Hypereosinophilic Syndrome: Causes, Symptoms, and Treatment
Medically reviewed by Harsha Moole, MD, Internal Medicine. Last reviewed: October 23, 2026.
What kind of doctor treats Hypereosinophilic Syndrome?
An allergist-immunologist, a doctor who treats immune system problems, often diagnoses hypereosinophilic syndrome. This doctor works with other specialists, such as a hematologist (a blood doctor) or a cardiologist (a heart doctor). A direct primary care or concierge doctor can be a first stop for an evaluation and can refer you to a specialist when needed.
What is hypereosinophilic syndrome?
Hypereosinophilic syndrome (HES) is a group of rare blood disorders. It happens when the 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.
The extra eosinophils move into tissues and cause inflammation (swelling). Over time, organs may stop working well. The organs most often affected are the skin, lungs, heart, and nervous system. Most people have fewer than 500 eosinophils per microliter of blood. People with HES usually have more than 1,500 per microliter.
Symptoms
Symptoms depend on which organs are affected. Common symptoms include:
- Tiredness, fever, muscle pain, and night sweats.
- Skin problems such as eczema, hives, and swelling under the skin.
- Cough, wheezing, and shortness of breath.
- Weight loss, trouble swallowing, belly pain, nausea, vomiting, diarrhea, and mouth sores.
- Numbness or tingling in the hands or feet, muscle weakness, confusion, memory loss, or a stroke or ministroke.
- Heart problems, which can cause shortness of breath and palpitations (a racing or pounding heartbeat).
Some people have no symptoms. Their only sign is a high eosinophil level on a blood test.
Causes and who gets it
HES has several types, based on the cause. Secondary (reactive) HES is the most common type. It occurs in response to an infection, an inflammatory process, or a drug. Infection with parasitic worms can cause it. Certain cancers can also trigger it.
Primary (myeloid) HES comes from gene changes that lead to too many eosinophils. These changes are new in the affected person and are not inherited. In the lymphocytic type, abnormal T cells, a type of immune cell, release substances that cause extra eosinophils.
A familial type of HES can also occur. In some people, no cause can be found. HES can occur at any age, but it is more likely in people between 20 and 50 years old.
How doctors diagnose it
Symptoms of HES are common in many other problems, so doctors first rule out other causes. These include parasitic infection, allergic disease, cancers, autoimmune diseases, and drug reactions. A diagnosis needs a count above 1,500 per microliter on at least two blood tests taken at least one month apart.
Other tests depend on your symptoms. They may include:
- A complete blood count and a blood smear.
- A stool test for parasite eggs, if a parasite infection is possible.
- An electrocardiogram and an echocardiogram to check the heart.
- A biopsy (a small tissue sample) of an affected organ or the skin.
- A bone marrow biopsy, which removes a small sample of bone marrow, the spongy tissue inside the bone.
Treatment
The goal is to lower eosinophil levels, stop organ damage from getting worse, and ease symptoms. Treatment depends on the type of HES and how severe it is. People with familial HES and no symptoms may only need to be watched closely. Antiparasitic medicines can treat HES caused by parasites. HES caused by a drug can be treated by stopping that drug. Follow your doctor's instructions before you stop any medicine.
For most other cases, steroids (glucocorticoids) are the first treatment to try. Imatinib is the preferred treatment for myeloid HES with certain gene changes. If people with non-myeloid HES do not improve with steroids, imatinib may be recommended as well. Hydroxyurea can also be used as a second option.
Mepolizumab targets interleukin-5, a protein released by immune cells. It can help people on steroids use less steroid and have fewer steroid side effects. The FDA has approved mepolizumab for adults and children aged 12 and older with HES that has no other identifiable cause outside the blood. The FDA has also approved benralizumab (Fasenra) for people aged 12 and older with HES who do not have an identifiable non-blood-related cause.
People with blood clots usually get blood thinners. A stem cell transplant is a last resort for HES that does not respond to other treatment, and it is considered risky.
When to see a doctor
See a doctor if a blood test shows a high eosinophil count, even if you feel fine. Heart involvement in HES can be fatal. Call 911 or go to the emergency room if you have chest pain or severe trouble breathing. Do the same for sudden confusion, sudden weakness, or trouble speaking, which can be signs of a stroke.
How a direct primary care or concierge doctor fits in
A direct primary care doctor charges a flat monthly fee instead of billing insurance, while a concierge doctor usually charges more and often works alongside insurance. Such a doctor can order first blood tests, review your results, and help coordinate care with an allergist, a hematologist, or a cardiologist.
Common questions
Is hypereosinophilic syndrome a type of cancer?
Not always. The most common type, secondary HES, is a reaction to an infection, inflammation, or a drug. Chronic eosinophilic leukemia is classified as a type of myeloid HES.
Can you have hypereosinophilic syndrome without symptoms?
Yes, some people have no symptoms.
Can hypereosinophilic syndrome be life threatening?
Yes, in very severe cases.
Does hypereosinophilic syndrome run in families?
Yes, sometimes, through a type called familial HES. In myeloid HES, the gene changes are new in the person and are not inherited.
Sources
- NORD - Hypereosinophilic Syndrome
- American Academy of Allergy, Asthma and Immunology - Hypereosinophilic Syndrome Symptoms, Diagnosis, Treatment and Management
Medical Disclaimer
This content is for general educational and informational purposes only and is not medical advice. It is not a substitute for professional medical advice, diagnosis, or treatment, and reading it does not create a doctor-patient relationship. Always seek the advice of your physician or another qualified health provider with any questions about a medical condition, and never disregard or delay seeking professional advice because of something you read here. If you think you may have a medical emergency, call 911 (or your local emergency number) immediately.
