Sleep Apnea in Patients With Transient Ischemic Attack and Minor Stroke
Opportunity for Risk Reduction of Recurrent Stroke?
Background and Purpose—Patients with TIA and minor stroke are at high risk for recurrent stroke. Obstructive sleep apnea (OSA) may increase this risk. The objectives of our study were to determine the prevalence and severity of OSA and its clinical presentation in this population.
Methods—Patients who presented with TIA and minor stroke completed a questionnaire and nocturnal cardiopulmonary monitoring to diagnose OSA and associated nocturnal hypoxia.
Results—Sixty-six patients completed the study; 62% had OSA (respiratory disturbance index >5). Forty-four percent of these patients had moderate or severe OSA (respiratory disturbance index >15) that was associated with significant nocturnal hypoxia. Most patients did not have the typical clinical features of OSA, such as obesity and daytime sleepiness.
Conclusions—Patients who experience TIA and minor stroke have a high prevalence of OSA and associated hypoxia. The atypical clinical presentation of OSA in this patient population may lead to under-recognition and treatment. Further studies are required to determine the impact of treating OSA on the risk of recurrent stroke.
Because patients who experience TIA or minor stroke have an increased risk of recurrent stroke,1 the identification of novel factors, such as obstructive sleep apnea (OSA), that may increase this risk is critical for the development of new therapies. The objectives of this study were to determine the prevalence and severity of OSA in this population to describe their clinical profile and to compare their neurological outcomes 3 months later.
Subjects and Methods
Patients admitted for management of acute TIA or minor stroke (NIHSS score <6) were screened. All patients received conventional management for their TIA or minor stroke and gave informed consent that was approved by the institutional Ethics Board.
The neurological deficit was assessed using the NIHSS score. The modified Rankin scale was used to assess patients’ functional capacity.
All patients completed a questionnaire regarding their medical history and sleepiness (Epworth Sleepiness Scale score >10).2
Nocturnal Cardiopulmonary Monitoring for Sleep Apnea
Overnight cardiopulmonary monitoring (Remmers Sleep Recorder, Saga Tech) was performed at home or in hospital. This device continuously measures oxyhemoglobin saturation, heart rate variability, airflow, snoring, and body position. The respiratory disturbance index (RDI) was calculated based on the number of episodes of oxyhemoglobin desaturation greater than 4% divided by the duration of the recording. Sleep apnea severity was defined as mild (5≤RDI<15), moderate (15≤RDI<30), and severe (RDI≥30).3 Apnea was classified as central (Cheyne-Stokes respiration [CSR]) or obstructive (OSA), based on the morphology of the airflow recordings. The severity of nocturnal hypoxia was quantified by the duration of oxyhemoglobin saturation <90% during the recording.
Patients were reassessed by a stroke neurologist 3 months later, who repeated the NIHSS and modified Rankin Scale, and classified the patients’ stroke as hemorrhagic or ischemic based on brain imaging. The etiology of ischemic strokes was further classified using the TOAST classification.4 Patients with an RDI >5 were also reassessed at the sleep clinic 3 months after their stroke, which included nocturnal cardiopulmonary monitoring.
Data are reported as mean±SD. Unpaired t test was used to compare continuous variables between 2 groups, and 1-way analysis of variance with a Tukey post hoc (α=0.05) was used for comparison between 3 groups. Categorical comparisons were analyzed using the χ2 test, and contingency analysis of 2×2 tables was performed via Fischer exact test.
Two hundred thirteen patients met the inclusion criteria; 140 were invited to participate, of whom 84 consented. Eighteen patients withdrew because of problems with cardiopulmonary monitoring. Sixty-six patients completed the study, all of whom had an ischemic stroke or TIA.
Prevalence of Sleep Apnea
Forty-seven patients (71%) had sleep apnea (RDI >5), of whom 41 (87%) had OSA and the remaining 6 (13%) had Cheyne-Stokes respiration (Figure). Among the 41 OSA patients, the proportion who had mild, moderate, and severe sleep apnea was 56%, 24%, and 20%, respectively. The prevalence of OSA was higher in those whose baseline NIHSS was >0 (68%) vs those whose NIHSS was 0 (32%; P<0.001). Patients with OSA had more severe nocturnal hypoxia than those without apnea, especially those with moderate and severe OSA (Tables 1 and 2⇓).
Patients with OSA were more commonly male, were heavier, had a larger neck circumference, and had a higher frequency of hypertension than those without apnea (Table 3). The majority of OSA patients did not report significant daytime sleepiness (Epworth Sleepiness Scale score >10). Although OSA patients reported a higher frequency of witnessed apneas, there was no difference between groups in the frequency of snoring, nocturnal choking, or unrefreshing sleep.
Relationship Between Sleep Apnea and TIA or Minor Stroke
The mean RDI did not change significantly in patients with OSA 3 months after their minor stroke (19.4±15.7 to 18.7.1±16.9; n=30). There was no significant difference in the change in NIHSS and modified Rankin Scale scores between baseline and the 3-month follow-up. With regard to stroke etiology, there appeared to be a higher prevalence of small vessel disease in patients with OSA compared to those without apnea (20% vs 11%; P<0.0001).
We found a high prevalence of sleep apnea (71%), which was predominantly OSA (85%), in patients with TIA and minor stroke. Most patients with OSA did not have the typical clinical features, such as obesity and daytime sleepiness.
OSA was still present 3 months later when their neurological deficit had mostly resolved. This supports the notion that OSA predated the onset of their TIA or minor stroke and that OSA contributed to its pathogenesis. Because the cardiovascular complications of OSA are thought to be mediated through the biological effects of nocturnal hypoxia,5 we quantified how much hypoxia patients with OSA were exposed to and found that it was significant, particularly in those with moderate and severe disease. Further studies are required to determine if the diagnosis and treatment of OSA in this population provide an opportunity to reduce the risk of recurrent stroke.
- Received July 12, 2010.
- Accepted August 19, 2010.