Researchers from the National Institute of Neurological Disorders and Stroke studying the brains of patients who died from COVID-19, “consistently” found microvascular damage—but no signs of COVID-19 infection. Of the 19 patients in the study, 14 had chronic illnesses, including diabetes mellitus and hypertension, and 11 had ben found dead or had died unexpectedly. Of the 16 with available medical histories, one had delirium and the others had respiratory or unknown symptoms. Two had pulmonary embolism.
Patients with COVID-19 often have neurological problems, such as headaches, delirium, and dizziness. Some have strokes. Several studies have shown that COVID-19 can cause inflammation and blood vessel damage, but the precise mode of action is still unclear. In this study, the researchers used a magnetic resonance imaging (MRI) scanner 4 to 10 times more sensitive than most MRI scanners to examine samples of the olfactory bulbs and brainstems from the samples.
In 9 patients, the MRI scan showed punctate hyperintensities (bright spots representing areas of microvascular injury and fibrinogen leakage) that often indicate inflammation. In 10 brains, they found punctate hypointensities (dark spots) that corresponded to congested blood vessels, with surrounding areas of fibrinogen leakage and relatively intact vasculature. Areas of linear hypointensities (dark spots) were interpreted as microhemorrhages.
Using the scans as a guide, the researchers examined the spots more closely under a microscope. They found that the bright spots contained blood vessels that were thinner than normal and sometimes leaked blood proteins into the brain. This, the researchers say, seemed to trigger an immune reaction. The spots were surrounded by T cells from the blood and the brain’s own immune cells. In contrast, the dark spots contained clotted and leaky blood vessels but no immune response.
Moreover, although they used several methods for detecting genetic material or proteins from SAS-CoV-2, they found none. It’s possible, the researchers say, that the virus was cleared by the time of death or that viral copy numbers were undetectable by their assays.
We were completely surprised,” said Avindra Nath, MD, NINDS clinical director. “Originally, we expected to see damage that is caused by a lack of oxygen. Instead, we saw multifocal areas of damage that is usually associated with strokes and neuroinflammatory diseases.”
In future, Nath says, they plan to study how COVID-19 harms the blood vessels and whether that produces some of the short- and long-term symptoms seen. “We hope these results will help doctors understand the full spectrum of problems patients may suffer so that we can come up with better treatments.”