Hypereosinophilic syndrome is a rare medical condition caused by an overload of white blood cells called eosinophils. Left untreated, hypereosinophilic syndrome can be life-threatening. Fortunately, prompt diagnosis and treatment mean more than 80% of those diagnosed with hypereosinophilic syndrome are alive five years after diagnosis.
Hypereosinophilic syndrome (HES) is a rare condition caused by an overload of white blood cells called eosinophils. Eosinophils protect your body from parasitic infections and respond to allergens. Normally, eosinophils account for 5% to 7% of your white blood cells, or about 100 to 500 eosinophils per microliter of blood. When you have certain conditions, such as allergies, your eosinophils multiply to cause a condition called eosinophilia.
Hypereosinophilic syndrome happens when eosinophilia accelerates, speeding up eosinophil production and increasing the number of eosinophils. This eosinophil overload can damage your organs, including your heart, lungs, skin and nervous system. Left untreated, hypereosinophilic syndrome can be life-threatening. Fortunately, prompt diagnosis and treatment mean more than 80% of those diagnosed with hypereosinophilic syndrome are alive five years after diagnosis.
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HES is a rare condition, and healthcare providers aren’t sure how many people have HES. Anyone can develop hypereosinophilic syndrome, but it’s most often seen in people ages 20 to 50.
Researchers don’t know all the factors that trigger the dramatic increase in eosinophils that causes most of the cases of hypereosinophilic syndrome. They have, though, identified a few conditions or circumstances that might be responsible:
The most common HES symptom is a rash. Hypereosinophilic symptoms correlate (match to) to the area of your body affected by high eosinophil levels. For example, if your heart has an unusually high level of eosinophils, you might have symptoms of congestive heart failure, cardiomyopathy, myocarditis and pericardial effusion. Likewise, if the eosinophils are congregating in your lungs, you might have recurring (repeating) upper respiratory infections, coughing and difficulty breathing.
Healthcare providers use a process of elimination to diagnose HES. For example, if you have a persistent itchy rash, your healthcare provider would likely do tests to check for certain skin disorders and prescribe treatments for those disorders.
If you’re still having symptoms, your healthcare provider might test your blood for high eosinophil levels. For example, if your symptoms indicate problems with your liver, and your healthcare provider has ruled out other causes, they might perform a liver function blood test. They might also perform a biopsy to confirm a hypereosinophilic syndrome diagnosis.
Healthcare providers focus on reducing the high eosinophil levels in your blood and tissues. Standard treatment includes corticosteroids and chemotherapy drugs.
Unfortunately, researchers don’t know what causes most HES cases or what you can do to prevent it.
Your prognosis, or anticipated outcome, depends on your specific situation. For example, if your condition is linked to a specific cause such as a disorder that affects your bone marrow, your healthcare provider will likely use a treatment that targets your bone marrow disorder.
But if your healthcare provider can’t identify what caused your HES, treatment will focus on your symptoms. Again, for example, if HES targets your lungs, you might have recurrent upper respiratory infections and your treatment will focus on treating your infection.
Generally speaking, the sooner your HES is diagnosed and treated, the less likely you are to have lasting problems.
Healthcare providers usually treat hypereosinophilic syndrome with corticosteroids and chemotherapy. Both treatments have side effects. Talk to your healthcare provider about treatment side effects and what you can do to lessen their impact.
If you’ve been diagnosed with HES, you should contact your healthcare provider if your symptoms persist or get worse.
Hypereosinophilic syndrome affects several organs, including your heart. If HES affects your heart, you should go to the emergency room any time you have symptoms such as chest pain, heartburn, nausea and sweating.
Hypereosinophilic syndrome is a rare medical condition. You’ll probably have questions about its causes and impact. Here are some questions to get you started:
A note from Cleveland Clinic
Hypereosinophilic syndrome (HES) is a rare medical condition that can be difficult to diagnose. If you have HES, you might have been sick and tired for several months with no sure cure in sight. The good news is, once your HES is diagnosed, there are successful treatments for it. And while it might take a few months for your treatment to work, try to be patient — and be sure to talk to your healthcare provider if you’re having trouble coping with the challenges of a long-term illness. They’ll have suggestions for programs and resources for you.
Last reviewed by a Cleveland Clinic medical professional on 03/14/2022.
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Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy