Sleep Apnea: A Novel Risk Factor in Acute Stroke and Transient Ischemic Attack

Abstract

Obstructive sleep apnea (OSA) is a prevalent disease and has been increasingly recognized as an independent risk factor for hypertension, diabetes, cardiovascular disease, and stroke. Stroke is a frequent disease, a second leading cause of death worldwide which generates high healthcare costs. Recent studies suggest that sleep apnea is common after stroke with the prevalence of 50-94%. OSA is emerging as one of the important risk factors for stroke. Untreated OSA contributes to poor stroke outcome and also is a risk factor for subsequent cardiovascular diseases including recurrent stroke. Treating sleep apnea improves recovery from stroke and decreases cardiovascular morbidity & mortality. Nonetheless, the under-diagnosis of OSA in stroke patients is still common. Considering that typical symptoms of OSA are not often found in stroke, as well as none of the predictors regarding stroke characteristics can identify the presence of sleep apnea in stroke screening in stroke patients. Obstructive sleep apnea (OSA), the most common form of sleep disordered breathing (SDB), is characterized by repetitive episodes of complete (apnea) or partial (hypopnea) airway obstruction during sleep despite respiratory effort resulting in repeated arousals, sleep fragmentation and hypoxia during sleep. Classic symptoms of OSA include snoring, witnessed apnea, choking during sleep, excessive daytime sleepiness or fatigue. OSA is common in the general adult population and may occur in up to 24% of men and 9% of women.1 It becomes more prevalent with increasing age; approximately 70% of older men and 56% of older women.2 Regarding underlying diseases, its prevalence seems to be even higher among patients with neurological diseases such as Parkinson’s disease, Alzheimer’s disease, myotonic dystrophy, epilepsy as well as stroke. OSA is common after stroke, and stroke appears to be more common in those with OSA. Moreover, there are shared risk factors for both. So the question remains, stroke causes sleep apnea, or sleep apnea leads to stroke, or are they both caused by the same risk factors? This is important because it may have implications for prevention, acute treatment, and rehabilitation of patients with acute stroke. There is actually extensive research over the past 2 decades. In this review, the accumulating evidence of sleep apnea and stroke is summarized, regarding prevalence, predictors, causative relationship, and consequences of untreated OSA in stroke patients as well as possible mechanisms responsible for OSA leading to stroke.