a new study suggests. However, the research also showed there was no excess risk of these neurologic disorders following COVID than other respiratory infections such as influenza or community-acquired bacterial pneumonia.
Considering these results, study investigator Pardis Zarifkar, MD, department of neurology, Rigshospitalet, Copenhagen University Hospital, urged doctors to “keep an eye on” COVID patients and use “a critical mindset” if these patients present with neurologic issues.
“They should consider whether the patient’s condition is something new or if there were already signs and symptoms before they had COVID-19,” she said.
The findings were presented at the 2022 congress of the European Academy of Neurology and published online in Frontiers in Neurology.
‘Surprising’ increased risk
Previous research shows more than 80% of patients hospitalized with COVID-19 have neurologic symptoms including anosmia, dysgeusia, headache, dizziness, memory and concentration difficulties, fatigue, and irritability.
However, it’s unclear whether COVID-19 affects the risk for specific neurologic diseases and if so, whether this association differs from other respiratory infections.
From electronic health records covering about half the Danish population, researchers identified adults who were tested for COVID-19 or diagnosed with community-acquired bacterial pneumonia from February 2020 to November 2021. They also flagged individuals with influenza in the corresponding prepandemic period (February 2018–November 2019).
Dr. Zarifkar noted influenza A or B and community-acquired bacterial pneumonia are two of the most common respiratory tract infections.
The investigators tracked neurologic diseases up to 12 months after a positive test. They looked at two neurodegenerative diseases, Alzheimer’s disease and Parkinson’s disease, as well as cerebrovascular disorders including ischemic stroke, intracerebral hemorrhage, and subarachnoid hemorrhage.
The study included 43,262 individuals with a positive COVID test without a history of influenza A/B in the past year and 876,356 without a positive COVID test. It also included 1,474 individuals with community-acquired pneumonia without a history of COVID and 8,102 with influenza A or B.
“We wanted to investigate whether COVID-19 is really that much worse than all these other common respiratory infections that we have had for ages and see every single year,” said Dr. Zarifkar.
After 12 months, the relative risk for Alzheimer’s disease was 3.4 (95% confidence interval, 2.3-5.1) in the COVID-positive group versus the COVID-negative group. The risks were greater among inpatients versus outpatients.
These results were rather unexpected, said Dr. Zarifkar. “I would have expected a small increase, but the extent of the increase was quite surprising.”
However, there was no difference when comparing the COVID-19 group with the influenza or bacterial pneumonia groups, which Dr. Zarifkar said was “very reassuring.”
The findings were similar for Parkinson’s disease, where there was a 2.2-fold increased risk of a Parkinson’s disease diagnosis within the first 12 months in COVID-positive individuals, compared with COVID-negative people (RR, 2.2; 95% CI, 1.5-3.4). Again, there was no excess risk, compared with influenza or bacterial pneumonia.
Potential mechanisms
Dr. Zarifkar believes a “constellation” of factors may explain higher risks of these diagnoses in COVID patients. Part of it could be a result of neuroinflammation, which can lead to a toxic accumulation of beta amyloid in Alzheimer’s disease and alpha-synuclein in Parkinson’s disease.