause 3
   • Patient has symptoms suggestive of sleep-disordered breathing 1
   • Patient has had a stroke and shows poor recovery despite appropriate rehabilitation 4

4. Initiate appropriate treatment if OSA is diagnosed:

   • CPAP therapy is the standard treatment 1
   • Treatment may improve both the polycythemia and reduce risk of recurrent stroke 1, 3

Important Caveats

• While OSA is common in stroke patients, the Canadian Stroke Best Practice Recommendations note that the SAVE trial did not show that CPAP treatment significantly reduced the risk of recurrent stroke or major cardiovascular events 1
• The American Society of Hematology suggests against routine screening with formal polysomnography for asymptomatic patients with sickle cell disease, though this may not apply to secondary polycythemia after stroke 1
• Optimal timing of testing and treatment in relation to stroke onset remains under investigation 1