COVID toe: What does it tell you?

New research suggests that COVID toe – a form of COVID-19–associated pernio or chilblains – may be a side effect of the immune system's response to fighting off the virus.

Chilblains are cold-induced dermatosis, characterized by erythema and swelling at acral sites such as the toes and fingers. The lesions are often painless but can be sore and itchy, red, or purple. Most people develop the lesion only on their toe, hence the term COVID toe.

2 factors at play

Skin and blood tests performed on COVID-19 patients hinted that two factors may be at play in the development of the COVID toe. The first is the antiviral protein called type 1 interferon, while the second is an antibody that mistakenly attacks the person’s own cells and tissues, other than the invading virus.

Additionally, the cells lining the small blood vessels and supplying the affected areas have a role to play, said researchers from France.

“Our findings support an activation loop in the skin in chilblain lesions associated with endothelial alteration and immune infiltration of cytotoxic and type I IFN-polarized cells, leading to clinical manifestations,” they reported.

The research included 50 individuals with suspected COVID toe and 13 others with similar chilblain lesions which appeared prior to the pandemic, suggesting that the lesions were not related to COVID-19 infection.  

Rarer after Delta, COVID jabs

According to Dr Veronique Bataille, a consultant dermatologist and spokeswoman for the UK-registered charity British Skin Foundation who is unaffiliated with the study, COVID toe was frequently reported during the early phase of the pandemic but were less common following the emergence of the Delta variant.

“Presentations after vaccination are also much rarer,” she added. “This could be because more people are getting their COVID-19 shots, or due to better protection against recurrent disease as a result of previous infections.”

Novelty after another

Even in Italy, an epidemic of acute and self-healing vasculitic lesions of the hands and feet not previously observed with COVID patients was reported among asymptomatic children and adolescents in May 2020. “These lesions constituted a novelty that led us to establish a link with a more severe novelty – COVID-19, and both occurred almost simultaneously,” the researchers said.

“Although the epidemiology and clinical features of chilblain-like lesions have been extensively studied and published, little is known about the pathophysiology involved,” said senior investigator Dr Charles Cassius from the University of Paris, France. “Our current findings provide new insights and a deeper understanding of chilblain-like lesions.”

Meanwhile, Dr Amy Paller, paediatric dermatologist and chair of Dermatology at Northwestern Feinberg School of Medicine, said children and teenagers are usually the ones who develop COVID toes. “Many never develop the more common symptoms of COVID-19 such as a dry cough, fever, and muscle aches. And when they do have symptoms, they tend to be mild.”

While COVID toes go away without treatment, some people could have it for weeks or months. She said hydrocortisone cream may be applied to the affected area to reduce pain or itching. But if this fails, or symptoms worsen, referral to a dermatologist is recommended.