OBJECTIVE: Assessment of olfactory function with psychophysical testing requires cognitive demand to correctly pair test odors with remembered scents. Individuals suffering from long-Corona Virus Disease 2019 (long-COVID-19) may develop a decline in neurocognitive performance, which may be concurrent with persistent olfactory dysfunction (OD). Given the rigorous cognitive demand of the unprompted identification (UI) olfactory assessment, the goal of this study is to understand whether it could serve as a proxy for specific neurocognitive domains during clinical assessment of olfaction.
METHODS: Participants from our long-COVID cohorts with persistent OD underwent a panel of neurocognitive screening followed by olfactory assessment of threshold followed by unprompted (UI) and prompted identification (PI) tests using Sniffin' Sticks. Hierarchical linear mixed-effect models were used to understand the relative impact of each neurocognitive variable after controlling for demographics and olfactory threshold scores.
RESULTS: Neurocognitive variables demonstrated common correlation trends. Models containing Montreal Cognitive Assessment (MoCA) and digit-span backward scores had statistically significant fits for both UI (MoCA: = 10.20, = 0.001/digit-span backward: = 4.27, = 0.04) and PI (MoCA: = 4.51, = 0.03/digit-span backward: = 5.04, = 0.02) linear mixed-effect models, but UI was further explained by logical memory ( = 7.84, = 0.005), verbal fluency ( = 8.79, = 0.003), and digit-span forward ( = 12.30, = 0.0004). These relationships were statistically significant after controlling for demographic and olfactory threshold covariates. χ p χ p χ p χ p χ p χ p χ p2 2 2 2 2 2 2
CONCLUSIONS: UI and PI have interrelated neurocognitive dependence on global cognition (MoCA) and executive function (digit-span backward) among long-COVID participants. As UI draws upon neurocognitive domains of episodic (logical memory), semantic (verbal fluency), and working memory (digit-span forward), the inclusion of a UI task may provide supplementary screening for cognitive impairments in those undergoing clinical olfactory assessment, particularly among those with lingering effects of COVID-19.
