ConditionBlood & immune system
Hypereosinophilic Syndrome (HES)
Hypereosinophilic syndrome (HES) is a rare group of blood disorders in which the body makes too many eosinophils, a type of white blood cell, and they damage organs. It is defined by a persistently high eosinophil count, at least 1,500 cells per microliter on two occasions, with evidence of organ damage and no other explanation such as parasites, allergy or drugs. It can affect the skin, lungs, heart, nerves and gut. Treatment with steroids, targeted drugs such as imatinib or mepolizumab, and other medicines controls it in most people.
Also called: HES, idiopathic hypereosinophilic syndrome, hypereosinophilia with organ damage
At a glance
- What it is
- Persistently high eosinophils (1,500 or more per microliter) causing organ damage.
- Types
- Myeloproliferative (including FIP1L1-PDGFRA), lymphocytic, familial and idiopathic.
- Organs affected
- Skin, lungs, heart, nerves, gut, blood vessels.
- Diagnosis
- Blood counts, ruling out other causes, bone marrow tests, genetic and organ tests.
- Treatment
- Steroids, imatinib for PDGFRA-positive disease, mepolizumab, hydroxyurea and others.
When to get help
Call 911 or go to the ER
- Chest pain, severe breathlessness, fainting or a racing heartbeat (possible heart involvement)
- Sudden weakness on one side, trouble speaking or vision loss (possible stroke from a blood clot)
- A painful, cold, pale leg or arm (possible clot)
See a doctor within a day or two
- New breathlessness, swelling of the legs, or reduced exercise tolerance in someone with high eosinophils
- Numbness, tingling or weakness in the hands or feet
- Persistent fever, weight loss or night sweats with a high eosinophil count
Book a routine appointment
- An eosinophil count of 1,500 or more found on a routine blood test
- Long-lasting itchy rash, hives or swelling without a clear allergic cause
- Chronic cough, wheezing or diarrhea with high eosinophils
What eosinophils do
Eosinophils are white blood cells that help fight parasites and take part in allergic reactions. A normal blood count is usually below about 500 cells per microliter. Eosinophils release toxic proteins and inflammatory chemicals. When they build up in tissues for a long time, these substances damage organs.
Raised eosinophils (eosinophilia) are most often caused by allergies, asthma, eczema, parasitic infections and drug reactions. HES is diagnosed only when these are ruled out.
Types of HES
| Type | Description |
|---|---|
| Myeloproliferative HES | Bone marrow disorder. Includes FIP1L1-PDGFRA gene fusion, more common in men, responds very well to imatinib |
| Lymphocytic HES | Abnormal T cells produce signals that drive eosinophil production. Often skin symptoms |
| Familial HES | Rare, inherited |
| Idiopathic HES | No cause found. The most common category |
| Overlap and associated | Eosinophilia linked to conditions such as eosinophilic granulomatosis with polyangiitis (Churg-Strauss syndrome) or inflammatory bowel disease |
Symptoms
Symptoms depend on which organs are affected:
- General: tiredness, fever, weight loss, night sweats, muscle aches
- Skin: itchy rash, hives, swelling (angioedema), nodules
- Lungs: cough, wheezing, shortness of breath
- Heart: inflammation and scarring of the heart lining (endomyocardial fibrosis), leading to restrictive cardiomyopathy, heart valve leaks, blood clots in the heart and heart failure. Heart involvement is the most serious complication
- Nerves: numbness, tingling, weakness, confusion, and strokes from clots
- Gut: belly pain, diarrhea, vomiting
- Blood: a tendency to form clots, enlarged spleen
Diagnosis
- Blood count: eosinophils of 1,500 per microliter or more on two tests at least a month apart.
- Ruling out other causes: allergy history, medicine review, stool tests and blood tests for parasites (such as Strongyloides, which must be treated before giving steroids), and tests for vasculitis and cancer.
- Organ assessment: troponin and echocardiogram or cardiac MRI for the heart, lung function tests and CT, nerve studies, and biopsies of affected tissue.
- Bone marrow biopsy and genetic testing: looking for FIP1L1-PDGFRA and other mutations, and markers of blood cancers.
- T-cell studies for lymphocytic HES.
- Vitamin B12 and tryptase levels, which are often raised in myeloproliferative forms.
Treatment
The goal is to lower eosinophil counts and prevent organ damage.
- Imatinib: a targeted pill that is highly effective for FIP1L1-PDGFRA-positive HES, often leading to complete remission at low doses.
- Corticosteroids: first-line for most other forms. Many people respond within days.
- Mepolizumab: an antibody that blocks IL-5, the main signal for eosinophil growth. It is FDA-approved for HES and reduces flares and steroid needs.
- Other options: hydroxyurea, interferon-alpha, other targeted drugs, and in severe resistant cases, stem cell transplant.
- Anticoagulants for blood clots.
- Heart treatments, including valve surgery, when needed.
- Strongyloides treatment (ivermectin) before steroids in people at risk.
Outlook
Outlook has improved greatly with targeted therapies. Many people live normal lifespans with treatment and monitoring. Heart involvement and resistant disease are the main factors linked to worse outcomes. Regular blood counts and heart checks are important.
Frequently asked questions
What is hypereosinophilic syndrome?
Hypereosinophilic syndrome is a rare disorder in which the body makes too many eosinophils, a type of white blood cell, and they damage organs such as the heart, lungs, skin and nerves. It is diagnosed when counts stay at 1,500 or more per microliter with organ damage and no other cause.
What causes high eosinophils?
The most common causes are allergies, asthma, eczema, parasitic infections and drug reactions. Less common causes include autoimmune diseases, vasculitis and some cancers. Hypereosinophilic syndrome is considered only after these are ruled out.
What are the symptoms of hypereosinophilic syndrome?
Symptoms vary but often include tiredness, rash and itching, cough, wheezing, breathlessness, numbness or tingling, and digestive symptoms. Heart involvement can cause chest pain, swelling and heart failure. Some people have no symptoms when high eosinophils are first found.
How is hypereosinophilic syndrome treated?
Treatment depends on the type. FIP1L1-PDGFRA-positive disease responds very well to imatinib. Other forms are usually treated with corticosteroids, often with mepolizumab, hydroxyurea or interferon to control counts and reduce steroid use. Regular monitoring protects the heart and other organs.
Sources
This guide was written from current patient and clinical guidance, including:
- American Society of Hematology: Hypereosinophilic syndromes
- National Institute of Allergy and Infectious Diseases (NIAID): Hypereosinophilic syndrome
- World Health Organization classification of myeloid and lymphoid neoplasms with eosinophilia
- American Partnership for Eosinophilic Disorders (APFED): Hypereosinophilic syndrome
- MedlinePlus: Eosinophil count