Thread by @ZdenekVrozina

New brain MRI study (2025): Post-COVID patients show measurable structural changes - even without hospitalization.
Participants were not selected for having Long COVID!
What was found, why it matters, and how this fits into what we know about hypothalamus-related circuits. 🧵

COVID-19 doesn’t always leave visible scars - but in the brain, it leaves measurable traces.
A new multimodal MRI study (N=76 post-COVID vs N=51 controls) shows focal loss in key subcortical and limbic areas.

That includes:
Right amygdala, hippocampus, thalamus
Right putamen, caudate, pallidum
These aren’t random.
They’re deep grey structures involved in motivation, memory, alertness - all connected with hypothalamus-mediated homeostasis.

The study used:
structural T1 MRI
diffusion MRI (white matter microstructure)
resting-state fMRI (connectivity)
arterial spin labeling (perfusion)

And crucially:
Participants were not selected for having Long COVID!

That’s key.
All 76 had PCR-confirmed COVID-19.
But they weren’t selected based on symptoms.
59 of them later reported post-COVID symptoms.
So any MRI abnormalities were found regardless of symptom status.

Even non-hospitalized post-COVID patients (NHP; N=46) had statistically significant brain changes compared to healthy controls:
Reduced volume in right thalamus, amygdala, caudate
White matter disruption (eg left uncinate fasciculus)

Now let’s be clear:
The study found consistent, localized changes in brain regions linked to fatigue, memory, sleep, and mood regulation.

How big were the changes?
Average group differences were small - a few percent in volume.
But they were statistically significant even after FDR correction.

Which tells us something important

If every non-hospitalized patient had changes, the group differences would be huge.
If none did, there’d be no statistical signal.

So the most likely interpretation?
Somewhere between 30–60% of NHPs had measurable structural or microstructural changes (eg amygdala volume, FA in uncinate).

But here’s the catch.
The study didn’t do subject-level classification.
We can’t say who’s affected and who’s not.
We only know that as a group, post-COVID brains differ - even without severe illness.

That nuance matters:
Some NHPs were clearly affected.
Some were likely not - otherwise, group averages would differ more.

This also means symptoms ≠ required for damage.
And lack of symptoms ≠ guarantee of normal brain structure.

In the hospitalised subgroup, functional changes were more pronounced - particularly in default mode-insula-caudate connectivity.
But even NHPs showed measurable alterations in limbic white matter, consistent with inflammation or axonal stress.

So, to sum up:
No global brain shrinkage
But focal reductions in thalamus, amygdala, hippocampus
White matter injury in uncinate & cingulum
Changes present even in non-hospitalized
Not all affected - but many are

This fits with what we know about hypothalamus-centered systems:
Hypothalamus integrates signals from limbic and subcortical regions
Fatigue, sleep disruption, mood blunting = plausible outcomes
Damage here can dysregulate core homeostasis

Protect your hypothalamus.
Protect your brain.

Mishraa et al., 2025, Multimodal MRI Reveals Consistent Basal Ganglia and Limbic System Alterations in COVID-19 Survivors @szupraha @ZdravkoOnline
.medrxiv.org/content/10.110…

This is a preprint (Mishraa et al., 2025, medRxiv) and has not yet been peer-reviewed.
Still, its methods are solid, and the findings are consistent with prior studies, including UK Biobank (Nature, 2022).