Coronavirus causes the body’s own immune system to attack itself, a new study of medical scans has confirmed.

The body’s immune system is responsible for the “long-term and bizarre” symptoms among severe Covid-19 patients, scientists say.

They said that most people who catch the virus suffer only mild symptoms such as muscle soreness and achy joints.

But for some patients, these symptoms are more severe – such as rheumatoid arthritis flares and autoimmune myositis, commonly referred to as Covid toes.

Due to the lack of research as the virus was so new, doctors have struggled to explain exactly what causes these long-term symptoms.

Now researchers at Northwestern University in the United States have used radiological images to identify the culprit – our own immune system.

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MRI image of a patient’s shoulder – the red arrow points to inflammation in the joint
(Image: Northwestern University SWNS)

Study author Dr Swati Deshmukh said: “We’ve realised that the Covid virus can trigger the body to attack itself in different ways, which may lead to rheumatological issues that require lifelong management.”

Data from patients who presented themselves to Northwestern Memorial Hospital between May 2020 and December 2020 was analysed by the researchers.

Some of the patients, who experienced long lasting symptoms, requiring medical treatment, received an MRI, CT scan or ultrasound.

Looking at these images, the researchers were able to determine the origin and nature of their symptoms.

Dr Deshmukh said: “Many patients with Covid-related musculoskeletal disorders recover, but for some individuals, their symptoms become serious, are deeply concerning to the patient or impact their quality of life, which leads them to seek medical attention and imaging.

“That imaging allows us to see if Covid-related muscle and joint pain, for example, are not just body aches similar to what we see from the flu, but something more insidious.”

The scans revealed inflammations, damaged nerves and blood clots, caused by the body’s immune system in response to the virus, the researchers found.

Dr Deshmukh said: “We might see swelling and inflammatory changes of the tissues, hematomas or gangrene.

“In some patients, the nerves are injured and in others, the problem is impaired blood flow.”

In some cases, doctors were unable to put their finger on what was wrong, because they did not know what to look for, the researchers say.

Dr Deshmukh said: “Some doctors request imaging for patients with Covid toes, for example, but there wasn’t any literature on imaging of foot and soft tissue complications of Covid.

“How do you find something if you’re unsure of what to look for? So in our paper, we discuss the various types of musculoskeletal abnormalities that radiologists should look for and provide imaging examples.”

Radiological imaging, like MRI or CT scans, could help doctors point patients in the right direction when it comes to treatment.

Dr Deshmukh added: “For example, if a patient has persistent shoulder pain that started after contracting Covid, their primary care provider might order an MRI or ultrasound.

“If a radiologist knows Covid can trigger inflammatory arthritis and imaging shows joint inflammation, then they can send a patient to a rheumatologist for evaluation.

“In some cases, radiologists may even suggest a Covid diagnosis based on musculoskeletal imaging in patients who previously didn’t know they contracted the virus.”

The findings were published in the journal Skeletal Radiology.

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