Does getting COVID19 shrink your brain?

Does getting COVID19 shrink your brain?  A paper from last Thursday’s Nature says yes.  Not only that, but it slows you mentally. Here’s a link: https://www.nature.com/articles/s41586-022-04569-5.pdf.   and a reference: Nature vol. 604 pp. 697 – 707 ’22.

Here’s what they did.  Take 785 people over 50 from England. Have 401 get infected with the pandemic virus, after obtaining MRI scans, all sorts of data including mental function about them.   Then repeat the MRI and mental tests  4 – 5 months after the infection.  Compare the two groups and there’s your answer.

The moral among you must be wondering how they ever got this past an Institutional review board.  It didn’t.  This was an experiment of nature on participants in the UK Biobank — https://en.wikipedia.org/wiki/UK_Biobank.  Starting in 2006 and ending in 2010 some 100,000 people (ages 40 – 69 on entry) from the United Kingdom (UK) were intensively studied (they donated urine, saliva and blood, filled out questionnaires, and consented to access to their electronic health records).   Planned follow up is 30 years.  All this before we had any idea about the pandemic to hit us in 2020.

Obviously the control group without infection, must be as similar as possible to the infected group and I think the authors tried their hardest.  Even so the control group was a bit older, and the infected group had slightly lower cognitive abilities.

The average time between the two scans was 3 years.  The average time from COVID19 to the second scan was 141 days.  The scans were done before Omicron hit.  Even so only 15/401 had to be hospitalized.  This is consistent with the mildness of the pandemic presently.  On 9 April 22 Shanghai reported some 23,000 positive PCR tests (for Omicron), but only one thousand or so were symptomatic.   Excluding the 15 from analysis didn’t change the result.  I’ve heard from clinicians, that the severely ill are usually obese.  This is partly true for the 15 hospitalized (average Body Mass Index 29.3) vs. the 386 not hospitalized (BMI – 26.6).

So the clickbait is that being infected with the virus shrinks your brain. But does it? It is stated that there was a decrease in thickness of the cerebral cortex (the gray matter on the surface of the brain) concerned with smell and taste.

The decreases were minimal.  Have a look at figure 1a p. 701.  The changes between scans are plotted vs. age, and separately for cases and controls. As we get older the brain shrinks.  This was true for both patients and the controls, but the patients showed more shrinkage (measured by the change between successive MRIs).

What sort of shrinkage in the thickness of he cerebral cortex are we talking about here?  At most 3% and usually under 2%.  But 3% of what?  Most estimates of the thickness of the human cerebral cortex place it around 2 – 3 millimeters (range 1 to 5 millimeters).  So I got out a clear plastic ruler and found that 1 milliMeter is about the thickness of a penny?  Are they really saying that the MRI can measure thickness differences of 2 – 3% of something only 2 – 3 millimeters.

It gets worse.  Most of us have seen MRI pictures by now.  If you look closely, you’ll see that they are slices made of pixels.  These are computed slices of 3 dimensional cubes (voxels).  And what dear reader is the size of an MRI voxel — around 1 x 1 x 1 milliMeters.  So they are measuring cortical thickness with a rather blunt instrument which is 30 – 50% the size of cortical thickness.  Do you think, even with averaging of hundreds of people, that they can pick up a change in cortical thickness of several percent in something so small.

I don’t, and am amazed that the reviewers let them get away with this.

The cognitive changes are on much better ground.  But that’s for the next post.  This post is long enough.

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Comments

  • Richard Sherry  On May 2, 2022 at 10:14 pm

    You are quite right to be skeptical about these morphological results. As a neuroradiologist I’d be keen to see some of the imaging used for making these measurements. In my own experience I think I’d be lucky to confidently identify a 30% reduction in cortical thickness, either visually or by measurement. There are so many confounding variables, not the least of which is the accuracy and reproducibility of the electronic calipers used to make these measurements. For structures under 10mm my own experience is the margin of error is usually in the 10-15% range at best. Can discuss more offline if interested.

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