One of the more mysterious side effects of COVID-19 has been what many have dubbed "brain fog."
"I’d say the overall most common characteristics of this are described as difficulty multi-tasking, focusing and really functioning at the same high level cognitively - which is broad, but functioning at their pre-COVID cognitive level," said Jeff Clark, a medical student who is a member of the Neuro COVID-19 clinical team at Northwestern Memorial Hospital studying the neurological effects of the disease.
He said that many patients in their clinic report that symptoms can last for as long as four to five months, with most of these "long-haulers" reporting some type of brain fog symptom.
"I would say on average that patients are noticing that brain fog can last on the order of several months," he explained.
Another possible neurological symptom in COVID patients is the loss of smell, although Clark told KCBS Radio's "Ask An Expert" it isn't clear if the loss of smell is actually originating in the nervous system or elsewhere.
"Anatomically, basically what you’re looking at is that particles have to access the olfactory nerve to be sensed as smell," through a connection between the nasal cavity, epithelial cells lining the tissue and the olfactory nerve, said Clark.
"So it is a way to access the brain and it is more exposed than, for example, the blood-brain barrier…so it is plausible that there could be introduction of the virus particles themselves into this nervous tissue, but the nervous tissue also depends on the epithelial lining of the nasal cavity to function."
Therefore, the loss of smell could come from viral damage to the neurons, or damage to the nasal cavity.
He explained that loss of smell has been noticed in other respiratory diseases before, but is more prominent with COVID-19.
"There is actually evidence that the SARS-CoV-2 virus can invade the nervous system," he said, citing a German study that looked at autopsies of deceased COVID-19 patients and found viral particles in the cranial nerves.
But there is not a clear link between those nerve cells and COVID-19 symptoms, he added.
"The perception of this in general is that while neural invasion can occur, it really doesn’t seem to be the most prominent or leading hypothesis for the neurological manifestations that we’re seeing."
Clark said further study will be needed to determine exactly what is causing brain fog and loss of smell.
Related
