Persistent olfactory dysfunction after COVID-19 is associated with reduced perfusion in the frontal lobe

Abstract

Background: Olfactory dysfunction is common during SARS-CoV-2 infection. The pathophysiology of the persistence of this symptom and the potential relationship with central nervous system involvement is unknown.

Aim of the study: To evaluate the neural correlates of persistent olfactory dysfunction in a series of patients with post-COVID syndrome.

Methods: Eighty-two patients with post-COVID syndrome were assessed with the Brief Smell Identification Test and a multimodal MRI study including 3D-T1, T2-FLAIR, diffusion-tensor imaging, and arterial spin labeling. Olfactory and neuroimaging examinations were performed 11.18 ± 3.78 months after the acute infection. Voxel-based brain mapping analyses were conducted to correlate the olfactory test with brain volumes, white matter microstructure, and brain perfusion.

Results: Olfactory dysfunction was associated with lower tissue perfusion in the orbital and medial frontal regions in the arterial spin labeling sequence. Conversely, no statistically significant findings were detected in brain volumes and diffusion-tensor imaging. Mild changes in paranasal sinuses and nasal cavities were detected in 9.75% of cases, with no association with olfactory deficits.

Conclusions: We provide new insights regarding the pathophysiology of persistent olfactory dysfunction after COVID-19, involving the main brain regions associated with the olfactory system.

Keywords: COVID-19; MRI; anosmia; neuroimaging; olfactory; post-COVID syndrome.