Study shows structural brain changes in post-acute COVID-19 patients with persistent olfactory dysfunction

This could be important when we use general anesthesia on post-acute COVID-19 patients.

Findings from a study published in Annals of Clinical and Translational Neurology showed decreased gray matter (GM) volume and increased mean diffusivity (MD) in olfactory-related regions explaining prolonged olfactory deficits in post-acute coronavirus disease 2019 (COVID-19) patients.deficit is a frequent clinical manifestation of COVID-19; some of these patients present persistent smell loss that lasts even beyond months after symptoms onset. As far as we know, this is the first work to investigate whether COVID-19 patients with prolonged olfactory dysfunction have structural brain changes compared to those with normal olfaction,” wrote Anna Campabadal, University of Barcelona, Barcelona, Spain, and colleagues.

The study included 48 patients with COVID-19 who were infected between February 2020 and May 2021. Patients were evaluated using T1-weighted and diffusion tensor imaging on a 3T magnetic resonance imaging (MRI) scanner at a mean of 9.94 months after COVID-19 diagnosis. The smell identification test (UPSIT) was used to classify patients as normal olfaction (n = 25) or olfactory dysfunction (n = 23) groups. There were no differences in the interval between COVID-19 diagnosis and MRI acquisition and the percentages of admission in the intensive care unit. The group of patients with olfactory dysfunction had significantly more hospitalisation cases than the normal olfaction group.

The researchers observed that COVID-19 patients with olfactory dysfunction had lower GM volume compared with those with normal olfaction in a cluster involving the left amygdala, insular cortex, parahippocampal gyrus, frontal superior and inferior orbital gyri, gyrus rectus, olfactory cortex, caudate, and putamen (378 voxels; Montreal Neurosciences Institute coordinates of cluster maximum: x = −22, y = 10, z = −28; t stat = 4.669;  P = 0.0082).

Additionally, patients with olfactory dysfunction showed higher MD values (t stat = 4.711; P = 0.031) in the genu of the corpus callosum, orbitofrontal areas, the anterior thalamic radiation, and the forceps minor compared to those with normal olfaction, as well as higher RD values (t stat = 4.759; P = 0.043) in the anterior corona radiata, genu of the corpus callosum, and uncinate fasciculus.

There were no significant correlations between GM volume of the olfactory system and the UPSIT. However, UPSIT was negatively associated with both MD (t stat = 0.607; P = 0.040), and RD (t stat = 0.781; P = 0.011) values.

“Although mechanisms leading the neuronal injury are unknown, our data suggest the presence of brain damage, evidenced by increased MD and GM loss in regions of the olfactory system in COVID-19 patients with long olfactory dysfunction pointing out the central nervous system involvement in the persistent COVID symptoms,” the researchers concluded.