Obstructive sleep apnea (OSA) is a severe disorder with a high prevalence. Psychiatric comorbidities, especially depressive symptoms and cognitive dysfunction, are often described in OSA patients. This narrative review aims to examine: (1) the relationship between obstructive sleep apnea syndrome (OSAS) and depressive and cognitive symptoms, and (2) the effect of OSAS treatment on psychiatric symptoms.
Articles that were published between January 1990 and August 2018 were searched and extracted via PubMed, and Web of Science databases. Authors analyzed the papers and its references using the following keywords: obstructive sleep apnea, depression, cognitive dysfunction, anxiety disorders, and continuous positive airway pressure (CPAP). A total of 632 articles were nominated. After the selection according to the inclusion and exclusion criteria, 172 articles were chosen. After complete inspection of the full texts, finally, 58 papers were selected. Secondary papers from the reference lists of the primarily designated papers were also searched, assessed for suitability, and added to the first list of the papers (n = 67). In total, 125 papers were included in this review.
There is a significant overlap in depressive, anxious and OSA symptoms. Studies also show that attention, working memory, episodic memory, and executive functions are decreased in OSA. Conversely, most of verbal functions remain intact and variable results are found in psychomotor speed. Several studies implicated that in some fields of cognitive functions (eg, attention) deficit caused by untreated OSA can be irreversible and shows only partial recovery after a period of treatment with CPAP.
Untreated OSA impacts affective disorders, and often leads to decline of cognitive functions or even leads to permanent brain damage. Further studies are needed to analyze the connection between OSA and affective disorders, anxiety disorders and its effect on cognitive functions more thoroughly, especially in the context of CPAP treatment.

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