Neural base of persistent hyposmia after COVID-19

An Italian group provided the first evidence of cortical hypometabolism in patients with isolated persistent hyposmia after COVID-19 without severe respiratory distress. They conclude that ¹⁸F-FDG-PET may play a role in the identification of long-term brain functional sequelae of COVID-19.

Hyposmia is often not only the first symptom of COVID-19, but its persistence is also a relatively frequent neurological complication of the infection. Little is known about the neural bases of hyposmia persisting after the patient's recovery from COVID-19. Dr Matteo Pardini (University of Genoa, Italy) and colleagues evaluated the presence of regional brain hypometabolism in patients with persistent isolated olfactory dysfunction after recovery from COVID-19. A total of 22 patients underwent whole-body ¹⁸F-FDG-PET at least 4 weeks after their recovery, 14 of whom had isolated persistent hyposmia. A voxelwise analysis was used to identify brain regions of relative hypometabolism in patients with hyposmia, compared with 61 healthy controls.

Patients with hyposmia after COVID-19 were characterised by relative hypometabolism in parahippocampal and fusiform gyri in both hemispheres and in left insula compared with controls. Structural connectivity maps showed that the hyposmia cluster was included in the bilateral longitudinal fasciculi, with a probability score of 0.82 and 1.0 for the right and left inferior longitudinal fasciculus, respectively.

“One of the hypotheses to explain hyposmia in COVID-19 patients –in the absence of nasal congestion– is that the virus enters the CNS through the first neurons of the olfactory pathway located in the olfactory mucosa,” Dr Pardini explained. “The present evidence of hypometabolism in two symmetrical, similar regions within the limbic cortex may support the occurrence of a distal involvement of the olfactory pathway. Moreover, the involvement of the inferior longitudinal fasciculus is in line with observations of its role in hyposmia in Parkinson's disease, HIV, and hepatitis C.”

1. Pardini M, et al. Brain metabolism and persistent olfactory deficits after SARS-CoV-2 infection: an FDG-PET study. OPR-142, EAN 2021 Virtual Congress, 19–22 June 2021.

 

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Posted on 18 August 202118 August 2021