Cookie Notice

This site uses cookies. By continuing to browse this site, you are agreeing to our use of cookies. Review our cookies information for more details.

skip to main content

Hypereosinophilic Syndrome


Hypereosinophilic (hy-per-ee-o-sin-o-FILL-ick) syndrome (HES) is a group of rare blood disorders. It occurs when an individual's blood has very high numbers of eosinophils. An eosinophil is a type of white blood cell that plays an important role in the immune system.

Most people have less than 500 eosinophils/microliter in their blood. People with HES usually have more than 1,500 eosinophils/microliter in their blood for 6 months or more, and the cause cannot be identified.

These eosinophils make their way into various tissues, causing inflammation and eventually organ dysfunction. The most commonly involved organs in HES include the skin, lungs, heart and nervous system.

Symptoms & Diagnosis

HES can happen at any age, although it is more common in adults. People with HES may suffer from a wide variety of symptoms, depending upon which parts of the body are affected. These symptoms include:

  • Skin rashes such as urticaria or angioedema
  • Dizziness
  • Memory loss or confusion
  • Cough
  • Shortness of breath
  • Fatigue
  • Fever
  • Mouth sores

Symptoms of HES are also common in many other medical problems, making an initial diagnosis more difficult. The first step is to rule out other conditions with similar symptoms. These include parasitic infection, allergic disease, cancers, autoimmune diseases and drug reactions.

An allergist / immunologist has specialized training to effectively diagnose the problem and, if HES is present, to work collaboratively with other specialists such as a hematologist or cardiologist in the treatment and monitoring of HES.

Testing is individualized according to symptoms and may include stool evaluation to detect parasitic infection, allergy testing to diagnose environmental or food allergies, biopsies of the skin or other organs, blood tests to screen for autoimmunity or CT imaging of affected organs, molecular genetic studies to detect FIP1L1-PDGFRA or other mutations to help determine, diagnosis, prognosis, and treatment.

When diagnosed with HES, it is important to determine the extent of organ damage. A chest x-ray and echocardiogram are routinely performed to evaluate the heart and lungs. Other tests often performed in HES patients include liver and kidney function, serum vitamin B12 levels, erythrocyte sedimentation rate (ESR) and serum tryptase levels.

Treatment & Management

The goal of HES treatment is to reduce eosinophil levels in the blood and tissues, thereby preventing tissue damage–especially in the heart. Standard HES treatment includes glucocorticosteroid medications such as prednisone, and chemotherapeutic agents such as hydroxyurea, chlorambucil and vincristine. Interferon-alpha may also be used as a treatment. This medication must be administered by frequent injections.

Research is uncovering new therapies for HES. One new approach for controlling malignant cell growth is the use of tyrosine kinase inhibitors such as GleevecTM (imatinib). Monoclonal antibody therapy, such as alemtuzumab (anti-CD52) has also shown promise for treatment of HES. In fact, based on a recent phase III randomized, placebo-controlled trial1, the monocloncal antibody Nucala or mepolizumab (anti-IL-5) has just received approval by the U.S. Food and Drug Administration for treatment of adults and children aged 12 years and older with HES for six months or longer without another identifiable non-blood related cause of the disease.

The prognosis of HES depends upon the extent of any organ damage. In very severe cases, HES may be fatal, but there is hope. Survival rates have improved greatly. In 1975, only 12% of HES patients survived three years. Today, more than 80% of HES patients survive five years or more.

1. Roufosse F, Kahn J-E, Rothenberg ME, Wardlaw AJ, Klion AD, Kirby SY, Gilson MJ, Bentley JH, Bradford ES, Yancey SW, Steinfeld J, Gleich GJ, Efficacy and safety of mepolizumab in hypereosinophilic syndrome: a Phase III, randomized, placebo-controlled trial, Journal of Allergy and Clinical Immunology (2020), doi:

Keep pace with the latest information and connect with others. Join us on Facebook and Twitter.

This article has been reviewed by Andrew Moore, MD, FAAAAI

Reviewed: 9/28/20