New research presented recently at the European Academy of Neurology Congress in Vienna has found an increased risk of several neurological disorders in patients following a bout of COVID-19. The study found the risk of Alzheimer’s, Parkinson’s and stroke all increased in COVID-positive subjects compared to those uninfected.
“More than two years after the onset of the COVID-19 pandemic, the precise nature and evolution of the effects of COVID-19 on neurological disorders remained uncharacterized,” said lead author on the new study, Pardis Zarifkar, from the Copenhagen University Hospital. “Previous studies have established an association with neurological syndromes, but until now it is unknown whether COVID-19 also influences the incidence of specific neurological diseases and whether it differs from other respiratory infections.”
The researchers analyzed electronic health records from almost half of Denmark’s total population, spanning 2020 and 2021. Across the study period those who tested positive for COVID-19 were found to be 3.5 times more likely to be diagnosed with Alzheimer’s disease; 2.6 times more likely to be diagnosed with Parkinson’s; 4.8 times more likely to experience bleeding in the brain; and 2.7 times more likely to develop ischemic stroke.
Zarifkar does note the increased risk of these neurological conditions following COVID-19 does mirror what has previously been reported following cases of influenza or bacterial pneumonia. However, due to the sheer prevalence of COVID-19 infections, it is likely baseline rates of these neurodegenerative diseases will rise around the world over the coming years.
“We found support for an increased risk of being diagnosed with neurodegenerative and cerebrovascular disorders in COVID-19 positive compared to COVID-negative patients, which must be confirmed or refuted by large registry studies in the near future,” added Zarifkar. “Reassuringly, apart for ischemic stroke, most neurological disorders do not appear to be more frequent after COVID-19 than after influenza or community-acquired bacterial pneumonia.”
For decades researchers have seen a correlation between certain viral infections and neurodegenerative disease. Perhaps most well-known was the increase in rates of Parkinson’s disease following the Spanish Flu pandemic in the early 20th century.
Since the beginning of the pandemic in 2020 researchers have warned of potential spikes in conditions such as Parkinson’s, and this new data offers early signals these predictions may be coming true. Other more recent studies have started digging into exactly what mechanisms could be contributing to this increased risk of neurodegenerative disease following COVID-19.
For years the most prominent hypothesis to explain the link between viral infections and neurodegeneration has been that inflammation triggered by an infection may either initiate, or accelerate, the development of neurological disease. A review article published back in 2012 suggested repeated viral infections may increase this risk of neurological disease by activating a “cascade of events” corresponding with what is seen in the earliest stages of neurodegeneration.
“We suggest that neurodegeneration can be triggered and then propagated by repeated inflammatory reactions (such as local production of cytokines) over time,” the 2012 review indicated. “Indeed, there is evidence for both microglial and astrocytic (star-shaped glial cells in the brain) activation and reactions that track existing neuronal circuits in the CNS [central nervous system] and PNS [peripheral nervous system]. These inflammatory sequences combined with regional and cell type–dependent neuronal vulnerability could cause the specific structural and functional neurodegenerative patterns that define individual neurodegenerative diseases.”
A number of recent studies have found brain inflammation to be a characteristic of some COVID-19 infections. But it still isn’t clear how the virus may be causing this neuroinflammation or whether this autoimmune response will cause long-term problems.
Commenting on the new COVID-19 findings, Sara Imarsio from Alzheimer’s Research UK said it is important to remember that dementia-causing neurological diseases are caused by a constellation of factors, from genetic susceptibility to age and environment. So COVID-19 is potentially only playing a small role in a person’s total risk of developing these diseases.
Imarsio also pointed out a number of other factors could explain why rates of neurodegenerative disease are higher in those infected with COVID-19. And, it certainly is too soon to know the long-term impact of COVID-19 on certain brain diseases that can take decades to develop.
“Diseases like Alzheimer’s develop in the brain over many years and COVID-19 has only been present in Europe since early 2020,” added Imarsio. “It may be that people in the very early stages of Alzheimer’s are more susceptible to catching diseases like COVID-19. While the announcement of these findings is potentially concerning, we will need to see results of this study in a peer-reviewed publication before we can draw any real conclusions from this research.”
The new study was published in the journal Frontiers in Neurology.
Source: European Academy of Neurology