Discrepancy Between Subjective and Objective Cognitive Performance in Relation to Depression 6 and 12 Months Post COVID-19

Background/Significance

Few studies of cognitive long-term effects from COVID-19 convalescents include both self-reported subjective cognitive decline (SCD) and objective cognitive function (OCF). Moreover, few studies control for ongoing psychiatric disorders which might confound both level of SCD and performance-based assessments. The present study aims to combine SCD and OCF to explore cognitive functions and potential discrepancy between SCD and OCF 6 and 12 months after COVID-19, to investigate the effect of depression, and compare these results to healthy, confirmed SARS-Cov-2 antibody negative, controls.

Methods

76 patients with confirmed Covid-19 infection reporting neurological symptoms (including cognitive complaints, fatigue, and headache) were recruited from a Norwegian national multicenter study. At 6 (T1) and 12 (T2) months post SARS-CoV-2 infection, they completed a neuropsychological examination covering motor function, processing speed, attention/working memory, verbal fluency, executive function, verbal, and visual memory and a psychiatric evaluation using the M.I.N.I interview. To assess SCD, items expressing cognitive function were extracted from an extended version of the Giessner Beschwerde Bogen (GBB) questionnaire. An objective-subjective discrepancy score was calculated based on standardized scores on self-report and test performance. 67 healthy controls, testing negative for SARS-CoV-2 antibodies, completed GBB and neuropsychological testing.

Results

At T1 post COVID-19 patients had significantly (p < 0.05) lower test performance across all cognitive domains except verbal fluency and motor function, and reported more SCD, compared to healthy controls. At T2 only verbal memory was significantly impaired (p=0.014), and within patients all cognitive domain scores, except verbal fluency, improved significantly from T1 to T2 (p < 0.001 to 0.013) compared to controls. 34.8 percent of patients fulfilled diagnostic criteria for a depressive disorder in the time period after infection until T1, and 21.5 percent between T1 and T2. Depressed compared to non-depressed patients had significantly lower performance in tests measuring attention/working memory at T1, at T2 attention/working memory and executive function. Depressed patients displayed significant differences in discrepancy score (more SDC relative to test performance) across all cognitive domains compared to non-depressed patients at both assessments.

Discussion

In line with previous studies, we report significantly impaired cognitive function in COVID -19 convalescents (1). However, cognitive functions, except verbal memory, improved significantly from 6 to 12 months post COVID-19 to the same level as healthy controls. As expected from other studies depression impaired attention and executive function (2), but also lower the self-evaluation accuracy of cognitive function. Depressed patients reported more subjective cognitive symptoms relative to test performance indicating a subjective underestimation of cognitive function.

Conclusion/Implications

Studies assessing cognitive function in post COVID-19 patients should not only rely on self-reported cognitive symptoms but also include standardized neuropsychological assessment and take into account psychiatric morbidity. Although most cognitive function improve within a year post COVID-19, verbal memory seems to be especially vulnerable to long term impairment and should be addressed in rehabilitation programs.

References

1. Velichkovsky BB et al, Acta Psychol (Amst) 2023 Mar;233:103838.

2. Rock PL et al, Psychol Med 2014 Jul;44(10):2029-40.