Viral infections can impact the brain, even if the virus has not directly infected brain tissue. For example, inflammation of the brain, or encephalitis, most often results from a viral infection.
These infections usually cause mild, flu-like symptoms, but when they affect the brain, the issues can be severe.
At around the same time as the 1918 flu pandemic, there was an epidemic of encephalitis lethargica, or “sleeping sickness.” Between 1917 and 1927, millions of people likely developed this issue worldwide. Many of the survivors experienced lasting behavioral changes and extreme lethargy. Some lived in catatonic states.
Previously, some researchers have observed a link between infections with SARS-CoV and MERS-CoV — the coronaviruses that cause SARS and MERS, respectively — and signs of damage within the central nervous system.
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The new coronavirus has also been associated with neurological symptoms. However, our understanding of the neurological consequences of COVID-19 remains in its early stages.
A recent report, led by experts from the Institute of Neurology at University College London, describes cases of delirium, brain inflammation, stroke, and nerve damage associated with COVID-19.
The authors say that their report, which is published in the journal Brain, provides a template to help researchers around the world improve the diagnosis and treatment of the neurological complications of COVID-19.
The study describes the experiences of 43 people with suspected or confirmed COVID-19 who were referred to the National Hospital for Neurology and Neurosurgery, in the U.K. The group had a wide age range of 16–85 years.
The study team analyzed both the clinical features and the results of brain scans and laboratory tests, and it is the first to have done so in this context.
The report details 10 cases of temporary brain dysfunction, or encephalopathies, with delirium. These patients were mostly over 50 and presented with confusion and disorientation, with one patient experiencing psychosis.
A further 12 patients experienced inflammation of the brain. The majority of these people experienced a rare disorder called acute demyelinating encephalomyelitis (ADEM), which is triggered by viral infections and leads to damage of the myelin sheaths around nerves.
The researchers note that ADEM is more common in children and that they typically see around one adult with the condition per month. During the period that the study was concerned with, this rate increased to one case per week. This is concerning, as ADEM can progress to multiple sclerosis.
The team also found reports of nerve damage. Specifically, there were seven reports of Guillain-Barré syndrome, a rare neurological disorder in which a person’s immune system attacks healthy nerve networks.
This syndrome is often associated with a prior infection and also involves damage to myelin.
The finding is consistent with a previous report, from Italy, of five cases of Guillain-Barré syndrome in COVID-19 patients.
“We identified a higher-than-expected number of people with neurological conditions such as brain inflammation, which did not always correlate with the severity of respiratory symptoms. We should be vigilant and look out for these complications in people who have had COVID-19.”
– Co-senior author Dr. Michael Zandi
The team also reported eight cases of stroke, which confirms previous findings. These cases are thought to result from the “sticky blood” found in COVID-19 patients.
The remaining patients had other neurological complaints, including dysfunction of the cranial nerve and a brain abscess.
Interestingly, some patients in the study did not experience any severe respiratory symptoms, making their neurological symptoms the first and major presentation of COVID-19.
The authors say that doctors should look out for possible neurological symptoms in people with suspected COVID-19.
“Doctors need to be aware of possible neurological effects, as early diagnosis can improve patient outcomes. People recovering from the virus should seek professional health advice if they experience neurological symptoms,” says co-lead author Ross Paterson, Ph.D.
In eight of the patients, the fluid that surrounds the brain and spinal cord was tested for the virus, and no evidence of it was found. This suggests that neurological symptoms of COVID-19 are not a result of a direct attack on the nervous system.
Understanding exactly how an infection with the new coronavirus causes these symptoms will require more research. However, it seems likely that the neurological consequences of COVID-19 result from an immune response gone awry, rather than the virus itself.
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