AcuteCare Telemedicine Blog

The Importance of Recognizing Sleep Disordered Breathing in Patients with Cognitive Dysfunction

Awareness of sleep disorders has increased over the past several years, leading more physicians to appreciate that Obstructive Sleep Apnea (OSA) is an independent risk factor for hypertension, cardiovascular disease and stroke. Although seemingly overlooked, studies as far back as 15 years have also suggested that OSA may be a risk factor for cognitive dysfunction.

When patients present to a neurologist with complaints of cognitive dysfunction, most are screened for potentially reversible causes such as vitamin B12 deficiency, hypothyroidism, undiagnosed/untreated syphilis, or normal pressure hydrocephalus. If all laboratory and imaging studies are normal, these patients are often started on acetylcholinesterase inhibitors, in hopes of slowing down the rate of cognitive decline.  Screening for sleep apnea, however, is often times not performed. As a result, the opportunity to treat an otherwise harmful disorder and potentially reverse cognitive impairment is forfeited.

In 2010, an article was published in the New York Times entitled “When Sleep Apnea Masquerades as Dementia.” A case study was reported: “The woman was only in her 60s but complained that she was having trouble concentrating.” She couldn’t follow a television program or stay focused during a conversation. As he evaluated the woman, the physician asked, as he usually does, how she was sleeping. The woman, who lived alone, hadn’t noticed any problems. Her son, however, had stayed with her the previous night to drive her to the appointment. “She was snoring like a freight train,” he reported.  Overnight sleep testing determined that the woman had obstructive sleep apnea – nightlong interruptions in breathing that reduce oxygen flow to the brain and prevent deep sleep. The interruptions are quite common in older adults, exacerbating – or sometimes mimicking – dementia symptoms. Treated with a CPAP (continuous positive airway pressure) machine her scores on neuropsychological tests eventually climbed back into normal range.

Another recent study published in JAMA, also showed that sleep disordered breathing may contribute to the development of dementia. 298 women 65 years or older and without dementia were enrolled in this study, undergoing overnight polysomnography testing. Those who were found to have sleep disordered breathing were more likely to have developed cognitive impairment or dementia on follow up testing. It is thought that hypoxemia resulting from sleep disordered breathing is responsible. Dr Michael J. Thorpy, director of the Sleep-Wake Disorders Center at the Montefiore Medical Center in the Bronx, NY stated “We used to think that impaired sleep caused cognitive impairment, but this shows that nocturnal hypoxemia plays an important role and this suggests that the cognitive impairment might be partially reversible in some cases.

Although further studies are needed, these findings do stress the importance of screening patients with complaints of cognitive dysfunction for sleep apnea.  Because the large majority of people who develop dementia do so after the age of 65, it would seem imperative to screen younger patients with cognitive complaints for sleep disordered breathing.

Obstructive Sleep Apnea and Atherosclerosis

Atherosclerosis is the leading cause of stroke and cardiovascular disease, the leading causes of death internationally, but recently, obstructive sleep apnea (OSA) has also been found to be an independent risk factor for stroke. One explanation may lie in the propensity towards the development of atherosclerosis in this disorder. Identifying this and other potential risk factors of atherosclerosis and understanding how these risk factors behave independently and comorbidly will hopefully reduce the risk of atherosclerotic disease, ultimately aiding in the prevention of stroke.

OSA is a lesser known independent risk factor for stroke than hypertension (HTN), but both are frequently observed as comorbidities in patients with cardiovascular disease and stroke. In 2009, a study published in Hypertension found that patients with OSA and patients with HTN had an increase in carotid wall thickness compared to controls by 19.4% and 19.5% respectively. In patients with OSA and HTN, the increase was found to be 40.3% in carotid wall thickness over controls. These and other findings strongly suggest that OSA is indeed an independent risk factor for the development of carotid atherosclerosis.

OSA has been shown to independently increase several markers of atherosclerosis including sympathetic activity, pro inflammatory factors and endothelial dysfunction. In addition, OSA can lead to other atherosclerotic risk factors such as alteration in lipid metabolism, insulin resistance and hypertension.  In 2007, a separate study published in the American Journal of Respiratory and Critical Care Medicine involved twenty-four patients with OSA and without comorbidities. After 4 months of treatment with continuous positive airway pressure, there was a reduction in markers of inflammation and sympathetic activation as well as a decrease of carotid wall thickness; again evidence to suggest OSA as a risk factor for atherosclerosis.

The importance of these studies and others suggesting OSA as an independent risk factor for atherosclerosis is to arm physicians with more ways to combat the incidence of stroke and cardiovascular disease. Because of the high incidence of OSA in patients with HTN, control of HTN alone may not adequately reduce atherosclerotic risk. Screening tools such as the STOP/BANG and Berlin questionnaire should be utilized in  hypertensive patients, particularly those with refractory disease (>3 BP meds with adequate control or 3 BP meds with inadequate control). Overnight polysomnography should be performed in patients identified at risk for OSA and treatment should be initiated when appropriate. Likewise, in patients without known atherosclerotic risk factors but suspected OSA, screening and diagnostic studies should be performed. These measures can help to further reduce the incidence of atherosclerosis and subsequently reduce the incidence of cardiovascular disease and stroke.

Before Stroke Strikes

The fight against stroke, the second leading cause of death worldwide and leading cause of disability, begins long before a patient’s arrival to the ER. Awareness by physicians of common modifiable risk factors, including hypertension, diabetes and hyperlipidemia is key to the decrease the incidence of stroke. Obstructive sleep apnea (OSA), one such relatively common modifiable risk factor, is often unrecognized and underdiagnosed.

OSA is a disorder characterized by repetitive airway collapse, leading to arousals and oxygen distortions. It is well known that when these events occur, there is an increase in sympathetic tone and a rise in systemic blood pressure. OSA has also been found to be associated with an increase in proinflammatory and prothrombotic factors, both of which can lead to atherosclerosis and subsequent cardiovascular disease and stroke.

The results of the Sleep Heart Health Study, a 9 year prospective cohort study designed to determine risks associated with OSA, showed that OSA is an independent risk factor of stroke. It is estimated that over 15 million Americans have OSA, the majority of whom go undiagnosed.

Identifying patients at risk (i.e. those with obesity, loud snoring, excessive daytime sleepiness, etc.) should prompt consultation with a sleep disorders specialist. Appropriate work up and management should be implemented with an emphasis on treatment compliance. Public and professional awareness of the potential dangers of untreated OSA is crucial to a further decrease in stroke related morbidity and mortality.