WASHINGTON, DC—Patients with stroke and sleep apnea may have worse memory and executive function, compared with individuals with sleep apnea alone, those with stroke alone, and those with neither diagnosis, according to research presented at the 67th Annual Meeting of the American Academy of Neurology. The combination of stroke and sleep apnea may not be associated with greater global cognitive impairment, however, compared with stroke and sleep apnea individually.

Stroke and sleep apnea have been associated with cognitive difficulties. Jennifer Molano, MD, Assistant Professor of Neurology at the University of Cincinnati Neuroscience Institute, and colleagues examined the association between sleep apnea, stroke, and cognitive performance by analyzing data from the Reasons for Geographic and Regional Differences in Stroke (REGARDS) study.

The REGARDS study enrolled approximately 30,000 blacks and whites age 45 and older in the United States between 2003 and 2007 with the aim of investigating factors associated with increased stroke mortality in blacks and in the southeast. Baseline assessment included a telephone interview and a home visit. Participants were followed up every six months. The investigators added a brief cognitive battery in May 2008, and a module with questions about sleep was included in follow-up assessments in September 2008.

A Retrospective Review of REGARDS Data
In their study, Dr. Molano and colleagues included participants who had a cognitive assessment within two years after completing a sleep module. Sleep apnea was defined by self-report. Stroke was identified by a self-report of stroke at baseline or an incident stroke determined after a review of medical records before the individual’s completion of the sleep module.

Global cognitive impairment was assessed by the Six-Item Screener and dichotomized as positive if the score was four or lower. Verbal memory was assessed through the Word List Learning (WLL) and the Word List Delayed Recall (WLD) scores. Executive function was assessed through Animal Fluency (AF) and Letter Fluency (LF) scores. Higher scores on the tests for verbal memory and executive function indicated better cognition.

Dr. Molano’s team conducted multiple regression analyses and adjusted the results for demographics, which included race, gender, region, education, and income. The researchers adjusted the data further for comorbidities and covariates, including hypertension, diabetes, dyslipidemia, BMI, and daytime sleepiness.

Stroke and Sleep Apnea Decreased Verbal Memory
Approximately 22,000 participants had a cognitive assessment and completed the sleep apnea module. About 83% of participants had neither sleep apnea nor stroke, 10% had sleep apnea only, 5% had stroke only, and 1% had stroke and sleep apnea. Patients with stroke alone were more likely to be older and black, and more likely to have low income and low education. Participants with stroke and sleep apnea had more comorbidities.

The unadjusted results indicated that mean verbal memory and executive function performance were highest for patients without stroke or sleep apnea and lowest for patients with stroke and sleep apnea. Mean WLL scores were 16.3 for controls, 15.8 for the sleep-apnea group, 14.5 for the stroke group, and 13.3 for the stroke-and-sleep-apnea group. Mean WLD scores were 6.2 for controls, 5.9 for the sleep-apnea group, 5.4, for the stroke group, and 5.0 for the stroke-and-sleep-apnea group. Mean AF scores were 15.4 for controls, 15.1 for the sleep-apnea group, 13.6 for the stroke group, and 13.2 for the stroke-and-sleep-apnea group. Mean LF scores were 10.0 for controls, 9.7 for the sleep-apnea group, 8.8 for the stroke group, and 8.0 for the stroke-and-sleep-apnea group.

After data were adjusted for demographics, the group with stroke and sleep apnea had the lowest scores for verbal memory and executive function, followed by the stroke group, the sleep-apnea group, and those with neither disorder. The results were slightly attenuated but still statistically significant after data were adjusted for comorbidities. In the adjusted and unadjusted models, the stroke-only group had the highest proportion of global cognitive impairment.

Dr. Molano acknowledged several limitations of the research. The study was retrospective and did not rely on sleep studies to diagnose sleep apnea. As a result, the severity of sleep apnea and degree of hypoxemia among participants was uncertain. The study also did not identify the type of stroke or record the size of participants’ strokes.

Future investigations of “people who have a history of stroke that include polysomnographic data, neuroimaging, and full neuropsychologic testing may be needed to further clarify exactly what this association between sleep apnea, stroke, and subsequent cognitive performance means,” said Dr. Molano. “Sleep apnea does have a treatment. If we can treat people with sleep apnea … does that have implications for recovery after stroke?”

—Erik Greb

How Do Stroke and Sleep Apnea Affect Cognition?