The duration of disease prior to therapy in these patients is unknown, but it is notable that patients with frank cognitive deterioration were excluded; whether more severe cognitive impairment would improve with therapy for sleep-disordered breathing remains unknown. It is possible that if left untreated, these changes could progress and become irreversible. Thus, emphasis should be placed on early diagnosis and treatment of OSAS.
Newer stimulant medications like armodafinil have been shown to improve not only sleepiness but also long-term memory (Roth et al. Sleep Breath. 2008;12[1]:53). Although these medications are FDA-approved for the treatment of residual sleepiness in patients with treated sleep apnea, their role in improving cognitive function needs to be evaluated further.
Dr. Chitra Lal, FCCP
It is important for sleep medicine physicians to be cognizant of the effects of OSAS on cognitive function and to screen for it in their clinics. One simple screening instrument is the MCFSI (Mail-In Cognitive Function Screening Instrument), which is a self-administered test designed to identify cognitive impairment (Walsh et al. Alzheimer Dis Assoc Disord. 2006;20(4 Suppl 3):S170). The authors have found this tool to be a quick and effective screening tool in their patients with OSAS, although large studies validating it in this population are lacking.
It is our practice to refer patients with significantly abnormal scores on preliminary tests to a neuropsychologist for complete evaluation, which could involve the administration of tasks specifically designed to test for vigilance and working memory like the psychomotor vigilance task and digit span, providing more objective evidence of cognitive impairment. It also serves as a baseline for the individual patient for long-term follow-up.
The long-term implications of OSAS on cognitive function are just beginning to be realized. The importance of early diagnosis and treatment of OSAS is becoming more evident, as we may be able to stop or partially reverse some of the underlying neurologic abnormalities with treatment. Given the strong association between OSAS and cognitive impairment, we recommend that all patients with MCI or frank dementia be screened for OSAS as a potentially reversible cause of these conditions; polysomnography should subsequently be offered to those patients who are deemed to be high risk for having OSA. Discussions with cognitively impaired patients about the implications of nonadherence with CPAP should be reiterated at each visit, particularly given the significant barrier that such impairment may create to reliable use of therapy.
Drs. Walters and Lal are from the Division of Pulmonary, Critical Care, Allergy and Sleep Medicine, Medical University of South Carolina, Charleston, SC.
Editor’s Note
Evidence continues to mount demonstrating the multiple systemic effects of sleep apnea; in this month’s Sleep Strategies, Drs. Walters and Lal review the cognitive repercussions of untreated sleep-disordered breathing. Given what we know about the growing prevalence of sleep apnea, should we consider more aggressive screening for OSA in patients demonstrating cognitive decline in much the same way we screen those with refractory hypertension or atrial fibrillation? While the sheer volume of referrals that could stem from such a practice may be daunting, the opportunity to potentially impact the natural history of dementia seems too promising to ignore.
Dr. David Schulman, FCCP, Section Editor