What are the impacts of COVID-19 and other respiratory-based diseases on neurological processes? A new observational study assesses the likelihood of Alzheimer’s, Parkinson’s, and stroke in people who contract COVID-19 as well as influenza and pneumonia.
As we learn more about the aftereffects of COVID-19, it’s become clear that infection can result in diseases and conditions that impact multiple organs, including the brain. But do neurological and cerebrovascular conditions occur at higher rates in people who get COVID-19 compared with those who suffer a bout of influenza or bacterial pneumonia? A team of scientists conducted an observational study in order to find out.
The study, recently published in Frontiers in Neurology and presented at the 8th European Academy of Neurology Congress, was conducted by a team based out of Copenhagen University Hospital and the University of Copenhagen in Denmark. Examining the electronic health records of more than 919,000 people who had been tested for COVID-19 as well as those of people diagnosed with influenza or pneumonia, the scientists were able to calculate the frequency of Alzheimer’s disease, Parkinson’s disease, ischemic stroke, and intracerebral hemorrhage in these various cohorts.
Individuals who tested positive for COVID-19 experienced Alzheimer’s disease 3.5 times more frequently (RR = 3.5; 95% CI: 2.2-5.5) than people who were COVID-negative. They were diagnosed with Parkinson’s disease 2.2 times more frequently (RR = 2.6; 95% CI: 1.7-4.0); ischemic stroke 2.7 times more frequently, (RR = 2.7; 95% CI: 2.3-3.2); and intracerebral hemorrhage 4.8 times more frequently (RR = 4.8; 95% CI: 1-8-12.9).
Compared with individuals who had been diagnosed with influenza or bacterial pneumonia, however, COVID-positive patients did not experience neurological disorders more frequently, with the exception of ischemic stroke. Among the 8013 people who tested positive for COVID-19, the risk of stroke was heightened compared with those who had influenza (RR = 1.7; 95% CI: 1.2-2.4) or bacterial pneumonia (RR = 2.7; 95% CI: 1.2-6.2).
This higher rate of stroke may be because COVID-19 is known to induce an especially aggressive inflammatory response in the body, the study’s authors say. “An unwanted consequence of this inflammatory response is a hypercoagulable state, which increases the risk of thromboembolisms and, thus, ischemic stroke,” Pardis Zarifkar, MD, a neurologist at Copenhagen University Hospital and an author of the study, told Contagion. “By nature, some microorganisms lead to stronger immune responses than other microorganisms.”
Stroke risk was particularly heightened in middle-aged COVID-19 patients, but Zarifkar and her colleagues acknowledge that as the main stroke risk factor is age, and older patients tend to have comorbidities that lead to poorer COVID-19 outcomes in general, the rate of stroke in middle-aged people with COVID-19 may seem more pronounced by comparison.
Although Alzheimer’s and Parkinson’s diseases generate physiological changes years before symptoms present, being infected with COVID-19 and/or being hospitalized may cause physical deterioration that allows for an earlier diagnosis of these neurological conditions. Simply monitoring patients closely also may enable physicians to discern neurological problems. “[W]hile biological mechanisms may account for a subsection of the increases, we expect that a decompensation of the symptoms after infection and the scientific communities’ focus on COVID-19 survivors may have led to earlier diagnosis of diseases already in the making,” Zarifkar said.
COVID-19 causes Long COVID symptoms, which can include brain fog and fatigue, in a significant percentage of patients; because of this, Zarifkar and her team currently are conducting clinical studies that hopefully will enable a deeper understanding of cognitive impairment and mental health challenges in people hospitalized for conditions including, but not limited to, COVID-19.