Comorbid Alzheimer's disease and OSAS: does CPAP slow cognitive decline?

The results of the study, “Sustained use of CPAP slows deterioration of cognition, sleep, and mood in patients with Alzheimer's disease and obstructive sleep apnea: a preliminary study,1” reported in this issue of the Journal of Clinical Sleep Medicine, suggest that treatment of obstructive sleep apnea syndrome (OSAS) with continuous positive airway pressure (CPAP) may delay cognitive decline in older adults with Alzheimer's disease and related dementias (AD). In this study, the investigators contacted all participants who had completed a 6-week randomized controlled trial (RCT) of the use of CPAP in persons with mild to moderate dementia and OSAS after approximately 1 year had elapsed. Of those people called, 5 reported still using their CPAP (CPAP+). They were matched by time of completion of the initial study with 5 participants who reported discontinuing CPAP use (CPAP−). A home overnight polysomnogram on CPAP was conducted in the CPAP+ group, and both groups repeated the neuropsychological test battery and sleep and mood questionnaires used as outcome measures in the RCT. The authors reported that sustained CPAP use in patients with AD resulted in moderate to large effect sizes on cognitive measures, depressive symptoms, daytime sleepiness, and patient and caregiver subjective sleep quality. Congratulations to the authors for addressing a highly significant health care problem with few viable solutions. Dementia is becoming a highly relevant personal and public health concern.2 In 2000, the prevalence of AD in the United States was estimated at 4.5 million, and this figure is projected to increase to 14 million by 2050.2 OSAS is common in patients with AD, with a greater than 40% prevalence in those who are institutionalized.3 Unfortunately, few behavior or pharmacologic interventions effectively delay cognitive decline and preserve nighttime sleep duration and quality in older adults with AD, and institutionalization is often the result because caregivers are burdened and exhausted from the demands of around-the-clock care. Despite enthusiasm for the significance of the problem addressed in this preliminary study and the importance of the findings, there are several methodologic limitations, and the authors highlight most of them. CPAP+ was based on self-reported CPAP use. Downloading the mean number of hours of CPAP use from the CPAP device would have provided additional evidence of CPAP use in the CPAP+ group. Further, the small sample size of only 5 participants in the CPAP− and CPAP+ groups and the absence of an RCT design limit the conclusions that can be drawn from this study about the efficacy of long-term CPAP treatment for patients with AD. Selection bias and nonequivalence of the CPAP− and CPAP+ groups are additional concerns. For example, it is possible that the CPAP− group did not use their CPAP because their cognitive status was worsening. Also, the CPAP− group may have had a “global nonadherence” pattern, and they may not have adhered to other medical therapies, such as the use of cognition-enhancing medications. Another concern is that, based on the cognitive measures, it appears that the groups were probably different at the end of the RCT, with the CPAP− group being somewhat more impaired, particularly in executive performance on the Trails B test. Despite these limitations, the preliminary findings in this study strongly support the need for an RCT investigating the long-term effects of treatment of comorbid OSAS and AD with CPAP. Stabilizing cognition in older adults with AD could help maintain their independence, delay admission to long-term care facilities, reduce burden for their caregivers, and reduce healthcare costs for society.