COVID-19 is associated with a variety of potentially serious complications. These can include, but aren’t limited to, respiratory distress, blood clots, and acute kidney injury.

Another possible complication is multisystem inflammatory syndrome (MIS). This is when multiple areas of your body become inflamed after you have COVID-19.

While MIS is most often associated with children, it can impact adults as well. Continue reading as we explore what we know so far about MIS in adults.

MIS is a condition that’s associated with COVID-19. In MIS, inflammation affects multiple parts of your body, which can include your:

  • heart
  • brain
  • kidneys
  • liver
  • digestive tract
  • lungs
  • skin
  • eyes

MIS can happen in both adults and children. According to the Centers for Disease Control and Prevention (CDC), MIS in adults (MIS-A) is when the condition affects someone age 21 or older.

Like MIS in children (MIS-C), MIS-A is associated with COVID-19. It comes on in the time shortly after you’ve had COVID-19. Generally speaking, people typically develop MIS-A about 4 to 6 weeks after having COVID-19.

We’ve known that COVID-19 can cause high levels of inflammation in your body during severe illness. This is often accompanied by respiratory distress.

MIS-A is different in that it doesn’t always happen with respiratory symptoms. Instead, organ systems outside of your lungs are predominantly affected.

According to the CDC, people with MIS-A have a fever as well as more than one of the following additional symptoms:

Severe heart-related illness is also part of the main clinical criteria of MIS-A. As such, people with MIS-A can also have myocarditis, pericarditis, or dangerous arrhythmias.

It’s also possible for MIS-A to happen with neurological signs and symptoms such as neuropathy, seizures, and meningitis-like illness.

A low platelet count, which can lead to easy bleeding and bruising, can also occur.

MIS-A can become very serious. As such, if you develop symptoms of MIS-A, go to the emergency room or call 911 or local emergency services.

We still don’t know what exactly causes MIS-A. It appears as if the condition develops due to a dysfunctional immune response in the time after having COVID-19.

It’s also unclear why some people develop MIS-A and others don’t. It’s possible that differences in the immune system and genetics between individuals may play a role.

A 2021 study compared five people who had had MIS-A with healthy people. Laboratory studies found that the immune cells of people who had had MIS-A had a lower antiviral response to SARS-CoV-2, the virus that causes COVID-19, than those of healthy people.

DNA sequencing revealed a total of 12 different variations in genes associated with the immune and antiviral response in people with MIS-A. The researchers theorize that these may contribute to MIS-A, although they note that much more research is needed to support this idea.

In order to be diagnosed with MIS-A, a person must:

  • be age 21 or older
  • have been hospitalized for 24 hours or longer
  • not have another more likely cause of their symptoms
  • meet the current clinical criteria for MIS-A

Diagnosing MIS-A will start with a medical history and physical exam. While collecting your medical history, a doctor will ask about your symptoms, any other medical conditions, and if you’ve recently had COVID-19.

As a part of the physical exam, your vital signs will be taken. This includes measuring your blood pressure, heart rate, and body temperature.

If MIS-A is suspected, the following tests may be ordered:

There’s no standard way to treat MIS-A. It’s possible that you’ll be given treatments that help lower inflammation in your body. These may include corticosteroids or intravenous immunoglobulin (IVIG).

You’ll also receive supportive care. This includes things such as:

Since MIS-A is associated with COVID-19, taking steps to prevent developing COVID-19 is the best way to prevent it. This includes:

  • staying up to date on your COVID-19 vaccines and boosters
  • washing your hands frequently with soap and water
  • avoiding contact with those who have suspected or confirmed COVID-19
  • moving indoor activities outside, if possible
  • improving ventilation in indoor spaces, such as by opening windows and by changing air filters regularly
  • wearing masks and practicing physical distancing while out in public, as needed

According to the CDC, it’s still unclear why some adults develop MIS-A and others don’t. Identifying specific things that put an adult at risk of MIS-A is an area of ongoing research.

A 2021 review looked into the demographic features of 221 people who had had MIS-A. Within this group, it was found that people with MIS-A were more likely to be:

  • younger
  • male
  • Black or Hispanic

The researchers say that the reasons for the higher occurrence in these groups is unclear. They do note that the increased occurrence in Black and Hispanic people may be due to socioeconomic factors and inequalities in healthcare access.

MIS-A is a serious condition that requires treatment in a hospital. However, most people do recover from it.

A 2021 study included 15 people with MIS-A. While hospitalized, one-third of these individuals needed to be treated in the intensive care unit (ICU). However, none of the 15 people died.

The 2021 review mentioned earlier also explored the clinical characteristics of 211 people with MIS-A. The researchers noted that people with MIS-A were seriously ill, with more than half (57%) admitted to the ICU. A total of 15 individuals (7%) died.

Below, we’ll aim to briefly answer some of the additional questions that you may have about MIS-A.

How common is multisystem inflammatory syndrome in adults?

The exact incidence of MIS-A is unknown. Overall, it’s a rare condition, because most cases of COVID-19 are mild to moderate and can be treated at home.

MIS-A is also rather uncommon in those who are hospitalized with COVID-19. For example, one 2021 study found that out of 156 hospitalized people at risk of MIS-A, only 15 (9.6%) met the criteria for the condition.

Is multisystem inflammatory syndrome different in children?

MIS-A and MIS-C are generally similar. According to the CDC, outcomes for people with MIS-A may be more severe than for those with MIS-C. This is supported by data from the 2021 review that found that, compared with MIS-C, MIS-A was more likely to lead to:

  • a longer hospital stay
  • treatment with a ventilator
  • death

This finding could be due to the differences in the immune systems of adults and children as well as the higher likelihood of other underlying health conditions in adults.

Are there other conditions that are similar to multisystem inflammatory syndrome?

Yes. MIS has drawn comparisons to a condition called Kawasaki disease (KD). The exact cause of KD is unknown, but a viral or bacterial infection may contribute to it. Certain gene variations may also predispose a person to KD.

KD mainly impacts children and has symptoms such as fever, rash, and inflammation of the extremities, mouth, and throat. Like MIS, KD is also associated with heart-related complications.

MIS is a severe inflammatory condition that happens after COVID-19 and affects multiple parts of the body. While it’s more often reported in children, it can also happen in adults.

It’s unclear how exactly COVID-19 leads to MIS-A. It’s also not known why some people develop it and others don’t. This difference likely comes down to individual immune and genetic factors.

MIS-A is serious and needs to be treated in a hospital. If you have a history of recent COVID-19 and get symptoms such as rash, abdominal pain, and bloodshot eyes, get immediate medical care.