Cognitive assessment of patients with post-COVID olfactory dysfunction and impaired domains.

Abstract

Background: Persistent olfactory dysfunction is a common symptom of post-COVID syndrome (PCS), particularly among younger patients who experienced mild COVID-19. Recent functional neuroimaging studies suggest that persistent olfactory impairment may be associated with cognitive deficits. However, few studies have characterised cognition in this subgroup using standardised neuropsychological assessment.

Objectives: To assess the prevalence of cognitive deficits and their characteristics in patients with persistent post-COVID olfactory symptoms.

Methods: This multicentre study included 55 patients with PCS and persistent olfactory dysfunction following COVID-19 onset before February 2021. Participants underwent olfactory evaluation using the Sniffin' Sticks test and a comprehensive battery of neuropsychological assessments.

Results: The mean age was 43.9 years (SD 10.1), with a mean disease duration of 46.1 months (SD 6.5). According to a domain-based criterion, 67.3% of patients showed cognitive impairment. Domain-specific impairment was observed in attention/working memory (67.3%), executive function (50.9%), and episodic memory (56.4%). The Montreal Cognitive Assessment (MoCA) detected abnormalities in only 9.1% of patients. Exploratory comparisons between hyposmic and anosmic patients showed no univariate differences after false discovery rate (FDR) correction, despite a marginal post-hoc multivariate effect. Continuous olfactory performance showed inverse correlations with two executive measures after FDR correction, but no consistent dose-response relationship across cognitive measures.

Conclusion: In this selected cohort, a high prevalence of multidomain cognitive alterations was observed. These findings highlight the limitations of brief cognitive screening tools and suggest a complex relationship between persistent olfactory dysfunction and cognition. Further longitudinal studies are warranted.