Hypereosinophilic (hy-per-ee-o-SIN-o-phil-ik) syndrome (HES) refers to a group of blood disorders that occur when you have high numbers of eosinophils — white blood cells that play an important role in your immune system. Over time, these high numbers of eosinophils enter various tissues, causing inflammation and eventually damaging your organs, most commonly targeting the skin, lung, heart, blood and nervous system. Hypereosinophilic syndrome can become life-threatening if not treated.

HES can affect anyone, but it occurs more often in men, usually between 20 and 50 years of age. Symptoms of HES vary, depending on what part of your body is affected. Skin symptoms include itching and rashes, for example. If your lungs are affected, you may be short of breath and have a cough.

  • A team approach. Mayo Clinic doctors from several medical specialties work together to provide you with the best care possible for hypereosinophilic syndrome. Your team may include specialists in allergic diseases, dermatology, gastroenterology, pediatrics, neurology, endocrinology, hematology and pathology.
  • Specialization. The Allergic Diseases Research Laboratory at Mayo Clinic has been actively studying eosinophil biology for almost 50 years, aiming to understand the role of eosinophils in diseases like hypereosinophilic syndrome.
  • Cutting-edge medicine. The Allergic Diseases Research Laboratory has had a National Institutes of Health grant in allergic diseases since the 1980s and provides training for doctors from many medical disciplines, with the goals of finding new treatments and eventually curing diseases like hypereosinophilic syndrome.

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Doctors trained in allergic diseases, dermatology, gastroenterology, pediatrics, neurology, endocrinology, hematology and pathology care for people with hypereosinophilic syndrome at Mayo Clinic in Minnesota.

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The initial goal in diagnosing hypereosinophilic syndrome is to rule out other disorders that can elevate your eosinophil count — such as a parasitic infection, allergic disease or drug reaction. Provide your travel history and a list of any medications you're taking to your doctor.

Ruling out other conditions

Your symptoms determine what types of tests will be recommended for a diagnosis. Some tests to rule out other conditions include:

  • Blood tests. Blood tests may reveal autoimmunities, parasitic infections, or impaired liver or kidney function.
  • Allergy tests. Environmental or food allergies can elevate your eosinophil count.
  • Stool tests. Stool evaluations can detect parasitic infections that affect your eosinophil count, such as hookworm.
  • Imaging tests. Chest X-rays, computerized tomography (CT) scans and echocardiograms help evaluate the condition of your heart, abdomen and lungs.

Determining the cause of your HES

If you've been diagnosed with HES, these tests may help determine the cause:

  • Blood screening. This test can reveal a genetic mutation known as FIP1L1-PDGFRA, which can cause hypereosinophilic syndrome.
  • Bone marrow biopsy. If your blood screen is negative for a genetic mutation, this test may be considered. Biopsies are also useful because they help exclude the possibility of other conditions.

The goal of treatment for hypereosinophilic syndrome is to reduce the numbers of eosinophils in your body and prevent tissue damage, especially to your heart. Your treatment depends on your symptoms, the severity of your condition and the cause of your HES.

  • Watchful waiting. If you have no symptoms and your eosinophil count is low enough, your doctor may opt for a "wait and see" approach. Your condition will then be closely monitored for any changes related to HES.
  • Prednisone. Generally, if you don't have the FIP1L1-PDGFRA gene mutation, you'll initially be treated with prednisone, a corticosteroid, which is gradually tapered to the lowest dose that controls the eosinophil count. If a high dose of prednisone is needed, other medications are added to control hypereosinophilic syndrome and to avoid the side effects of high-dose prednisone. Prednisone side effects include psychiatric problems, high blood pressure and increased susceptibility to infection.
  • Protein-tyrosine kinase inhibitor. If you have the FIP1L1-PDGFRA gene mutation, you have, by definition, chronic eosinophilic leukemia. You'll need treatment with imatinib mesylate (Gleevec), a type of drug known as a protein-tyrosine kinase inhibitor. Imatinib mesylate slows the growth of cancer cells and is almost 100 percent effective, especially for men.

Doctors trained in eosinophil biology and other areas conduct basic and clinical research in potential diagnostic tests and treatments for hypereosinophilic syndrome. Staff in the Allergic Diseases Research Laboratory at Mayo Clinic in Minnesota conduct research in hypereosinophilic syndrome and other eosinophil-related disorders.


See a list of publications by Mayo authors on PubMed, a service of the National Library of Medicine.

Nov. 19, 2012