Shortly after the pandemic erupted last year, doctors were baffled by a wave of patients, mostly teenagers and young adults, who came in to complain about frostbite – painful lesions on their toes, and sometimes also on the fingers.
The condition has come to be called the Covid Toes. They were considered, like the loss of smell and taste, to be another strange telltale sign of the disease, even though most of the patients tested negative for the coronavirus. Doctors struggled to explain the association.
Lesions are red or purple in whites and often purplish or brownish in people of color. They cause painful burning or itching sensations and sometimes make it difficult to wear shoes or walk.
Now a new study from France, published in the British Journal of Dermatology, sheds light on the causes of Covid toes. Research indicates that lesions may be a side effect of the immune system’s shift to overdrive in response to exposure to the virus, which can damage cells and tissues in the process.
French researchers analyzed blood samples and skin biopsies from 50 patients who presented with frostbite-like lesions for the first time in April 2020, and who were referred to Saint-Louis Hospital in Paris. Just over half of the patients had other symptoms suggestive of Covid-19, such as cough, shortness of breath and loss of smell, but all tested negative for the virus on PCR tests.
The samples showed high levels of type 1 interferon, a protein that activates the body’s immune system to fight viruses, but which can also cause damage. Researchers have also found high levels of antibodies that can inadvertently attack the body’s own cells.
Abnormal changes in the walls of blood vessels may also play a role in the lesions, the study suggests.
While the relationship between coronavirus infection and frostbite-like lesions “is still controversial,” the authors wrote, “spikes in frostbite-like lesions concomitant with peaks in Covid-19 deaths in 2020 suggest strongly that this disorder is closely related to infection with SARS-CoV-2. . “
The explanation for Covid’s toes isn’t all that surprising; one of the hallmarks of the disease is an overreaction of the immune system called a cytokine storm, which can ultimately cause more illness than the virus itself.
German scientists published an article last year saying they had found a strong localized response induced by interferon in three young men who entered with frostbite. This article suggested that men, who tested negative for the coronavirus, may have developed frostbite several weeks after an initial infection caused mild or asymptomatic illness, and that the interferon-induced immune response may have led to early control of the virus and prevented respiratory tract disease.
Dermatologists say people with Covid toes generally do well and are unlikely to develop severe Covid, and the symptoms reflect a healthy immune response to the virus.
The new study suggested that treating Covid toes with local or systemic anti-inflammatory agents may be effective.