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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.