New research offers details about the mysterious 'COVID toes' symptom — but raises questions, too

• A new letter in the journal JAMA Dermatology asks dermatologists not to rule out the association between purple, swollen feet and coronavirus infections.
• The symptom, known as "COVID toes," has been identified among a number of coronavirus patients, but some studies suggest that the link is tenuous.

Dermatologists detected an usual symptom among coronavirus patients in April: purple, swollen toes that appeared frostbitten.

At the time, doctors weren't sure whether the condition — informally known as "COVID toes" — was an anomaly. But a growing number of coronavirus patients have displayed similar lesions over the last few months.

A Thursday editor's note in the journal JAMA Dermatology asked dermatologists to consider the link between the coronavirus and purple, swollen feet.

"Its close temporal appearance with the COVID-19 pandemic suggests that the two are associated," Dr. Claudia Hernandez, a dermatologist at Rush University Medical Center in Chicago, and Dr. Anna Bruckner, a dermatologist at the University of Colorado School of Medicine, wrote. "Dermatologists must be aware of the protean cutaneous findings that are possibly associated with COVID-19, even if our understanding of their origins remains incomplete."

When doctors began observing the symptom in April, it appeared to be more common among younger, relatively healthy patients who showed few or no other symptoms. But a few Chinese studies in March identified lesions and purple toes among patients with severe infections as well.

The lesions could be the product of general inflammation in the body or inflammation in the walls of the blood vessels — known as "vasculitis." They might also result from blood clots in skin vessels, or a combination of all three factors, Esther Freeman, a dermatologist at Massachusetts General Hospital, previously told Business Insider.

Dermatologists struggle to link 'COVID toes' to their namesake

Despite its name, "COVID toes" isn't considered an official COVID-19 symptom by the US Centers for Disease Control and Prevention. Much of what we know about the condition comes from a registry launched by The American Academy of Dermatology that tracks dermatological issues among coronavirus patients. Out of more than 200 submissions from healthcare providers in April, about half noted lesions on the hands or feet that resembled frostbite.

Spanish dermatologists also identified coronavirus infections in 29 out of 71 patients with purple, swollen toes in April. The doctors concluded that it was unlikely that something other than the coronavirus caused the symptom, given the timing and warm weather.

Other studies, however, have struggled to explain the phenomenon.

In a study published Thursday, doctors in Valencia, Spain, concluded that the coronavirus was not the cause of undiagnosed lesions among 20 hospitalized children in April. The patients didn't have any other coronavirus symptoms, and tested negative for both an active coronavirus infection and coronavirus antibodies.

Another study, also published Thursday, found no evidence of coronavirus infection among 31 patients with inflamed, purple lesions in Brussels, Belgium, in April. The authors suggested that the symptoms resulted from "lifestyle changes" during quarantine, including more time spent in sedentary positions.

But dermatologists in Madrid found that "COVID toes" may occur later in the course of a coronavirus patient's illness — when that patient may no longer test positive for an active infection. On average, patients in their study developed skin lesions around nine days after their first coronavirus symptoms arrived.

For now, the link between "COVID toes" and coronavirus infections remains tenuous, but dermatologists stress that the association cannot be ruled out.