A strong immune response to the SARS-CoV2 coronavirus is likely the cause of “Covid toes,” according to a new study. The unusual symptom was first reported early on in the pandemic in people who typically had mild disease, with people reporting burning or itching in their toes, along with redness and sometimes lesions on the toes, similar to chilblains, but without exposure to the cold.
The new study published in the British Journal of Dermatology looked at both skin and blood samples from 50 patients who reported Covid toes symptoms in April 2020 and who had never had chilblains before. In the blood, the researchers found high levels of two proteins that control a strong immune response, but can also cause damage to healthy tissues in the process. One of these, type I interferon is produced in response to viral infection and has important roles in orchestrating an immune response to the virus. Many of the patients also had detectable “auto-antibodies” which negatively react with a person’s own cells and tissues.
The scientists also found biological markers which indicated changes in blood vessels, a high density of which are found in the toes. The study provided more evidence that rather than being caused directly by the virus itself, Covid-toes are associated with a robust immune response to the virus.
“I explain it to my patients as follows: “your body had a strong (and generally good!) immune response to the virus, which caused your body to make Type I Interferon. We can think of your toes as a sort of innocent bystander, that turned red/purple because of this immune response,” said Esther Freeman, MD, PhD, Director of Global Health Dermatology at Massachusetts General Hospital and Associate Professor at Harvard Medical School.
Covid-toes are generally treated with steroid creams applied directly to the toes and often go away on their own, but some patients do develop long symptoms which can last up to a year.
“Patients with long lasting changes to the skin and pain in the toes can be harder to treat, so I think this new paper will help us think through more treatment options and understanding more of the pathophysiology of Covid-19 will help us to develop further targeted therapies for this condition,” said Freeman who is also Principal Investigator of the Covid-19 Dermatology Registry and was not involved in the new study.
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The researchers did tests on samples from patients collected in April 2020 who were likely infected with the original SARS-CoV2 variant. Now other variants including Delta are prominent throughout the world, how does this affect the number of people experiencing Covid-toes or the severity of the symptom?
“We don’t know the answer to this question yet – though I think it’s an important one,” said Freeman. “What is really needed are large community based studies of symptoms to understand how Delta symptoms may be similar or different to prior SARS-CoV-2 strains,” Freeman added also noting that people are generally familiar with Covid-toes as a phenomenon now, hence may be less likely to seek medical help for it, making it more difficult to figure out whether anything is different with the Delta variant and Covid-toes.