In an in-depth study of how Covid-19 affects a patient’s brain, researchers from the US National Institutes of Health (NIH) consistently spotted hallmarks of damage in tissue samples from deceased patients of the disease. This damage to tissue samples was caused by thinning and leaky brain blood vessels. Yet the researchers saw no signs of SARS-CoV-2 in the tissue samples. This suggests that the damage was not caused by a direct viral attack on the brain, NIH said in a statement on the research. The results were published as a correspondence in the New England Journal of Medicine.
“We found that the brains of patients who contract infection from SARS-CoV-2 may be susceptible to microvascular blood vessel damage. Our results suggest that this may be caused by the body’s inflammatory response to the virus” NIH quoted the study’s senior author Avindra Nath, clinical director at the NIH’s National Institute of Neurological Disorders and Stroke (NINDS), as saying.
Although Covid-19 is primarily a respiratory disease, patients often experience neurological problems including headaches, delirium, cognitive dysfunction, dizziness, fatigue, and loss of the sense of smell. The disease may also cause patients to suffer strokes.
Several studies have shown that the disease can cause inflammation and blood vessel damage. In one of these studies, researchers found evidence of small amounts of SARS-CoV-2 in some patients’ brains. Nevertheless, NIH said, scientists are still trying to understand how the disease affects the brain.
In this study, the researchers conducted an in-depth examination of brain tissue samples from 19 patients who had died after experiencing Covid-19 between March and July 2020. The patients died at a wide range of ages, from 5 to 73 years old. They died within a few hours to two months after reporting symptoms. Many patients had one or more risk factors, including diabetes, obesity, and cardiovascular disease. Three patients collapsed and died suddenly.
Initially, the researchers used a special, high-powered MRI scanner to examine samples of the olfactory bulbs and brainstems from each patient. These regions are thought to be highly susceptible to Covid-19. Olfactory bulbs control our sense of smell while the brainstem controls our breathing and heart rate. The scans revealed that both regions had an abundance of bright spots (called hyperintensities) that often indicate inflammation, and dark spots (called hypointensities) that represent bleeding.
The researchers then used the scans as a guide to examine the spots more closely under a microscope. They found that the bright spots contained blood vessels that were thinner than normal and sometimes leaking blood proteins, like fibrinogen, into the brain. This appeared to trigger an immune reaction. The spots were surrounded by T cells from the blood and the brain’s own immune cells called microglia. In contrast, the dark spots contained both clotted and leaky blood vessels but no immune response.
Source: NIH (US)