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  • Reviewed on 7/12
    By Dr. Truong

Hypereosinophilic Syndromes

Hypereosinophilic syndromes (HES) are types of disorders that happen when eosinophils (white blood cells) are overproduced by a person’s body. These white blood cells then attack organ systems like the skin, lungs, brain/nerves and heart. This can result in illness due to these organs not working properly. Some specific genetic abnormalities have been discovered as the underlying cause of some hypereosinophilic syndromes, but in many cases a specific cause cannot be identified. In these cases, the diagnosis is called idiopathic (unknown) hypereosinophilic syndrome.


Symptoms of HES depend on which organs are involved. Some typical symptoms include:

  • a skin rash,
  • cough and breathlessness,
  • abdominal pain,
  • diarrhea/vomiting, and
  • weight loss.

Cardiovascular problems may include:

  • cardiac arrhythmia (abnormal heartbeat),
  • cardiac dysfunction causing shortness of breath or accumulation of fluid that causes swelling (edema), and
  • blood clots in the heart.

In its early stages, the symptoms of HES can be silent and not easily detected.

If the doctor is concerned about the number of eosinophils in the blood, he or she may order more blood tests. Depending on the person's physical exam, initial bloodwork and symptoms, the doctor may order specific tests to evaluate organ function, such as an electrocardiogram (ECG), echocardiogram, pulmonary function tests, abdominal CT, chest CT or chest x-ray, as well as possibly tissue biopsies done at body sites for which there is suspected involvement. A hematologic evaluation is often necessary to rule out other causes of hypereosinophilia, such as a blood cancer, as well as to evaluate for some of the known causes for HES.


Test results will be reviewed by the doctor to decide if the condition is in fact HES. These criteria are:

  1. Eosinophil count in the blood greater than or equal to 1500/microliter, and lasting for more than 6 months
  2. Signs and/or symptoms of organs not working properly due to white blood cells attacking the organs, and
  3. No other apparent explanations for the increased white blood cells, such as parasitic infection or allergic disease. If vital organs like the heart or bone marrow are not working properly and it’s happening quickly, a doctor will not wait 6 months before diagnosing and considering prompt treatment for the HES.



Treatment of HES depends upon many factors:

  • whether there was an identified known cause,
  • which organs are involved, and
  • the degree to which the organ(s) are involved.  

Medications for the treatment of HES may include:

  • Prednisone (by mouth)
  • Methylprednisolone [via intravenous (IV)]
  • Other drugs to prevent the white blood cells from multiplying (hydroxyurea, interferon-alpha) and to decrease the long-term use of prednisone or methylprednisolone
  • Some medications such as imatinib (Gleevec®) are expected to work in only certain forms of HES. Some medications such as mepolizumab (which would prevent the growth of white blood cells) is likely to help many patients with HES when it gets FDA approval and becomes available in the market.


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Doctors Who Treat Hypereosinophilic Syndromes

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