Asthma Subgroups: What Is Persistent Eosinophilic Asthma?
Another rare subgroup of asthma is persistent eosinophilic asthma. It’s a subgroup of asthma usually diagnosed in adulthood that is associated with a combination of severe asthma, eosinophilia, chronic sinusitis, and nasal polyps. So, what does all this mean?
What is late onset eosinophilic asthma?
As noted, it’s a combination of:
- Severe Asthma. About 15% of asthmatics have difficulty controlling asthma despite high doses of inhaled corticosteroids and frequent bursts of systemic steroids. About 50-60% of severe asthmatics have eosinophilic asthma, so it’s a significant cause of severe asthma.1
- Eosinophilia. It’s a high eosinophil level in either blood or sputum, as determined by a blood or sputum test. Tissue can also be obtained by a procedure called bronchoscopy, where a tube is inserted into your airway after you are sedated. It is commonly present when asthma is uncontrolled or severe.2,4
- Chronic sinusitis. This is a sinus infection that always seems to be present. It is associated with a stuffy nose, nasal drainage (which can also be tested for eosinophilia), and anosmia (loss of sense of smell).
- Nasal polyps. It’s a soft, painless stalk of skin that hangs down from the roof of your nasal passages blocking the flow of air.5,6
- Eosinophilic Otitis media. Sometimes this is also diagnosed. It’s an infection of the inner ear caused by eosinophilia and resulting in thick yellow effusion and gradual loss of hearing. It is generally only diagnosed in people with asthma and is resistant to traditional medicines used to treat otitis media.7,8
So, to understand this rare subgroup of asthma, we must have a basic understanding of what eosinophils are, along with their role in asthma.
Eosinophils are responsible for about 50% of all cases of asthma, particularly childhood-onset and allergic asthma (extrinsic). They are white blood cells (leukocytes) made in the bone marrow that are summoned to your airway during asthma attacks. When they come into contact with airway cells they release their contents, which include chemicals that cause both upper and lower airway inflammation, meaning the sinuses, nasal passages, and lower airways.7,9,11
It's defined when eosinophils in the sputum represent greater than 2% of inflammatory cells for five consecutive years.13 It is sometimes diagnosed in childhood, although it's most often diagnosed in adulthood, which is why it is often referred to as Late or Adult-Onset Persistent Eosinophilic Asthma.
Lower airway inflammation
Asthma is considered a disease associated with some degree of chronic (it’s always there) underlying airway inflammation. This makes your airways twitchy to asthma triggers, exposure to which cause asthma symptoms. Eosinophils play a key role in this inflammation and are probably responsible for it becoming chronic.
Steroids suppress the chemicals responsible for eosinophil recruitment and also cause eosinophils to die (called apoptosis). This reduces eosinophil counts, reduces airway inflammation, and makes airways less twitchy. This results in improved asthma control.7,13
Childhood-onset allergic asthma and adult-onset eosinophilic asthma both present with eosinophilia. However, most cases of childhood-onset allergic asthma respond well to low doses of inhaled corticosteroids, while most people with persistent eosinophilic asthma respond poorly to low doses of inhaled corticosteroids. This means that allergic asthma is easier to control than eosinophilic asthma. What causes this difference between early and late-onset asthma is unknown.13
This means that most cases of late-onset eosinophilic asthma are associated with persistent eosinophilia despite the highest doses of inhaled corticosteroids and frequent boosts of systemic steroids. This means they have severe asthma.7
Digging deeper into eosinophilic asthma
A sputum sample can be easily obtained and taken to a laboratory where eosinophil cells can be counted. For most asthmatics, sputum eosinophils are elevated when asthma gets worse and decrease when asthma improves, such as when corticosteroids are used. Persistent sputum eosinophilia despite the highest doses of steroids is the best indicator of persistent eosinophilic asthma.4,11,12
Upper airway inflammation
Eosinophils are known to infiltrate tissues of the upper as well as the lower airways, this may lead to sinus infections, nasal polyps, and eosinophilic otitis media, all of which are very difficult to treat, and may require a referral to an ear, nose, and throat (ENT) doctor. Antibiotics may help with sinusitis. Systemic corticosteroids (prednisone) may help with otitis media. Even following surgery to remove nasal polyps, they often grow back, and sometimes quickly.7,10
Eosinophils may be abnormally elevated due to the presence of certain asthma genes. These genes, or gene mutations, may encode proteins that tell immune cells to produce in abundance chemicals responsible for eosinophil recruitment. Researchers have theories to explain the exact mechanism involved, which I may discuss in a future post.
Early diagnosis of eosinophilic asthma is important, as prolonged and untreated airway inflammation may lead to lung scarring or an abnormal thickening of airway walls. Chemicals released by eosinophils may also play a role in airway scarring. This causes permanent airway narrowing, resulting in asthma that is only partially reversible. This may sometimes be confused with Chronic Obstructive Lung Disease (COPD).1,7,11
Similar to COPD, some shortness of breath may be present even on a good asthma day. This may cause a blunted sense of shortness of breath. When asked how they feel, even though you may observe the signs of asthma, they may say, “I feel fine.” This is something their doctors have to watch out for. Rather than using symptoms monitoring to decide what actions to take, they may be better off using peak flow monitoring.7
Other overlapping subgroups
There are other asthma subgroups that may overlap with eosinophilic asthma, and these include allergic asthma (sometimes) and Aspirin Exacerbated Respiratory Disease (frequently). It may also be associated with allergic bronchopulmonary aspergillosis and Churg–Strauss syndrome.11
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