What to Know About Eosinophilic Asthma

Updated: Mar. 11, 2022

Eosinophilic asthma is a rare but often severe type of asthma. Learn why experts say it can be dangerous—and how today's treatments offer a promising outlook for managing this chronic disease.

Is all asthma the same?

Asthma is a chronic respiratory disease that causes inflammation in the airways—the tiny tubes that carry air in and out of our lungs. When this inflammation is triggered, the airways tighten and narrow even more, often causing people to wheeze, experience chest tightness, and have difficulty breathing.

Of the 25 million Americans living with asthma, most experience symptoms due to a hypersensitivity to triggers such as allergies or exercise, or airway irritants such as smoke and pollution.

But in rare cases, asthma symptoms aren’t caused by these typical offenders. For some people, high levels of a certain type of white blood cell provoke their symptoms.

The condition is called eosinophilic asthma, and it’s a severe form of the disease.

What is severe asthma?

Asthma is what’s called a heterogeneous disease, says Kirsten Kloepfer, MD, an assistant professor at Indiana University School of Medicine who specializes in asthma and allergies. This means there are different subtypes of the disease that act differently in the body.

Over the last decade, Dr. Kloepfer explains, research has allowed doctors to group patients into specific subtypes based on sets of similar, observable characteristics.

Researchers aren’t sure what causes asthma, making it difficult to prevent or cure the disease. But today’s evolving classification system empowers better outcomes for people with asthma. It helps medical professionals better understand which subtypes best respond to which treatments.

Up to 10 percent of people with asthma have a severe variety, however, according to the American Lung Association (ALA). In these cases, people struggle to get their asthma symptoms under control despite treatment measures like medication, trigger avoidance, and adherence to an asthma action plan.

What is eosinophilic asthma?

Researchers are still trying to classify asthma types even further, Dr. Kloepfer says. The goal is to pave the way for more targeted, effective treatments for all forms of the disease.

One of these approaches is to classify asthma based on specific physiological biomarkers called eosinophils.

“Eosinophils are white blood cells that are part of the body’s protective immune system,” explains Marc Rothenberg, MD, PhD, director of the Cincinnati Center for Eosinophilic Disorders and director of allergy and immunology for the Cincinnati Children’s Hospital Medical Center.

Normally, these eosinophils make up a very small minority of our white blood cells, he says. But some people have higher levels in their blood and/or nasal septum.

What do eosinophils do?

Eosinophils are pro-inflammatory cells that play an important role in fighting off infections in the body. They’re typically activated by disease, but in people with eosinophilic asthma, stimuli like allergens, viruses, and pollutants can also trigger eosinophils to recruit.

But while these cells are powerful enough to kill things like parasites, Dr. Rothenberg says, they also have the capacity to damage a person’s own tissues—like lung epithelial cells.

In addition, eosinophils can stimulate a range of strong pro-inflammatory messengers such as leukotrienes, Dr. Rothenberg adds. These cells promote swelling that can narrow airways, increase mucus production, and attract other white blood cells.

This is why in excess, eosinophils contribute to asthma symptoms. Research published in Clinical and Experimental Allergy supports this connection, finding that higher levels of eosinophils in the body correlate with more severe asthma symptoms.

How common is eosinophilic asthma?

While studies show this subtype accounts for only about 5 percent of all asthma cases, it’s the most common form of severe asthma, according to a study published in Current Medical Research and Opinion.

The researchers found that up to 50 percent of people with severe asthma have high eosinophil counts—and when it’s uncontrolled, this subtype of asthma is associated with a higher risk of asthma attacks and worse lung function than non-eosinophilic asthmas.

Young Woman With Inhaler Having Asthma Attack, CloseupPixelsEffect/Getty Images

What are the symptoms of eosinophilic asthma?

Eosinophils’ inflammatory effect on the airways leads to symptoms similar to other forms of asthma, including shortness of breath, chest tightness, and coughing.

According to the American Partnership for Eosinophilic Disorders, however, people with eosinophilic asthma are more likely to experience additional symptoms.

This is because the excess of eosinophils can cause swelling throughout the whole respiratory system—not just the airways. This can provoke:

  • Chronic sinus infections and congestion
  • Nasal polyps
  • Inflamed nasal mucous membranes
  • Anosmia, or lost sense of smell

Who is at risk for eosinophilic asthma?

Doctors don’t know why some people have higher levels of eosinophils than others. But Dr. Kloepfer says eosinophilic asthma is much more common among people who develop asthma as an adult (late-onset or adult-onset asthma).

Factors like environmental exposures and family history may also contribute to its development, Dr. Rothenberg adds.

One potential sign of eosinophilic asthma is an inability to control asthma symptoms with standard treatments like inhaled corticosteroids. This suggests a case of severe asthma, which the ALA classifies into three types:

  • Severe allergic asthma
  • Eosinophilic asthma
  • Non-eosinophilic asthma

A doctor can then confirm an eosinophilic asthma diagnosis by testing a patient’s blood for eosinophil levels, Dr. Kloepfer says. Your doctor might also look for an excess of these white blood cells in an airway sample.

How is eosinophilic asthma treated?

Inhaled corticosteroids are the first line of treatment for many types of asthma. These medications work to keep inflammation at bay so airway tightening—and the resulting asthma symptoms—are less likely to occur.

Yet daily inhaler medications don’t always help people with severe asthma control their symptoms, Dr. Kloepfer says. While oral steroids such as prednisone deliver a stronger, more effective dose of the drug, they’re not usually recommended for long-term therapy. This is because frequent or daily use of oral steroids puts people at a greater risk for weight gain, diabetes, glaucoma, osteoporosis, and other negative health effects, she says.

Instead, there’s a newer approach to treating eosinophilic asthma: Injectable medications called biologics. These drugs work by blocking the pathways that encourage high levels of eosinophils, limiting their effects.

Dr. Kloepfer says there are currently three biologic therapies approved by the U.S. Food and Drug Association to treat moderate to severe eosinophilic asthma. These include:

  • mepolizumab (Nucala)
  • reslizumab (Cinqair)
  • benralizumab (Fasenra)

These types of drugs selectively target eosinophils, Dr. Rothenberg says.

Fasenra activates other immune cells to kill eosinophils directly. Nucala and Cinquair work by blocking eosinophils’ growth factor, a protein called interleukin-5 (IL-5.)

Why management is important

Any form of untreated asthma is dangerous. The Asthma and Allergy Foundation of America estimates that 10 Americans die of the chronic disease per day—and most of these fatalities are avoidable with proper medical treatment.

Uncontrolled eosinophilic asthma poses additional risks, however.

Long-term risks

Eosinophils can contribute to a phenomenon called airway remodeling, explains Ekta Perera, MD, an allergist and immunologist and assistant professor of medicine at Columbia University Irving Medical Center in New York City.

When airway inflammation persists over time, she explains, it can lead to scarring and tissue damage. This reduces lung function and elasticity, which can worsen asthma symptoms and make treatments less effective.

Daily difficulties

On a day-to-day basis, uncontrolled eosinophilic asthma can have a significant impact on a person’s quality of life.

This subtype of asthma is associated with a greater risk of asthma attacks, severe symptoms, hospitalization, death, and high-dosage steroid therapy (which come with a host of adverse side effects), Dr. Rothenberg says.

High levels of eosinophils also make it more likely for people to experience issues like frequent sinus and ear infections.

Living with eosinophilic asthma

Today’s treatment options are promising, Dr. Kloepfer says.

“The biologics on the market have helped many patients with eosinophilic asthma begin to lead a normal life and begin participating in activities they were unable to perform previously,” she says.

These therapies also help patients stop taking oral steroids altogether, and steroid side effects can soon resolve or improve.

The outlook for treating eosinophilic asthma may be growing even brighter. Dr. Kloepfer notes that Indiana University is part of the PrecISE study (Precision Interventions for Severe and/or Exacerbation-Prone Asthma)—research funded by the National Institutes of Health that aims to better classify asthma types so that doctors can use precision medicine to help manage severe asthma.