Circadian Variations in Cognitive Performance Among Patients With Narcolepsy and Obstructive Sleep Apnea: A Comparative Study.

Background: Patients with narcolepsy experience excessive daytime sleepiness (EDS) and cognitive impairment. However, studies on the circadian variability associated with cognitive impairment in narcolepsy patients are scarce. This study aimed to explore circadian cognitive performance in narcolepsy patients compared with patients with obstructive sleep apnea (OSA) and EDS (OSA-with-EDS). Methods: A total of 62 participants, 29 with narcolepsy and 33 with OSA-with-EDS completed the study. The assessments were done using questionnaires, polysomnography (PSG), the multiple sleep latency test (MSLT), and cognitive-behavioral tasks at different time points (20:00, 08:00, 10:00, 12:00, 14:00, 16:00, and 18:00) including the psychomotor vigilance task (PVT), the Stroop color-word task, and the 2-back task to separately assess the circadian variations of vigilant attention, inhibitory control, and working memory respectively. Results: Narcolepsy patients showed significant within-subject circadian variations in vigilant attention (p < 0.001), inhibitory control (p = 0.016), and working memory (p < 0.001) in the time domain. Overall, vigilant attention in narcolepsy patients presented a pattern with optimal performance observed at 20:00 on the previous night followed by deterioration in the morning (08:00~14:00) and improvement in the afternoon (14:00~18:00). Inhibitory control displayed a pattern of "enhancement in the morning (08:00~12:00) followed by a decline in the afternoon (12:00~18:00)", while working memory displayed a trend of improvement during daytime hours, with these two measures showing their poorest performance at 20:00 on the previous night. Conclusions: Circadian variations were prominently observed in vigilant attention, inhibitory control, and working memory performance among patients with narcolepsy. Except for EDS, the intrinsic disease specificity may play an important role in the cognitive impairments associated with narcolepsy.