Obstructive sleep apnea, hypothyroidism and cognition

Objectives: To assess the impact of obstructive sleep apnea syndrome (OSAS), obesity and hypothyroidism and their potential synergic effect on sleep pattern, vigilance and cognitive functioning. Methods: Fifty OSAS patients and twenty age, sex and BMI matched healthy controls underwent in lab nocturnal polysomnography, multi- ple latency sleep test, standardized questionnaires for sleep quality, fatigue, sleepiness, TSH, fT3 and fT4 evaluation and neuropsycho- logical tests. Subjects were divided in four groups: non obese OSAS, obese OSAS, hypothyroid OSAS patients and healthy controls. Results: Hypothyroid OSAS showed worse scores in subjective sleep quality and fatigue compared with controls and non obese OSAS, with a positive correlation between TSH level and Fatigue Severity Scale and Epworth Sleepiness Scale. Mean daily sleep latency was significantly lower in all three clinical population as compared to control, while single naps latencies were different mainly for hypothyroid OSAS. Neuropsychological testing pointed out no significant differences among the three OSAS groups, but OSAS patients, considered as a whole, showed decreased performances in attentive and executive frontal tasks, compared with healthy controls. Sleep efficiency and Wake After Sleep Onset and microstructural sleep variables showed significant correlations with attentive and executive frontal tasks. Conclusions: Sleepiness and perceived fatigue occur particularly in hypothyroid OSAS patients. Cognitive deficit was similar among the three OSAS groups and impaired compared with healthy controls. The observed correlation between neuropsychological examination and macro and microstructural variables suggest a role of sleep disruption, more than respiratory disturbance per se, on cognition.