How this virus damages the brain and nerves is still not entirely clear. But as two doctors dedicated to the study of the nervous system, we wanted to find some answers.
Dr. Sanjay Gupta has been a practicing neurosurgeon for the past 20 years and has always been amazed at the amazing ways that the brain is protected by the body. A hard shell of bones, a bath of clear fluid and a barrier in the blood brain, which creates checkpoints before certain molecules are allowed to enter. It is our most important organ and more impermeable than many. And, nevertheless this virus is still able to settle in the central nervous system.
And Dr. Minali Nigam is a resident doctor created and chose to go into neurology, an area that connects the mind and body. Appearance small details such as the ability to raise an eyebrow can tell us which part of the nervous system is injured. There is a lot we don’t know about the brain, which means huge potential for our knowledge to grow.
Coronavirus also affects the brain and nerves
Among the most common neurological symptoms is loss of odor and taste, which may be the first clue that someone has Covid-19.
Other possible symptoms include headache, dizziness, loss of consciousness, weakness, seizures, paralysis, strokes and more.
We know that the virus spreads through particles in the air, so it first enters the body through the nose and mouth. When this happens, it is possible for the virus to then potentially cross the cribriform plate, the bone at the top of the nose, to reach the olfactory bulb that hosts the olfactory nerve and its branches. If the virus damages these nerves, a person may lose their sense of smell. If the virus directly invades the taste buds, it can prevent nerve fibers from transmitting signals to the brain and cause a person to lose their sense of taste.
Another hypothesis relates to a protein receptor called an angiotensin-converting enzyme – known as ACE2 – that is found in cells around the body in the lungs, kidneys, blood vessels, muscles, nose and mouth. In the nose and mouth, the virus is thought to bind to ACE2 receptors in sensory nerve cells and block these cells from facilitating smell and taste.
ACE2 also helps maintain blood pressure and protects the heart and brain from damage. Its role is to lower the levels of a molecule called angiotensin II. If angiotensin II levels build up, the blood vessels restrict and reduce blood flow to the organs, potentially damaging them.
Here is the most interesting thing we are starting to learn. Whether it’s the body or the mind, most of the symptoms don’t seem to come directly from the virus, but rather, the body’s excessive immune response to fighting the virus.
Give strokes, e.g.
When the virus attaches to ACE2 in the blood vessels, it triggers an immune response – sometimes called a cytokine storm. Too much inflammation can disrupt the body’s clotting system and form millions of small clots or several large clots. Along with higher levels of angiotensin II that restrict blood vessels, clots can block blood flow to the brain and lead to a stroke.
Some strokes are minor and patients may not notice they are having one. As people get older, multiple strokes can build up and cause memory loss or poor attention. Other patients recovering from Covid may show symptoms of their silent strokes such as depression, anxiety, insomnia or cognitive decline later in life, according to Fotuhi.
Too much inflammation can also break down the protective wall known as the blood-brain barrier and lead to swelling in the brain, seizures or spread of infection.
It is not clear why meningitis developed. But we know that meninges is a protective layer around the brain and spinal cord and is rich in blood vessels and ACE2. In theory, if the virus binds to ACE2 in the meninges, it can lead to significant venous damage and inflammation.
Some patients with the virus have also been found to have Guillain-Barre Syndrome, a nerve disorder that can lead to paralysis. Here, antibodies, formed in response to the virus, react to proteins found on the nerves, causing damage.
But it is important to remember that everyone responds to the virus differently.
“There are people who have a measured response to the virus and their immune system can handle it without overreacting,” Fotuhi said.
“Healthy asymptomatic people are those who have had enough immune response to destroy the virus without creating a cytokine storm or blood clots.”
How this happens sticks to two main mechanisms: direct viral invasion of the nervous system or damage by an overactive immune system.
Some neurological manifestations such as confusion or weakness may also be non-specific complications of critical illness that are not related to the actual virus.
“Neurological involvement appears to be a prominent feature of this coronavirus,” said Dr. Felicia Chow, a neuroinfectious disease expert at the University of California, San Francisco.
Or we may see more neurological complications with Covid simply because there are many more cases of Covid in general compared to previous coronavirus outbreaks.
Like what doctors see with Covid-19 and strokes.
“What has been reported so far is not really something we see in common with at least certain types of respiratory viruses,” she said. “But it’s hard to say with the still limited information we have. A much deeper dive is needed to understand the true neurological burden and sequelae of this pandemic.”
There are no major studies looking at Covid-related neurological symptoms, so doctors are now treating these symptoms as they do for patients who do not have the virus.
But small studies with a few hundred people have emerged. A consistent feature is that patients with risk factors such as high blood pressure, diabetes, and obesity who get Covid are at higher risk for severe outcomes, including neurological complications, than healthy, fit individuals.
That is why regular exercise, proper diet, proper sleep and stress reduction are still important during this pandemic. By maintaining an active, healthy lifestyle, patients who end up infected can “improve their likelihood of a faster and more favorable recovery,” Fotuhi said.
For doctors, patients with Covid may not be sick with the typical viral symptoms you expect such as cough or fever. Some patients seen in the emergency room showed only signs of a stroke. And brain symptoms may be the patient’s first and only symptoms. In some situations, blood thinners and steroids can be as important as anti-viral medications.
“Covid can have a lot of different faces,” Fotuhi said. “It’s important for people to appreciate it.”
And something we keep in mind while caring for patients.
When covering the pandemic as journalists and caring for Covid patients as doctors, we have learned to keep an open mind. What we think today may change tomorrow and what is OK. It is part of the learning process. As our awareness of the virus continues to grow, we are one step closer to persevering through this pandemic together.