Mild COVID has now been shown to be associated with shrinkage of specific brain regions

In an important new study published yesterday in Nature and described in a more accessible form today in the New York Times, researchers studied MRI scans of 785 participants in the UK Biobank.  All of these volunteers had previously had brain MRIs done prior to the COVID pandemic, and they were all reimaged on average three years later. Of the 785 participants, 401 had tested positive for COVID between their two scans and 15 of these were hospitalized due to COVID, leaving 384 unaffected by COVID to serve as controls. The people who had had COVID infections between their two scans showed greater shrinkage in several brain regions involved with olfactory processing and memory including the orbitofrontal cortex, parahippocampal gyrus, insula, and others. This difference persisted when the subjects who were hospitalized with COVID were excluded meaning that even those with mild disease had brain shrinkage. When those who were hospitalized with COVID were compared to non-hospitalized COVID patients, those with the more severe infections had greater brain shrinkage.

Anosmia, or loss of the ability to smell, is commonly seen during COVID, and has been thought to be due primarily to direct viral infection of olfactory sensors in the nose.  The sense of smell usually returns. This study showing evidence of shrinkage in olfactory pathways in the brain during COVID raises several interesting questions. Is this because the COVID virus has migrated to the brain along the various olfactory pathways, or is it just a reflection of disuse atrophy? Will this shrinkage be reversed with the passage of time or will it be permanent? How will this effect memory and will there be a greater risk of dementia in patients who have had COVID? I don’t think we know the answer to any of these questions yet, but this study should encourage new investigations in this area.