Hypereosinophilic Syndrome

Eosinophils are types of white blood cells which are part of our normal immune system. They tend to be elevated in allergic disorders. Eosinophils also play an important role in protecting us from certain infections and infestations from parasitic organisms.

Hypereosinophilic syndrome (HES) refers to a condition where there are excessive numbers of eosinophils in the bloodstream. Normally there are less than 500 eosinophils per microliter of blood. HES is defined as having equal or more than 1,500 eosinophils per microliter consistently for more than 6 months.

Though we need eosinophils for defending us from microbes and helminths (i.e., parasitic worms), excessive numbers can be deleterious. These cells accumulate in tissues and cause inflammation. The resultant inflammation may lead to dysfunction of various organs. The most common organs that are typically affected are the skin, heart, lungs, bone marrow, gastrointestinal tract, and nervous system.

The exact prevalence of this condition is unknown however, it is estimated to occur in between 1 and 9 persons per 100,000 population. It is found equally in both sexes and is most common in middle-aged individuals, though it can occur in any age group.


Certain genetic abnormalities in chromosome 4 were observed in some affected individuals. Infestations by helminths (e.g., roundworm, hookworm) could be a trigger for this condition in a few individuals. In a vast majority of cases however, no cause can be identified. When no cause is recognized, the condition is called idiopathic hypereosinophilic syndrome.


The organ system and corresponding symptoms of hypereosinophilic syndrome may include the following:


The diagnostic tests are individualized according to the particular symptoms of the patient and may include:

  • Blood test to screen for number of eosinophils
  • Stool evaluation to detect a parasitic infection
  • Allergy testing to diagnose environmental, medication, and/or food allergies
  • Biopsies of the skin or other organs
  • Blood tests to screen for autoimmunity
  • CT imaging of the affected organs
  • Genetic and molecular studies
  • Chest X-ray and echocardiogram
  • Liver and kidney function tests
  • Serum tryptase levels
  • Miscellaneous tests to evaluate for cancers


The treatment for hypereosinophilic syndrome is aimed at reducing the numbers of eosinophils in order to prevent or restrict tissue damage and preserve organ function. Some of the medications that are used to treat HES may include:

  • Corticosteroids: Prednisone, dexamethasone
  • Chemotherapeutic agents: Hydroxyurea, chlorambucil, vincristine
  • Cytokines: Interferon alpha
  • Tyrosine kinase inhibitors: Gleevec (i.e., imatinib) is also used to treat acute lymphocytic leukemia and chronic myelogenous leukemia that are Philadelphia chromosome-positive, certain types of gastrointestinal stromal tumors, chronic eosinophilic leukemia, systemic mastocytosis, and myelodysplastic syndrome.
  • Monoclonal antibodies: Nucala (i.e., mepolizumab was approved by the FDA for the treatment of hypereosinophilic syndrome in the last week of September 2020 for patients 12 years of age and above at the dose of 300 mg. subcutaneous injection every 4 weeks.


The outlook for hypereosinophilic syndrome has improved significantly in recent years. In 1975, only 12% of HES patients survived 3 years. Today in 2020, more than 80% of HES patients survive 5 years or more.

The board certified allergists of Black & Kletz Allergy have been diagnosing and treating both adults and children in the Washington, DC, Northern VA, and Maryland metropolitan area for over 5 decades. We have offices in Washington, DC, McLean, VA (Tysons Corner, VA), and Manassas, VA. There is on-site parking at all of the offices. The Washington, DC and McLean, VA office locations are Metro accessible and there is a free shuttle that runs between our McLean office and the Spring Hill metro station on the silver line. Our allergy doctors of Black & Kletz Allergy specialize in all types of allergic conditions including hypereosinophilic syndrome. They are also experts in the treatment of allergic rhinitis (i.e., hay fever), asthma, sinus disease, hives (i.e., urticaria) , eczema (atopic dermatitis), swelling problems, medication and food allergies, and immunological disorders. If you would like to schedule an appointment, please call us or alternatively you can click Request an Appointment and we will respond back to you within 24 hours on the next business day. Our goal at Black & Kletz Allergy is to serve the greater Washington, DC metropolitan community with top-notch allergy care with boundless dedication and great pride as we have done for many years.