Many COVID-19 patients who have long-lasting symptoms report feeling weak or foggy after too much physical activity.
That's a hallmark of chronic fatigue syndrome, an often debilitating illness that can last several years or more.
Researchers are just beginning the understand the link between the coronavirus and chronic fatigue.
Further investigation into the similarities could be critical to patients' long-term care.
Before Marissa Oliver touched down in California in May, she was finally starting to feel recovered from COVID-19. Her breathing had improved: She could talk on the phone for half an hour or take a 40-minute walk without much discomfort. But traveling felled her almost instantly.
"I basically relapsed upon arrival," Oliver, a 36-year-old manager for an arts organization in New York City, told Business Insider.
Lately, she said, simple tasks like making back-to-back work calls can leave her "completely destroyed."
It's not uncommon for COVID-19 patients to endure a major setback in their recovery after too much physical activity. In fact, doctors say feeling weak or foggy after normal tasks has become a distinct pattern among patients with long-lasting symptoms. It reminds them of another condition that's also still somewhat mysterious: chronic fatigue syndrome.
Related: What coronavirus stress is doing to your brain and body
Patients with chronic fatigue — known clinically as myalgic encephalomyelitis — often "crash" or "relapse" from simple activities like taking a shower, going to the grocery store, or getting the mail. They may feel dizzy or weak from standing up too quickly, or struggle to think clearly. Some patients may become bed-ridden for several days or weeks, without feeling better after sleep or rest.
"There's talk in the the medical community about a chronic fatigue syndrome-like illness that could happen after coronavirus," Dr. Nate Favini, the medical lead at Forward, a primary-care practice that's collecting data on coronavirus patients around the country, told Business Insider. "Unfortunately, there will be a small subset of people for whom that becomes the case and these symptoms really do become a chronic thing that you're dealing with for years."
But COVID-19 patients need to be sick for at least six months in order to be diagnosed with chronic fatigue, and many haven't hit that mark yet. Even if they do eventually receive that diagnosis, though, no cure or approved treatment awaits them. Doctors are still working to understand chronic fatigue, which is often unpredictable and can bear a striking resemble to other illnesses like fibromyalgia.
Still, the pandemic has brought renewed attention to chronic fatigue. That could mean better treatments in the future for the newly diagnosed — and for those who've battled ' fatigue for years.
Chronic fatigue: poorly explained and poorly treated
There is no test to confirm that someone has chronic fatigue syndrome.
"It's very poorly explained and it's poorly treated," Dr. Frances Williams, a rheumatologist and professor of genomic epidemiology at King's College London, told Business Insider. She added: "The medical community is still not terribly accepting of the existence of such a thing."
The Centers for Disease Control and Prevention estimates that up to 2.5 million Americans suffer from chronic fatigue syndrome, the majority undiagnosed. The condition costs the US economy up to $24 billion a year in medical bills and lost incomes, according to the agency. Data suggests white people are more likely to receive a chronic fatigue diagnosis than other races.
Doctors aren't quite sure what causes chronic fatigue, but the syndrome can be triggered by infectious diseases like Lyme disease or Epstein-Barr virus. Some patients can be sick for several years, while others never fully regain their health. Some may never be able to return to work at all.
Though researchers are just beginning to study the relationship between chronic fatigue and the new coronavirus, they have some past clues from SARS patients who were infected in 2003.
A follow-up study of SARS patients in Hong Kong found that 27% met the CDC's clinical criteria for chronic fatigue syndrome four years after their illness began. Another study of 109 SARS patients in Toronto found that more than half the patients hadn't returned to work due to persistent fatigue and weakness a year after they were discharged from the ICU.
Some doctors suspect that COVID-19 patients may wind up out of work for long periods as well.
"One can anticipate — and this is a prediction — that a significant proportion of the population who were employed when they became ill with [COVID-19] may not be able to return to work in any meaningful way," Dr. Harvey Moldofsky, a professor emeritus at the University of Toronto who studied SARS patients, told Business Insider. "Can you imagine the economic impact?"
A link between the coronavirus and chronic fatigue
Based on what doctors know so far, blood clots may be one reason some COVID-19 patients feel fatigued.
"If people have a bunch of small clots in their lungs, that can continue to cause fatigue for a long period of time — even after the clots are gone — if there's damage to the blood vessels," Favini said.
An aggressive immune response to the virus could also trigger inflammation in the body that damages healthy tissue.
"We think that people's baseline immune system predicts who will get chronic fatigue," Dr. Frances Williams, a rheumatologist and professor of genomic epidemiology at King's College London, told Business Insider. Her research team is currently examining the link between the coronavirus and chronic fatigue syndrome among adult twins.
Williams pointed to a 2018 study that showed how inflammatory molecules can predict chronic fatigue syndrome in hepatitis C patients.
"The ones that had the biggest reaction to it and made more inflammatory cytokines were the people most likely to get chronic fatigue," she added. "It seems highly likely that that is what we will find in COVID, but we don't know the answer yet."
An overactive inflammatory response could impair the nervous system, resulting in depleted energy, muscle weakness, or trouble concentrating or sleeping. Moldofsky's 2011 study of SARS patients in Toronto found evidence that the virus had crossed the patients' blood-brain barriers, leading to long-lasting neurological problems that disrupted their sleep and cognition. The new coronavirus could operate in a similar manner.
"It's an inflammatory disease that is interfering with the conduction of the normal pathways of the nervous system," Moldofsky said.
Dr. Noah Greenspan, a physical therapist in New York City who works with long-haul coronavirus patients, said he's seen many patients for whom the simple act of sitting up or walking across a room makes their heart race or blood pressure drop. That's likely because the coronavirus is disrupting their autonomic nervous system, he said, which regulates blood pressure, heart rate, and body temperature.
"You're only going to heal as quickly as your slowest system, and unfortunately the neurologic system is one of the slower systems to heal," Greenspan said. "Until that inflammation goes away, you may not see the change."
Understanding how to treat post-COVID cases
Oliver said she's found ways to make her dizziness, headaches, and fatigue more manageable lately. Daily breathing exercises seem to help, as does taking a break whenever work gets stressful. She also tries to limit her social media activity to less than five minutes per day.
"I only get this fatigue — which they're saying is part of the post-COVID syndrome — if I overextend myself, like if I'm walking too much or talking too much," she said.
Doctors say taking it easy will be key in the recovery process for COVID-19 patients with symptoms of chronic fatigue.
"You have to go extremely slow with COVID patients because sometimes they can feel perfectly fine during a treatment or they can feel perfectly fine during an activity, but if you go that one step over the edge, then they could be knocked out for a week after that or they can have a flare in their symptoms," Greenspan said.
Sill, many patients find it difficult to know when they've reached their limit.
"There is no easy way of telling somebody or predicting what their exercise tolerance is," Williams said. "The best thing really is to listen to your body. If you know that something's pushed you over the edge in the past, then don't repeat it. Do something active, but for less time or less strenuously."
The more doctors understand chronic fatigue, she added, the more they'll be able to find ways to treat patients.
A few new investigations are already underway: In May, a coalition of scientists at the Open Medicine Foundation started a multi-year study to see whether COVID-19 triggered chronic fatigue syndrome. Rep. Jamie Raskin, a Democrat from Maryland, has also co-sponsored a bill in Congress that calls for $15 million in annual funding through 2024 to support research into COVID-related cases of chronic fatigue.
Having a proper diagnosis would also help COVID-19 patients with long-term fatigue get better care.
"Rheumatologists on the whole aren't interested in dealing with things that aren't inflammatory, and we're assuming that this will be a sort of post-inflammatory condition," Williams said. "It behooves us to work out where and who should be helping these people."
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