Monkeypox Linked to Myocarditis in New Case Study—Here's What To Know

A man who tested positive for monkeypox developed inflammation of heart muscle but made full recovery.

Patient at doctor's office getting his heart checked
Patient at doctor's office getting his heart checked. PeopleImages/Getty

Fast Facts

  • A 31-year-old man developed myocarditis, or heart inflammation, about a week after coming down with monkeypox symptoms, a case study found. 
  • Myocarditis is not a common complication of monkeypox, experts said, and there have only been a handful of cases despite tens of thousands of monkeypox infections. 
  • The condition usually improves on its own or with medication, but people should seek medical attention if they have chest pain, abnormal heart rhythms, or other symptoms. 

Monkeypox has primarily been shown to cause blisters and a pimple-like rash but a recent case study published in JACC: CASE Reports indicates some patients may also experience damage or swelling to the heart.

The report, developed by researchers and doctors in Portugal, said a 31-year-old male patient with a confirmed monkeypox infection developed acute myocarditis—inflammation of the heart— about one week after the onset of virus symptoms.

"This case highlights cardiac involvement as a potential complication associated with monkeypox infection," Ana Isabel Pinho, MD, department of cardiology at São João University Hospital Centre in Portugal and lead author of the study said in the American College of Cardiology press release.

Reporting this "potential causal relationship," can raise awareness in the scientific and health care communities that acute myocarditis may be a possible complication connected with monkeypox, Pinho added. And having this additional information may be helpful to recognize other complications associated with monkeypox in the future.

Monkeypox Patient Impacted by Myocarditis

The first case of monkeypox causing heart damage began when a 31-year-old male patient went to a health clinic five days after experiencing monkeypox symptoms such as fever, myalgia, malaise and also skin lesions on his face, hands and genitalia.

The patient took a PCR test to confirm the monkeypox diagnosis and went home. He returned to the emergency room three days later however, experiencing chest pain and tightness that spread to his upper left arm, according to the case report.

Doctors admitted the patient to intensive care and conducted a variety of tests to check for heart problems. After using an electrocardiogram (ECG) – a simple test to check the heart's rhythm and electrical activity – and conducting bloodwork and other lab tests, abnormalities were discovered including elevated levels of C-reactive protein, creatine phosphokinase (CPK), high-sensitivity troponin I and brain natriuretic peptide (BNP), which are indications of stress injury to the heart.

A cardiac magnetic resonance (CMR) study was also performed on the patient. Since the results were "consistent with myocardial inflammation," the patient was diagnosed with acute myocarditis.

After one week in the hospital, the patient fully recovered and was discharged.

How Common Is It For Monkeypox to Trigger Heart Complications?

While the recent case study identified one individual with a confirmed diagnosis of monkeypox who developed acute myocarditis, health experts say inflammation of the heart is unusual and is likely a rare complication linked with monkeypox.

"This is uncommon. There has been more than one case by now, but most people with monkeypox do not develop myocarditis," Jorge Salinas, MD, assistant professor of medicine and infectious diseases at Stanford University, told Health.

A report published in the New England Journal of Medicine found that of 528 patients diagnosed with monkeypox between April and June 2022, only two cases of myocarditis were reported among them. Both cases were resolved within a week.

"In the United States, there have already been 20,000 cases of monkeypox and there may have been a handful of cases of myocarditis by now," Dr. Salinas said. "But again, it's a handful out of 20,000, and of those, only a handful, in other words, a small percentage of those people are likely to have myocarditis or severe myocarditis."

The heart can be inflamed in several different ways, but it is most commonly caused by an infection that occurs in the body, according to Dr. Salinas. These infections typically come from viruses, including the common cold, flu, COVID-19, bacteria, fungus and parasites.

"Myocarditis is not that common, but among the cases of myocarditis, a very common cause is viruses," he said.

A research study from 2018 found that viral infections are the most common cause of myocarditis. Other causes include bacterial infections, toxins, autoimmune diseases and drug reactions.

In addition, other viruses such as smallpox have been closely associated with myocarditis and cardiovascular problems. Because monkeypox is part of the same family of viruses that causes smallpox, experts say that it may cause cardiac inflammation in certain circumstances.

"Monkeypox is closely related to smallpox, which has a known predilection for causing cardiac inflammation. Similar to smallpox, cardiac involvement is uncommon but can and does occur," Sharon Nachman, MD, Chief of the Division of Pediatric Infectious Diseases at Stony Brook Children's Hospital, told Health.

Signs and Symptoms of Myocarditis To Watch For

At this time, it's not clear who goes on to develop myocarditis after a confirmed monkeypox diagnosis, Dr. Salinas said. However, there are some signs and symptoms you can look out for if you have monkeypox and may be concerned about heart complications or issues.

  • Chest pain
  • Rapid or abnormal heart rhythms and rate
  • Palpitations
  • Difficulty breathing or shortness of breath (both at rest or during physical activity)
  • Feeling short-winded
  • Swelling in the legs, ankles or feet
  • Body aches or joint pain
  • Fatigue

If you notice any of these symptoms, you should seek care from your health care provider or a medical professional and visit an emergency room, Dr. Salinas and Dr. Nachman said. Patients should also report a monkeypox exposure or current symptoms to their provider.

"Any person that develops monkeypox and has chest pain or any other related symptoms should be seen and should seek care," Dr. Salinas explained. "But, I don't think that people need to be worried. Myocarditis is going to be unlikely and severe myocarditis is probably going to be even less likely."

If you are diagnosed with monkeypox and have a history of heart disease, severe immunosuppression, or an HIV infection it's also a good idea to speak with a medical provider regarding care.

"Anyone that is immune suppressed or that has a history of heart disease, could talk to their primary care doctor if they get diagnosed with monkeypox," Dr. Salinas said. "More importantly, those people that are at risk of severe diseases are eligible for treatment with a medication called TPOXX and perhaps taking the antiviral could help prevent going into these more severe manifestations."

Prognosis for Monkeypox Patients Who Develop Myocarditis

In the rare case that myocarditis occurs, it usually improves on its own or with the use of medication.

"Myocarditis has a spectrum and most cases will be mild or moderate," Dr. Salinas said. "In other cases, anti-inflammatory medications can be given and then it gets better."

If a patient develops chronic or severe myocarditis either because of genetic predisposition or how aggressive the viral infection is, patients may need further treatments, interventions, surgery or hospitalizations, Dr. Salinas and West added. In such cases, damage suffered by the heart may not recover completely.

"In some cases, if the inflammation is really bad it can affect and potentially kill a large number of heart cells," Dr. Salinas explained. "Because the heart may or may not function the same way as before, the person may need to go into the intensive care unit, be mechanically ventilated, or even be considered for a heart transplantation."

At this time, it is difficult to predict or know how often infected individuals with monkeypox will progress to have cardiac inflammation, Dr. Nachman said. It is also not known how long the cardiac involvement will last or if there will be long-standing damage after the virus has left the body.

"We don't know how often it will happen, but are cautious in expecting that it can happen," she said. "With early treatment, we are hopeful that progression to involve the heart will be less likely to occur."

While the case study provides more information about potential complications associated with monkeypox, this development should not change the way people view the virus or how it is treated when contracted.

"The medical community needs to know of these less frequent manifestations of the infection, but I don't think that the public needs to modify how they perceive monkeypox as a result of this report," Dr. Salinas said. "Monkeypox is still a disease that should be avoided. If you're at risk of getting monkeypox, you should get vaccinated, regardless of this case of myocarditis."

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