A new Danish study found COVID-19 outpatients had a higher risk of being diagnosed with Parkinson’s, Alzheimer’s, stroke and bleeding into the brain when compared with COVID-19 negative patients, but most neurological disorders were not more frequent after COVID-19 than after other respiratory infections, according to a recent study published in Frontiers in Neurology this June.
“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 Dr. Pardis Zarifkar, member of the Department of Neurology at Rigshospitalet hospital in Copenhagen, Denmark.
“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 study, which was recently presented at the 8th European Academy of Neurology Congress, found 43,375 individuals tested positive for COVID-19 while 876,356 individuals tested negative for the disease out of a total of 919,731 participants.
The study used electronic health records that covered approximately 50% of Denmark’s population, which has an estimated population of 3 million.
The study analyzed those who tested positive for COVID-19 and bacterial pneumonia in hospital-based facilities between February 2020 and November 2021, as well as reviewed influenza patients from the corresponding pre-pandemic period between February 2018 and November 2019.
Out of the 43,375 patients who tested positive for COVID-19, 35,362 were outpatients while 8,013 were hospitalized.
The researchers found the outpatients who tested positive for COVID-19 had a 3.5 times the risk of being diagnosed with Alzheimer’s disease, 2.6 times increased risk with Parkinson’s disease, 2.7 times increased risk with ischemic stroke and 4.8 times increased risk with intracerebral hemorrhage, which is bleeding in the brain.
But when the researchers compared the relative risk of neurological disorders with other respiratory illnesses, such as influenza, the increased risk of most neurological diseases was not higher in COVID-19-positive patients compared to those diagnosed with other respiratory illnesses – with one exception.
The researchers found the risk for ischemic stroke increased among COVID-19 hospitalized patients when compared to inpatients with influenza.
The study was limited because it did not account for potential confounding variables like socioeconomic, lifestyle, pre-existing comorbidities and length of hospitalization.
Although the study included a large population, it was only able to review a subset of the country’s absolute number of tested individuals as only COVID-19 tests performed in the hospital facilities are registered in the Danish electronic health record system that the study used to analyze the records.
“While the risk of ischemic stroke was increased with COVID-19 compared to influenza, reassuringly, most neurological disorders do not appear to be more frequent after COVID-19 than after influenza or community-acquired bacterial pneumonia,” the researchers concluded.
“Frequencies of multiple sclerosis, myasthenia gravis, Guillain-Barré syndrome and narcolepsy did not differ after COVID-19, influenza and bacterial pneumonia,” the study added.
“These findings will help to inform our understanding of the long-term effect of COVID-19 on the body and the role that infections play in neurodegenerative diseases and stroke,” Zarifkar said.