Structural brain changes in post‐acute COVID‐19 patients with persistent olfactory dysfunction

Abstract Objective This research aims to study structural brain changes in patients with persistent olfactory dysfunctions after coronavirus disease 2019 (COVID‐19). Methods COVID‐19 patients were evaluated using T1‐weighted and diffusion tensor imaging (DTI) on a 3T MRI scanner, 9.94 ± 3.83 months after COVID‐19 diagnosis. Gray matter (GM) voxel‐based morphometry was performed using FSL‐VBM. Voxelwise statistical analysis of the fractional anisotropy, mean diffusivity (MD), radial diffusivity (RD), and axial diffusivity was carried out with the tract‐based spatial statistics in the olfactory system. The smell identification test (UPSIT) was used to classify patients as normal olfaction or olfactory dysfunction groups. Intergroup comparisons between GM and DTI measures were computed, as well as correlations with the UPSIT scores. Results Forty‐eight COVID‐19 patients were included in the study. Twenty‐three were classified as olfactory dysfunction, and 25 as normal olfaction. The olfactory dysfunction group had lower GM volume in a cluster involving the left amygdala, insular cortex, parahippocampal gyrus, frontal superior and inferior orbital gyri, gyrus rectus, olfactory cortex, caudate, and putamen. This group also showed higher MD values in the genu of the corpus callosum, the orbitofrontal area, the anterior thalamic radiation, and the forceps minor; and higher RD values in the anterior corona radiata, the genu of the corpus callosum, and uncinate fasciculus compared with the normal olfaction group. The UPSIT scores for the whole sample were negatively associated with both MD and RD values (p‐value ≤0.05 FWE‐corrected). Interpretation There is decreased GM volume and increased MD in olfactory‐related regions explaining prolonged olfactory deficits in post‐acute COVID‐19 patients.