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

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.

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

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.

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.

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.