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Magnetic resonance spectroscopy reveals neurochemical abnormalities that shed light on how the virus impacts the brain.
COVID-19-positive patients who have neurological symptoms associated with the virus also show evidence of some of the same metabolic disturbances – with some differences – that appear in the brains of patients who suffer oxygen deprivation.
In one of the first studies to use spectroscopic imaging to assess COVID-19 neurological injuries, a team from Massachusetts General Hospital used magnetic resonance spectroscopy (MRS) to examine specific types of damage that can distinguish COVID-19-related brain injury. They published their findings in the American Journal of Neuroradiology.
Even though COVID-19 is largely considered to be a respiratory disease, the impact on the brain is also well recognized. So far, it is believed the virus’s primary effect on the brain comes through hypoxia, but the severity of neurological symptoms does vary from the temporary loss of smell to dizziness, confusion, seizures, and stroke.
It was these symptoms that sparked the team’s interest, said senior author Eva-Maria Ratai, Ph.D., associate professor of radiology at the Harvard Medical School.
“We were interested in characterizing the biological underpinnings of some of these symptoms,” she said. “Moving forward, we are also interested in understanding long-term lingering effects of COVID-19, including headaches, fatigue, and cognitive impairment. So-called ‘brain fog’ and other impairments that have been found to persist long after the acute phase.”
The team opted for MRS, sometimes referred to as virtual biopsy, in this study because it does a better job of characterizing pathological processes, such as neuronal injury, inflammation, demyelination, and hypoxia. Consequently, they asserted, it could be used as a disease- and therapy-monitoring tool.
Using 3T MRS, the team examined six patients’ brains – including three COVID-19-positive patients – for neurochemical abnormalities. They found that patients positive for the virus showed N-acetyl-aspartate (NAA) reduction, choline elevation, and myo-inositol elevation. These findings were similar to what has been seen in other non-COVID-19 patients who exhibit white matter abnormalities (leukoencephalopathy) after hypoxia.
Specifically, the team found MRS showed particularly elevated lactate in one of the COVID-19-positive patients who had the most severe white matter damage, including necrosis and cavitation. This elevation is another sign of hypoxia, the team said. In addition, two of the three COVID-19-positive patients were intubated at the time of imaging, and one had COVID-19-associated necrotizing leukoencephalopathy. Another had experienced a recent cardiac arrest, and structural MR revealed subtle white matter changes. The third COVID-19-positive patient had neither clear encephalopathy nor recent cardiac arrest.
Among the non-COVID-19 control group, one patient exhibited white matter damage caused by post-hypoxic leukoencephalopathy, and another had sepsis-related white matter damage. The third participant was a normal, age-matched healthy volunteer.
Even with these findings, unknowns still remain, the team said.
“A key question is whether it is just the decrease in oxygen to the brain that is causing these white matter changes or whether the virus is itself attacking the white matter,” said Otto Rapalino, M.D., MGH neuroradiologist and study co-first author with postdoctoral research fellow Akila Weerasekera, Ph.D.
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