Subjective and objective cognitive impairment in patients with obstructive sleep apnea

Abstract Background Obstructive sleep apnea (OSA) is associated with cognitive impairment (CI). We aimed to study subjective cognitive complaint (SCC) and objective cognitive scores, and its relation to polysomnography (PSG) parameters, in patients suspected of OSA. Method Patients suspected of OSA who were scheduled for PSG were recruited. Cognition was assessed by the Montreal Cognitive Assessment (MoCA) and the Color Trails Test (CTT). The Memory index score (MIS) was also calculated from the MoCA. The presence of SCC was assessed by asking patients directly and using the Cognitive Change Index rated by self (CCI‐S) or informants (CCI‐I). Patients with severe dementia were excluded. Result Among 258 patients with an age of 61.46±7.05 years, 51.2% are female. The mean MoCA was 23.89±3.89. Based on PSG, patients were classified as having no OSA to mild OSA (20.1%), moderate (28.3%), and severe OSA (51.6%). Based on cognitive tests, patients with moderate to severe OSA had a higher proportion of objective cognitive impairment (64.1%) but less SCC (38.3%) than patients with no OSA or mild OSA. CCI‐S and CCI‐I scores were significantly correlated with each other (r = 0.238, p = 0.019) but not with MoCA score nor CTT‐time. Objective cognitive tests scores were associated with the number of comorbidities and several PSG parameters, i.e., total sleep time, sleep onset latency, wake after sleep onset, sleep stages, mean O2 saturation, and time spent of SaO2 under 90% (all p<0.05). Meanwhile, subjective cognitive scores were not associated with any PSG parameters. However, the self‐report (CCI‐S) was significantly correlated with the Thai‐Geriatric Depression Scale and the Epworth Sleepiness Scale (r = 0.388 and 0.262, respectively, p <0.001). Thirty patients with severe OSA and CI were followed‐up after CPAP treatment for the mean of 12.2 months and showed a significant improvement on MoCA and MIS scores, but not the CTT and CCI scores. Conclusion Most patients with OSA had objective cognitive impairment, but SCC was found less in a more severe stage of OSA. Several PSG parameters were associated with cognitive scores but not subjective cognitive scores. Patients with severe OSA could have a cognitive benefit after CPAP treatment.