Is the "new crown toe" caused by the new crown virus?

Original author | Cassandra Willyard

Although new research still shows that the new crown virus does not cause inflammation and frostbite on the toes of infected people, the debate continues.

In March 2020, as covid-19 cases began to climb in Boston, Massachusetts, Esther Freeman found that many patients with discoloration of their toes came to the hospital. Freeman, director of Global Hygiene Dermatology at massachusetts general hospitals, has seen this toe before. These itchy reddish-purple bumps are typical of frostbite, a skin disease commonly found in winter. But in the usual case, there are only one or two patients every winter. "All of a sudden, there are now 15 or 20 of these patients a day," she said. "Doctors around the world are taking notice of this phenomenon, and interestingly, the surge in patient numbers seems to be surprisingly consistent with the development of the COVID-19 pandemic.

The media called it a "COVID-19 toe," and when doctors further examined these patients, most of them had not tested positive for COVID-19. This puzzled the scientists and decided to find out.

Researchers have mixed opinions on whether the "new crown toes" are caused by the coronavirus infection. | Cordelia Molloy/Science Photo Library

The latest study, published Feb. 25[1], looked at immunologically and analyzed 21 people with frostbite in the first few months of the outbreak in Connecticut. Although the findings did not rule out a direct link between COVID-19 infection and frostbite, the authors could not find immunological evidence that they had been infected with COVID-19 for 19 of them. This result supports the view of some researchers that the "covid-19 toe" is caused by causes unrelated to the new crown virus. For example, it could be because these people didn't wear shoes and socks at home during the lockdown, said Jeff Gehlhausen, the study's lead author and a gesthologist and immunologist at Yale Medical School.

Still, the findings throw up "some very interesting questions that merit further study," said Freeman, who was not involved in the study. For example, the study did not rule out the possibility that people exposed to the new coronavirus may be fighting the virus in the same way as an innate immune response — the body's first line of defense and does not mobilize the body to produce detectable antibodies and T cells against the new crown virus. So the whole puzzle is still unsolved, she said.

The toes have something to say

The causes of frostbite have not been fully elucidated. "We think frostbite is a damage associated with cold climates." Patrick McCleskey, a researcher and dermatologist at Kaiser Permanente in California, said, "We always see some frostbite in the winter and then slowly disappear in the summer." The researchers believe that the cold may restrict blood flow, causing some cells to die, activating an inflammatory mechanism. These reddish-purple bumps on the toes (or maybe fingers, ears, or nose) can be itchy, tingling, and sometimes severe.

In the latest study, most of the subjects' "covid-19 toes" appeared in April and May 2020, when COVID-19 cases in Connecticut also happened to be surging. In the study, about one-third of the people said they had some symptoms of covid-19 infection before the "new crown toe", and one-third said that they had been exposed to confirmed or suspected new crown infection.

The research team used a variety of methods to look for antibodies and T cells specific to the new coronavirus — which are also signals for the body to produce an adaptive immune response to the pathogen. It's been months since these people develop frostbite, and if they do have covid-19, their immune systems should have had plenty of time to respond. But the team found signs of infection in only two people, one of whom had been diagnosed positive for COVID-19.

Many teams are looking for antibodies to covid-19 in frostbite patients, but "no one has actually tested the T-cell response hypothesis," Says Freeman, "and the team has done an amazing job." However, she also noted that the entire study was smaller, so extrapolation was not strong, while larger epidemiological studies [2,3] had found a correlation between frostbite and the new crown virus.

Thierry Passeron, a dermatologist at the University of the Côte d'Azur in France, still believes that the toes of the new crown originate from the new crown virus. His team[4] found evidence in patients with frostbite during the pandemic that they developed a strong innate immune response. The team speculates that many people with frostbite during the pandemic cleared the coronavirus in this way, so these people hardly produced antibodies, he said.

The puzzle is unsolved

Previous studies [5,6] have used tissue biopsies and stained samples to identify the components of the virus to test whether people with frostbite have been infected with the new crown virus. Gehlhausen and colleagues tried the stain and found that the stain would attach to some of their tissue samples. They also randomly tested the stain with samples of tissue from pre-pandemic tissues during the period before the coronavirus epidemic began, and found that the stain also marked these areas. Gehlhausen said: "Our study shows that this stain may lack specificity. ”

The relationship between COVID-19 infection and frostbite remains inconclusive, and some researchers are beginning to consider the possibility of lockdown theory that many people spend more time at home barefoot when the outbreak first appeared, causing frostbite to get cold on their toes. It may also be that seeing a lot of reports of COVID-19 toes has made more people with symptoms decide to seek medical attention.

For Freeman, "the whole problem hasn't come to light yet." On the one hand, she had seen people who had not unexpectedly developed frostbite because they were walking in flip-flops in a snowstorm. On the other hand, she has also seen patients who are positive for the new crown virus have frostbite for no other obvious reason.

The debate over the issue has also begun to polarize, Gehlhausen said. But the different theories are not incompatible. "It's also possible that all of these situations exist," he said, "and I don't support either side." ”

There is also the possibility that this phenomenon is decreasing. "There will still be new frostbite patients, but the number seems to be back to the previous level." William Damsky, one of the paper's authors and a gethologist at Yale, said.

All in all, it's a scientific question worth exploring, but the answer shouldn't affect the way dermatologists treat patients, McCleskey said. Whether the patient has been infected with COVID-19 or not, frostbite usually disappears on its own within two to three weeks.

He said, "Honestly, I think frostbite can be put aside. ”

bibliography

1. Gehlhausen, J. R. et al. Proc. Natl. Acad. Sci. USA 119, e2122090119 (2022).

2. Mascitti, H. et al. Eur. J. Clin. Microbiol. Infect. Dis. 40, 2243–2248 (2021).

3. Visconti, A. et al. Br. J. Dermatol. 184, 880–887 (2021).

4. Hubiche, T. et al. JAMA Dermatol. 157, 202–206 (2021).

5. Ko, C. J. and al. J. Cutan. Pathol. 48, 47–52 (2021).

6. Colmenero, I. et al. Br. J. Dermatol. 183, 729–737 (2020).

The original article was published in the news section of Nature on March 6, 2022 under the headline of Are 'COVID toes' actually caused by the coronavirus?

nature

Copyright Notice: