Eosinophils are an important part of your immune system, but too many of these white blood cells can result in rare blood disorders, collectively known as hypereosinophilic syndrome.
Your immune system is made up of different types of specialized cells that all work together to defend against infection and promote the healing process.
These cells include eosinophils, a type of white blood cell that originates in your bone marrow. During a typical immune response, your body sends eosinophils to sites of inflammation, where they release inflammatory mediators, which are substances intended to fight infection.
However, it’s possible for your body to produce too many eosinophils, resulting in a group of blood disorders known as hypereosinophilic syndrome (HES). In people with HES, these extra eosinophils start damaging nearby tissue and organs, resulting in a range of potential symptoms.
HES symptoms can vary greatly from person to person, depending on the organs and body systems involved.
Potential early symptoms of HES include:
- shortness of breath
- skin rashes
- memory loss
- mouth sores
- weight loss
Later symptoms will also depend on the organs and body systems involved.
HES vs. hypereosinophilia
It’s possible to have elevated eosinophils and not be living with HES. A too-high eosinophil level that can be attributed to other causes, like infection, is known as eosinophilia.
It only becomes HES when no underlying factor can be identified.
There are three main types of HES, each related to a different underlying cause.
- Myeloproliferative (also known as primary or clonal HES): This type results from the overproduction of eosinophils in the bone marrow and elevated serum levels of tryptase, an enzyme that indicates mast cell activation. Genetics likely play a role in this type of HES.
- Lymphocytic (also known as reactive HES): This type is caused by an underlying condition, such as an infection or cancer, that results in an increase of lymphocyte cytokines (substances that signal eosinophils).
- Idiopathic: HES is considered idiopathic when there’s no identified cause.
Experts are still trying to better understand the exact causes and processes behind each type of HES.
If a healthcare professional suspects you may have HES, they’ll start with ordering a blood test to measure your eosinophil levels if this hasn’t already been done.
HES involves elevated levels of eosinophils over a long period of time, typically 6 months or longer. The average person has fewer than 500 eosinophils per milliliter (mL) of blood. In people with HES, eosinophil levels tend to be greater than 1,500 eosinophils/mL.
Next, your care team will want to rule out other causes of high levels of eosinophils, such as:
- viral, bacterial, or parasitic infection
- allergic disease
- drug/chemical reactions
- autoimmune disease
- abnormal tissue growth or cancer
Ruling out the above will likely involve additional testing, including allergy testing, more blood tests, or fecal exams. All these potential causes come with their own set of tests.
Once these alternate cases have been ruled out, you might be referred to additional testing, including::
- liver/kidney function blood tests
- tryptase level check
- vitamin B12 check
- genetic testing
Depending on your symptoms and test results, your care team might also use specific diagnostic screening tools, such as ordering X-rays and ultrasounds, to assess any organ damage.
There’s currently no cure for HES, but treating the condition can help prevent organ damage and slow disease progression.
The main goal of HES treatment is lowering the number of eosinophils in your body. How this is achieved will depend on the organs and body systems involved, how advanced your condition is, and your overall health.
Most cases of HES are treated using glucocorticosteroids like prednisone and chemotherapeutic medications like chlorambucil. These agents suppress the body’s immune response, quickly reducing eosinophil levels.
Your healthcare team may also prescribe regular injections of interferon-alpha, another medication that can temporarily decrease your white blood cell levels.
Depending on how your body reacts to these treatments, your healthcare team may recommend additional therapies, such as:
- tyrosine kinase inhibitors
- monoclonal antibodies
- systemic steroids for widespread symptoms like skin rashes
Hypereosinophilic syndrome occurs when your body has elevated eosinophil levels. While there’s no cure for HES, treatment can help prevent organ damage and disease progression by keeping eosinophils at more manageable levels.