Covid-19 positive outpatients are at increased risk of neurodegenerative disorders compared to individuals who tested negative for the virus, a new study presented at the 8th Congress of the European Academy of Neurology.
The study, which analyzed the health records of more than half of the Danish population, found that those who had tested positive for Covid-19 had a higher risk of suffering from the disease. Alzheimer’s, Parkinson’s disease and the ischemic stroke.
Of the 919,731 individuals who were tested for Covid-19 within the study, the researchers found that the 43,375 people who tested positive had a 3.5 times greater risk of being diagnosed with Alzheimer’s disease, 2.6 times with Parkinson’s disease, 2.7 times with ischemic stroke and 4.8 times higher with intracerebral hemorrhage (bleeding in the brain).
While neuroinflammation may contribute to the accelerated development of neurodegenerative disorders, the authors also highlighted the implications of the scientific approach to long-term sequelae after Covid-19.
The study looked at inpatients and outpatients in Denmark between February 2020 and November 2021, as well as flu patients from the corresponding pre-pandemic period. The investigators used statistical techniques to calculate relative risk, and the results were stratified by hospitalization status, age, gender, and comorbidities.
Pardis Zarifkar, lead author of the Department of Neurology of Rigshospitalet in Copenhagen, Denmark, explains that “more than two years after the start of the Covid-19 pandemic, the precise nature and course of the effects of this disease on neurological disorders remain uncharacterized. Previous studies have established an association with neurological syndromes, but whether Covid-19 also influences the incidence of specific neurological diseases and whether it differs from other respiratory infections is unknown so far.”
However, the increased risk of most neurological illnesses was no greater in Covid-19-positive patients than in people who had been diagnosed with influenza or other respiratory illnesses. Patients with Covid-19 did have a 1.7 times higher risk of suffering an ischemic stroke compared to patients older than 80 years with influenza and bacterial pneumonia.
The frequency of other neurodegenerative diseases, such as multiple sclerosis, myasthenia gravis, Guillain-Barré syndrome, and narcolepsy, did not increase after Covid-19, the flu, or pneumonia.
“We found support for a higher risk of being diagnosed with neurodegenerative and cerebrovascular disorders in Covid-19 positive patients compared to Covid negative patients, which should be confirmed or refuted by large registry studies in the near future. Reassuringly, apart from ischemic stroke, most neurological disorders do not appear to be more common after COVID-19 than after influenza or community-acquired bacterial pneumonia,” adds Pardis Zarifkar.
“These findings will help to better understand the long-term effect of Covid-19 on the body and the role that infections play in neurodegenerative diseases and stroke.”