Cognitive impairment ‘highly prevalent’ in patients referred to sleep clinic for OSA

In a new study, the prevalence of mild cognitive impairment was high among patients referred to sleep clinics for suspected obstructive sleep apnea, particularly in older men who had moderate or severe OSA and other vascular comorbidities.

The study focused on mild cognitive impairment in patients with suspected OSA in the sleep clinic, as the researchers noted risk in this population is poorly characterized.

“The underlying mechanisms leading to cognitive impairment in OSA remain poorly understood,” Andrew E. Beaudin, PhD, from the department of clinical neurosciences at Cumming School of Medicine at the University of Calgary, Alberta, Canada, and colleagues wrote in the Annals of the American Thoracic Society. “Potential sleep-related mechanisms of cognitive impairment in OSA patients include nocturnal hypoxemia, sleep fragmentation and excessive daytime sleepiness.”

Researchers recruited 1,084 adults referred to three academic sleep centers for suspected OSA who had home sleep apnea testing or in-laboratory polysomnography. All patients completed sleep and medical history questionnaires and cognitive, verbal learning and symbol coding tests.

A Montreal Cognitive Assessment Test score of less than 26 was defined as mild cognitive impairment. Nearly 48% of patients had mild cognitive impairment, with an increase to more than 55.3% in patients with moderate and severe OSA.

“Cognitive impairment is highly prevalent in patients referred to sleep clinics for suspected OSA,” Beaudin and colleagues wrote.

Patients with mild cognitive impairment were generally older men with severe OSA, hypoxemia and vascular comorbidities.

Researchers reported greater than 70% higher odds for mild cognitive impairment in patients with moderate and severe OSA compared with patients with no OSA (P = .003).

Compared with age-matched normal values, memory and information processing speed among patients with moderate and severe OSA was lower (P < .001), with lower scores in both the Montreal Cognitive Assessment Test (24.8 for both) and Digit-Symbol Coding subtest (–0.6 for moderate OSA; –0.7 for severe OSA) associated with a higher oxygen saturation index and nocturnal hypoxemia, according to the results.

“Individuals with [mild cognitive impairment] are at greater risk of progressing to dementia; and once dementia is clinically apparent, its impact on patients and their caregivers and the economic burden upon the health care system increases substantially,” the researchers wrote. “Thus, it is important to identify patients with [mild cognitive impairment] early in the course of the disease to initiate treatment and mitigate further decline.”

Older patients with severe OSA, nocturnal hypoxemia and vascular comorbidities who are at the highest risk for mild cognitive impairment may need to receive more definitive OSA treatment with more attention and support for CPAP adherence, according to the researchers.

“Further studies are required to determine if such a strategy is feasible, and effective, in reducing the number of OSA patients who progress from [mild cognitive impairment] to dementia,” the researchers concluded.