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Rapid pesawat: is the "corona toe" caused by the new coronavirus?

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Rapid pesawat: is the "corona toe" caused by the new coronavirus?

Original author | Cassandra Willyard

Although new research still shows that the new coronavirus does not cause inflamed toes and chilblains in infected people, the debate continues.

In March 2020, when COVID-19 cases in Boston, Massachusetts were just starting to climb, Esther Freeman noticed a lot of patients coming in with discolored toes. Freeman, director of global health dermatology at Massachusetts General Hospital, has seen these toes before. These itchy reddish-purple bumps are typical of chilblains - a skin condition common in winter. But in normal times, there are only one or two patients every winter. "Suddenly, there are now 15, 20 of these patients a day," she said. Physicians all over the world are taking notice, and it's interesting that the surge in patient numbers seems oddly aligned with the development of the new crown epidemic.

The media dubbed it the "corona toe," and when doctors tested these patients further, most of them never tested positive for the virus. This puzzled scientists and decided to find out.

Researchers are divided on whether the "corona toe" is caused by the new coronavirus infection. | Cordelia Molloy/Science Photo Library

The latest study [1], published on February 25, took an immunological perspective and analyzed 21 people who developedapa itu swab test antigen for sale - UDXBIO frostbite during the first months of the pandemic in Connecticut. Although the findings did not rule out a direct link between Covid-19 infection and frostbite, for 19 of them, the authors could not find immunological evidence that they had been infected with Covid-19. This result supports the view of some researchers that the "corona toe" is caused by something unrelated to the new coronavirus. For example, it may be because these people are not wearing shoes and socks at home during the lockdown, said study lead author Jeff Gehlhausen, a dermatologist and immunologist at Yale University School of Medicine.

Still, the findings raise "some very interesting questions that warrant further study," said Freeman, who was not involved in the study. For example, this study does not rule out the possibility that people exposed to the new coronavirus may be fighting the virus by means of an innate immune response - the innate immune response is the body's first line of defense and does not mobilize the body to respond to the new coronavirus. Detectable antibodies and T cells. So the whole mystery is still unsolved, she said.

Toes have something to say

The cause of frostbite has not been fully elucidated. "We think of chilblains as a cold-climate-related injury," said Patrick McCleskey, a dermatologist and researcher at Kaiser Permanente in California. "We always see some chilblains in the winter and then go away in the summer." It is thought that the cold may restrict blood flow, causing some cells to die, triggering an inflammatory mechanism. These red-purple bumps on the toes (and possibly fingers, ears, or nose) can be itchy, tingling, and sometimes extremely painful.

In this latest study, most of the subjects' "corona toes" appeared in April and May 2020, which coincided with a surge in cases in Connecticut. In the study, about 1/3 of the people said they had some symptoms of new crown infection before the "new crown toe" appeared, and 1/3 of the people said that they had been in contact with a confirmed or suspected infection of the new crown.

The research team used a variety of methods to look for antibodies and T cells specific for SARS-CoV-2 -- the body's signal for an adaptive immune response to the pathogen. It's been months since these people developed chilblains, and if they do have the virus, their immune systems should have had enough time to respond. But the research team only found signs of infection in two people, one of whom had been diagnosed positive for the new crown.

Many teams are looking for SARS-CoV-2 antibodies in chilblain patients, but "no one has really tested the T-cell response hypothesis," Freeman said. "This team has done an amazing job." But she also noted that the scale of the entire study Smaller, so the extrapolation is not strong, and larger-scale epidemiological studies [2,3] have found a correlation between frostbite and the new coronavirus.

Thierry Passeron, a dermatologist at the University of the Côte d'Azur in France, still believes that the new crown toe comes from the new crown virus. His team [4] found evidence in patients with frostbite during the epidemic that they developed a strong innate immune response. The team speculates that many of the people who suffered from frostbite during the outbreak cleared the virus this way, so almost none of these people produced antibodies, he said.

Puzzle Unsolved

The link between Covid-19 and frostbite is still inconclusive, and some researchers are starting to consider the possibility of a lockdown theory, that when the pandemic first emerged, many people spent more time barefoot at home, leading to cold sores on their toes. It's also possible that seeing a large number of reports of the new crown toe has made more people with symptoms decide to seek medical treatment.

For Freeman, "the whole problem hasn't come to the fore." On the one hand, she's seen people who, unsurprisingly, develop frostbite from walking in flip-flops in a snowstorm. On the other hand, she has also seen chilblains with no other apparent cause in coronavirus-positive patients.

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

Another possibility is that this phenomenon is decreasing. "There are still new cases of chilblains, but the numbers seem to be back to where they were before," said Yale dermatologist William Damsky, one of the authors of the paper.

All in all, it's a scientific question worth exploring, but the answer shouldn't affect the way dermatologists treat patients, McCleskey said. Chilblains generally go away on their own within two to three weeks, regardless of whether the patient has been infected with COVID-19.

"Honestly, I think the frostbite thing can be put aside," he said.


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. et al. J. Cutan. Pathol. 48, 47–52 (2021).

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

Originally published in the News section of Nature on March 6, 2022 under the headline Are 'COVID toes' actually caused by the coronavirus?