Overview
Secondary hypereosinophilic syndrome (secondary HES) is a condition in which the body produces too many eosinophils — a type of white blood cell that normally helps fight infections and parasites. In secondary HES, the high eosinophil count is caused by another underlying condition rather than arising on its own. Common triggers include parasitic infections, allergic diseases, autoimmune disorders, certain medications, and some cancers (especially lymphomas). When eosinophils build up in large numbers, they can infiltrate and damage organs such as the heart, lungs, skin, nervous system, and digestive tract. Symptoms vary widely depending on which organs are affected. Patients may experience skin rashes, itching, coughing, shortness of breath, abdominal pain, fatigue, fever, and muscle aches. In severe cases, eosinophils can damage the heart muscle, leading to heart failure, or cause blood clots. The condition can range from mild to life-threatening. Treatment focuses on two goals: addressing the underlying cause (such as treating an infection or stopping a triggering medication) and reducing the eosinophil count to prevent organ damage. Corticosteroids like prednisone are the most common first-line treatment. In cases that do not respond well, other medications such as mepolizumab (Nucala), an anti-interleukin-5 antibody approved by the FDA for hypereosinophilic syndrome, may be used. Additional therapies include hydroxyurea and interferon-alpha. Early identification and treatment of the root cause is essential for the best outcomes.
Also known as:
Key symptoms:
Skin rashes or hivesItchingCoughing or wheezingShortness of breathFatigue and weaknessFeverAbdominal pain or diarrheaMuscle achesSwelling in the limbsChest painNumbness or tingling in hands and feetUnexplained weight lossJoint painVision changesSwollen lymph nodes
Sporadic
Usually appears on its own, not inherited from a parent
Variable
Can begin at different ages, from infancy through adulthood
FDA & Trial Timeline
1 eventRigshospitalet, Denmark — PHASE4
Data sourced from FDA regulatory filings and ClinicalTrials.gov. Updated periodically.
Treatments
No FDA-approved treatments are currently listed for Secondary hypereosinophilic syndrome.
1 clinical trialare actively recruiting — trials can provide access to cutting-edge therapies.
View clinical trials →Treatment Centers
8 centersBaylor College of Medicine Rare Disease Center ↗
Baylor College of Medicine
📍 Houston, TX
🏥 NORDStanford Medicine Rare Disease Center ↗
Stanford Medicine
📍 Stanford, CA
🔬 UDNNIH Clinical Center Undiagnosed Diseases Program ↗
National Institutes of Health
📍 Bethesda, MD
🔬 UDNUCLA UDN Clinical Site ↗
UCLA Health
📍 Los Angeles, CA
🔬 UDNBaylor College of Medicine UDN Clinical Site ↗
Baylor College of Medicine
📍 Houston, TX
🔬 UDNHarvard/MGH UDN Clinical Site ↗
Massachusetts General Hospital
📍 Boston, MA
🏥 NORDMayo Clinic Center for Individualized Medicine ↗
Mayo Clinic
📍 Rochester, MN
👤 Mayo Clinic Center for Individualized Medicine
🏥 NORDUCLA Rare Disease Day Program ↗
UCLA Health
📍 Los Angeles, CA
Travel Grants
No travel grants are currently matched to Secondary hypereosinophilic syndrome.
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Caregiver Resources
NORD Caregiver Resources
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Family & Caregiver Grants
Financial assistance programs specifically for caregivers of rare disease patients.
Social Security Disability
Learn how rare disease patients may qualify for SSDI/SSI benefits.
Questions for your doctor
Bring these to your next appointment
- Q1.What is the underlying cause of my high eosinophil count, and how will it be treated?,Which organs are affected, and how will you monitor for organ damage?,What are the risks and side effects of the medications I will be taking?,How often will I need blood tests and follow-up visits?,Are there signs or symptoms I should watch for that would require emergency care?,Is mepolizumab or another biologic therapy an option for me?,What is the long-term outlook for my specific situation?
Common questions about Secondary hypereosinophilic syndrome
What is Secondary hypereosinophilic syndrome?
Secondary hypereosinophilic syndrome (secondary HES) is a condition in which the body produces too many eosinophils — a type of white blood cell that normally helps fight infections and parasites. In secondary HES, the high eosinophil count is caused by another underlying condition rather than arising on its own. Common triggers include parasitic infections, allergic diseases, autoimmune disorders, certain medications, and some cancers (especially lymphomas). When eosinophils build up in large numbers, they can infiltrate and damage organs such as the heart, lungs, skin, nervous system, and di
How is Secondary hypereosinophilic syndrome inherited?
Secondary hypereosinophilic syndrome follows a sporadic inheritance pattern. Genetic counseling can help families understand recurrence risk and testing options.
Are there clinical trials for Secondary hypereosinophilic syndrome?
Yes — 1 recruiting clinical trial is currently listed for Secondary hypereosinophilic syndrome on UniteRare. See the clinical trials section on this page for phase, sponsor, and site details sourced from ClinicalTrials.gov.
Which specialists treat Secondary hypereosinophilic syndrome?
1 specialists and care centers treating Secondary hypereosinophilic syndrome are listed on UniteRare, sourced from ClinicalTrials.gov principal investigators, published research, and the NPPES NPI registry.