Strange gets stranger as Covid-19 now appears to invade more than the respiratory and digestive systems
Early analyses of Covid-19 patients in January told of the most common symptoms: fever, cough, and difficulty breathing. More diagnosed cases and research revealed less common symptoms, such as vomiting and diarrhea, indicating that in some people, the coronavirus was disrupting the digestive system, not just the respiratory tract.
By late February, we learned of mysterious cases involving no symptoms at all ? silent super-spreaders of a deadly disease who didn?t even know they had it and felt nothing. Then, last month, things got stranger, as reports emerged of diagnosed Covid-19 cases in people who had lost their sense of smell yet showed few or no other symptoms of the disease. Along the way, physicians reported some people with Covid-19 experiencing mild cold- or flu-like symptoms, ranging from sniffles to fatigue.
It?s not yet clear how SARS-CoV-2 might be affecting the brain, but experience with other viruses, including the flu, suggests it certainly could make its way there.
Evidence so far, however, involves only anecdotes from physicians telling of Covid-19 patients initially experiencing confusion, headaches, and other symptoms that may be caused by inflammation of the brain, along with early studies involving small numbers of patients ? sometimes just one.
Meanwhile, it?s not clear whether or to what extent the coronavirus attacks the brain directly versus Covid-19?s respiratory effects robbing the brain of oxygen.
?It is very difficult to separate the two,? says Chethan Rao, MD, a practicing physician and associate professor of neurology and neurosurgery at Baylor College of Medicine Medical Center.
Rao suspects both factors are at work. And things can deteriorate quickly. He has seen otherwise healthy Covid-19 patients go from talking normally while receiving a small amount of oxygen to being put on first a ventilator and then a more serious heart-lung support system, all in the space of four hours.
Multiple cases reported
The possibility that Covid-19 is invading the brain directly emerged back in February in a study out of Wuhan, China, the epicenter of the initial outbreak. Then, in March, researchers raised the possibility in the Journal of Medical Virology, stating that this coronavirus, SARS?CoV?2, is similar to others that ?are not always confined to the respiratory tract and? may also invade the central nervous system inducing neurological diseases.?
Recently, a woman in her late fifties who had experienced three days of cough, fever, and ?altered mental status? was tested for flu, which she did not have. Turns out she had Covid-19. Brain scans showed unusual swelling, and physicians diagnosed it as acute necrotizing hemorrhagic encephalopathy, which is ?a rare central nervous system complication secondary to influenza or other viral infections which is characterized by altered mental status and seizures, and often this further leads to profound disability or death.?
Other tests were done on the woman to eliminate some other viruses that might cause the diagnosed condition. (Influenza is known to cause, in some cases, encephalitis and its neurological consequences, such as strokes and seizures, Rao says.)
?This is the first reported case of Covid-19-associated acute necrotizing hemorrhagic encephalopathy,? the physicians, from the Henry Ford Health System in Detroit, concluded on March 31 in the journal Radiology. ?As the number of patients with Covid-19 increases worldwide, clinicians and radiologists should be watching for this presentation among patients presenting with Covid-19 and altered mental status.?
In another case, a 74-year-old man with preexisting neurological conditions had suddenly lost his ability to speak. He was ultimately diagnosed with Covid-19. ?Since Covid-19 affects the elderly more and those with preexisting conditions, patients with prior neurological conditions and acute respiratory symptoms are at an increased risk of encephalopathy on initial presentation,? his physicians wrote.
Getting into the brain
It?s not yet clear how SARS-CoV-2 might be affecting the brain, but experience with other viruses, including the flu, suggests it certainly could make its way there, Rao and others say.
SARS-CoV-2 is rather sneaky, a new study in the journal Nature suggests. The virus enters human cells through a certain type of cell receptor. It appears to often hold initially in the upper respiratory system, mainly in the throat, without typically causing many symptoms there.
Then, in cases destined to become more severe, the virus migrates into the lungs and/or the stomach.
The cells with the right receptors for SARS-CoV-2 are found extensively in the lungs, Rao tells Elemental, explaining why breathing problems are common in severe Covid-19 cases. But those receptors are also found in blood vessels in the blood-brain barrier and in nerve endings, he explains.
?It is definitely possible that the nervous system is being invaded through these means,? Rao says.
Until more definitive research can be done, Covid-19?s mysterious ways are an ever-moving target, says Peter Gulick, DO, an oncologist and infectious disease specialist at Michigan State University?s College of Osteopathic Medicine. And he?s not ready to accept the case studies as proof of what might be happening.
?Acute encephalitis is not a known presentation of Covid-19, even though it has presented with other coronaviruses,? Gulick says by email. ?But we will have to continue to follow cases to see if any neurological conditions do occur as a result of Covid-19.?