But the neurological symptoms now being seen in people who had milder cases of Covid-19 are more mysterious. Even the loss of smell that’s been a high-profile symptom of Covid-19 is considered neurologic, likely caused by dysfunction of olfactory nerves or nerve support cells, Koralnik said.
It’s possible, for instance, that small amounts of the virus still remain in outer reaches of the body, hiding out and continuing to wreak havoc. There’s precedent for continuing symptoms with other viruses, including the coronaviruses SARS and Middle East Respiratory Syndrome. Lingering virus has also been posed as an explanation in those settings.
So far, though, there’s not strong evidence that Covid-19 infects the brain.
A more likely scenario is that the body’s immune system continues to fire, even after the virus has been dispatched, according to Dipa Jayaseelan, a consulting neurologist at University College London Hospitals, who has studied neurological complications of Covid-19. In that case, she said, numerous antibodies and immune cells activated by the virus could go awry in subtle ways.
‘Into Overdrive’
“It isn’t the virus itself, but it’s the body’s reaction to the virus,” Jayaseelan said. “The body goes into overdrive” in fighting Covid-19 and may continue to overreact even after the virus is upended.
Allison Navis, a specialist in neuro-infectious diseases at the Icahn School of Medicine at Mount Sinai in New York, has seen about 50 long-haulers in the last month. She believes there isn’t one common cause, but rather a variety of different explanations. “It’s a big mystery,” she said. “Everyone’s commenting that they’re starting to see this.”
An immune reaction may have caused Musser’s dizziness and vertigo.
After a video consultation this month, Northwestern’s Koralnik diagnosed him with Covid-related inflammation of his inner ear nerves and prescribed a motion sickness drug along with specialized physical therapy. It was “truly relieving” to find out that he had something treatable, Musser said in an email.
Covid-19 patients who continue to grapple with symptoms aren’t alone. Some survivors of SARS and Middle East Respiratory Syndrome reported symptoms like fatigue and depression for years afterward.
Ebola, Zika
Ebola survivors often suffer from everything from headaches to joint pain to eye problems long after they recovered from the disease, studies have found. And Zika virus outbreaks have been linked to an higher incidence of Guillain-Barre syndrome, a rare autoimmune disorder where antibodies attack the nerves, sometimes leading to paralysis.
And while long-term brain and lung damage are key concerns with Covid-19, there is also a growing realization that the virus may cause subtle damage to other organs, including heart inflammation.
Tracking the cause of the neurological issues could take a while, given the difficulty of linking far-ranging immune effects to the virus. During the AIDS epidemic, a surge of patients coming in with dementia kick-started the field’s focus on infectious disease. But it took years after HIV was discovered for the concept of HIV-related dementia to become firmly established in the medical community.
At the National Institute of Neurological Disorders and Stroke, neurologist Avindra Nath said he’s received about 200 emails from patients reporting long-lasting neurological complications, including “brain fog,” burning sensations in the hands and feet, headaches and sleeping problems.