Brain Damage from Covid Contributing to Loss of Smell?
I suspected brain damage was the cause of the loss of taste and smell and unfortunately I was correct. I didn’t want to come out and say it until we had some data.
My personal Covid story is that I knew I had covid in late 2021 when I could no longer smell coffee. Not only could I NOT smell it, it tasted like bitter mud water. I also could not smell my essential oils that I use to calm my nervous system. I was devastated at the time. It set off a panic inside me that I can’t explain. Fortunately my sense of smell and taste has mostly recovered over time.
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This past month a study was published in Nature that is the first longitudinal imaging study comparing the brain scans acquired from individuals BEFORE and AFTER SARS-CoV-2 infection, to those scans from a well-matched control group.
It also is one of the largest COVID-19 brain imaging studies to data, with 785 participants including 401 individuals infected by SARS-CoV-2.
Study participants were aged 51–81, they were imaged twice, with 141 days on average separating their diagnosis and second scan, and included 384 controls.
Their longitudinal analyses revealed a significant, deleterious impact associated with SARS-CoV-2. This impact could be seen mainly in the limbic and primary and secondary olfactory cortical system.
The limbic system is the part of the brain involved in our behavioral and emotional responses, especially when it comes to behaviors we need for survival.
The olfactory system is responsible for sense of smell.
They found reduced gray matter in several regions associated with olfaction, consistent with symptoms of prolonged loss of smell.
This study showed significant cortical gray matter loss, equivalent to nearly 10 years of aging!
Even those with no or only mild symptoms of Covid19 showed significant changes. Cortical damage seemed to occur regardless of disease severity, age, or sex.
Brain atrophy (shrinkage) was localized to a few regions: mainly limbic and olfactory. However, the increase in cerebrospinal fluid volume and the decrease of whole brain volume suggests additional global, diffuse loss of grey matter.
Between the pre-Covid scan and the post-Covid scan, participants experienced a 0.7% reduction in overall cortical gray matter on average, compared to the control group.
Normal middle-aged and beyond brain matter loss is only 0.2% to 0.3% per year.
Cortical thickness was also reduced was in an associated region called the orbitofrontal cortex. The OFC receives inputs from the primary olfactory cortex and is commonly referred to as the secondary olfactory cortex.
The researchers also speculate that the loss of volume in these olfactory regions may be a matter of “use it or lose it” and perhaps the blame should be laid on the widespread damage to the olfactory epithelium that disrupts neural pathways and impairs function.
As for the limbic system: adjacent regions that play an important role in the hippocampal memory system were involved in the loss which could signify future memory impairments. Other adjacent regions responsible for emotional processing and regulation were also involved.
All of the damage may be a consequence of a robust immune response occurring all around the brain.
Damage to brain cells cannot be reversed. We can mitigate the inflammation, however. More on that in future posts in this series.1
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Early on in the pandemic a study came out looked at patients with new neurological complications during hospitalization, who survived, as compared to COVID-19 survivors without neurological complications hospitalized during the same period.
Overall, 346/382 (91%) patients had at least one abnormal outcome: 56% had limited ADLs, 50% impaired cognition, 47% could not return to work and 62% scored worse than average on ≥1 Neuro-QoL scale (worse anxiety 46%, sleep 38%, fatigue 36%, and depression 25%).
“Conclusions: Abnormalities in functional outcomes, ADLs, anxiety, depression and sleep occurred in over 90% of patients 6-months after hospitalization for COVID-19.”2
How long do Covid-19-related neurological complications last?
Another recent study interviewed previously hospitalized Covid-19 patients three months after infection and then again one year later.
76 patients completed a 3-month and 1-year follow-up. Patients were 54 (47-64) years old and 59% were male. New and persistent neurological disorders were found in 15% (3 months) and 12% (10/81; 1 year).
While some showed cognitive improvement, 73% showed no difference between three-months and a year.
Neurological symptoms at 1-year follow-up were reported by 48/81 (59%) patients, including fatigue (38%), concentration difficulties (25%), forgetfulness (25%), sleep disturbances (22%), myalgia (muscle pain) (17%), limb weakness (17%), headache (16%), impaired sensation (16%) and hyposmia (loss of smell) (15%).
Again, the prevalence of these symptoms did not correlate with disease severity.
Clearly, neurological sequelae from Covid19 may persist after recovery from acute infection, regardless of severity of disease.
“Conclusion: Our data indicate that a significant patient number still suffer from neurological sequelae including neuropsychiatric symptoms 1 year after COVID-19 calling for interdisciplinary management of these patients.”3
I will update this blog series as new studies come out, but for now my hypothesis was correct. Actual widespread damage to the olfactory epithelium disrupts neural pathways and impairs function upstream, and potentially direct damage to the primary and secondary olfactory centers of the brain are responsible for loss of smell (hyposmia) post-Covid.
In addition there are other regions of the brain damaged leading to a wide range of neurological symptoms.
Be sure to check out the entire series: The Long Haul & my podcast episode all about Long Haulers:
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