Until now, the neurological manifestations of COVID-19 have been believed to be a result of direct damage to nerve cells. However, a new study suggests that the virus might actually damage the brain’s small blood vessels rather than nerve cells themselves.
The findings add further weight to previous research into neurological complications from COVID-19, according to Anna Cervantes, MD. Dr. Cervantes is assistant professor of neurology at the Boston University and has been studying the neurological effects of COVID-19, though she was not involved in this study. “I can tell from my personal experience, and things we’ve published on and the literature that’s out there – there are patients that are having complications like stroke that aren’t even critically ill from COVID. We’re seeing that not in just the acute setting, but also in a delayed fashion. Even though most of the coagulopathy is largely venous and probably microvascular, this does affect the brain through a myriad of ways,” Dr. Cervantes said.
The research was published online Jan. 12 in the New England Journal of Medicine. Myoung‑Hwa Lee, PhD, was the lead author.
The study included high resolution magnetic resonance imaging and histopathological examination of 13 individuals with a median age of 50 years. Among 10 patients with brain alterations, the researchers conducted further studies in 5 individuals using multiplex fluorescence imaging and chromogenic immunostaining in all 10.
The team conducted conventional histopathology on the brains of 18 individuals. Fourteen had a history of chronic illness, including diabetes, and hypertension, and 11 had died unexpectedly or been found dead. Magnetic resonance microscopy revealed punctuate hypo-intensities in nine subjects, indicating microvascular injury and fibrinogen leakage. Histopathology using fluorescence imaging showed the same features. Collagen IV immunostaining showed thinning of the basal lamina of the endothelial cells in five patients. Ten patients had congested blood vessels and surrounding fibrinogen leakage, but comparatively intact vasculature. The researchers interpreted linear hypo-intensities as micro-hemorrhages.
The researchers found little perivascular inflammation, and no vascular occlusion. Thirteen subjects had perivascular-activated microglia, macrophage infiltrates, and hypertrophic astrocytes. Eight had CD3+ and CD8+ T cells in the perivascular spaces and in lumens next to endothelial cells, which could help explain vascular injury.
The researchers found no evidence of the SARS-CoV-2 virus itself, despite efforts using polymerase chain reaction with multiple primer sets, RNA sequencing within the brain, or RNA in situ hybridization and immunostaining. Subjects may have cleared the virus by the time they died, or viral copy numbers could have been below the detection limit of the assays.
The researchers also obtained a convenience sample of subjects who had died from COVID-19. Magnetic resonance microscopy, histopathology, and immunohistochemical analysis of sections revealed microvascular injury in the brain and olfactory bulb, despite no evidence of viral infection. The authors stressed that they could not draw conclusions about the neurological features of COVID-19 because of a lack of clinical information.
Dr. Cervantes noted that limitation: “We’re seeing a lot of patients with encephalopathy or alterations in their mental status. A lot of things can cause that, and some are common in patients who are critically ill, like medications and metabolic derangement.”
Still, the findings could help to inform future medical management. “There’s going to be a large number of patients who don’t have really bad pulmonary disease but still may have encephalopathy. So if there is small vessel involvement because of inflammation that we might not necessarily catch in a lumbar puncture or routine imaging, there’s still somebody we can make better (using) steroids. Having more information on what’s happening on a pathophysiologic level and on pathology is really helpful.”
The study was supported by internal funds from the National Institute of Neurological Disorders and Stroke. Dr. Cervantes has no relevant financial disclosures.