Are ‘COVID toes’ real, and what do they say about our immune system?

One symptom of coronavirus is located on an unexpected body-part – toes. Chilblain-like lesions (CLL), or red swellings on toes and fingers, have been associated with COVID-19 since December of last year, and while there was a clear link between the disease and the symptom, the reason behind the painful and sometimes weeks-long phenomenon remained unknown.

A research team in France set out to find the answer. The team observed 50 patients with and without COVID, with and without Chilblain-like lesions. They found that while regular Chilblain spots and coronavirus lookalikes had some overlapping qualities, the basic mechanism behind the two appears to be different.

As the farthest extremities in our blood system, fingers and toes can hold clues regarding our circulation. They turn blue in cold temperatures, indicating that the body is working on keeping the heat inside vital organs by minimizing circulation to the periphery.

Seasonal Chilblain lesions are common and occur with exposure to cold weather. The cause is believed to be the shrinking and dilating blood vessels causing a bottleneck effect that makes fluid leak into the tissue and leads to swelling.

The new study, which was recently published in the British Journal of Dermatology, found that while common chilblain lesions and COVID CLL lesions both expressed a level of inflammation, the coronavirus lesions also showed deposits of IgA antibodies – proteins that the body creates to attack invading particles – as well as high levels of type I interferon cytokines that urge the body to attack an invader. 

Interestingly, the type of antibody found – IgA – is seen in many auto-immune diseases where the body mistakenly attacks its own cells, thinking they are external. Examples of these diseases include Celiac, Lupus and IgA vasculitis.

In addition, the study found that the lining of the blood vessels, or endothelium, suffered changes and allowed for greater infiltration of immunological components, thus explaining the swelling and inflammation. 

This means the cause of the blistering toes in COVID isn't the collapsing and dilating tubes like in seasonal Chilbain, but a deeper change in the lining itself in response to the body's efforts to fight the virus.

"The epidemiology and clinical features of chilblain-like lesions have been extensively studied and published, however, little are known about the pathophysiology involved," said Dr. Charles Cassius, one of the authors of the paper.

"Our findings support an activation loop in the skin... that causes the clinical manifestation." The paper concludes.