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What is HES?

• Idiopathic Hypereosinophilic Syndrome (HES) is a rare group of disorders characterized by persistent and marked buildup of a type of white blood cell (eosinophil) in the blood and tissue, for no apparent reason. The overabundance of eosinophils can lead to complications ranging from fever and fatigue to blood abnormalities, respiratory, cardiac, skin and gastrointestinal problems or death in some people with advanced disease.
• Although the exact prevalence of idiopathic HES is unknown, current estimates suggest that HES affects between 2,000 and 5,000 individuals in the United States. The condition is more common in men than women, and although the age of onset is variable, diagnosis generally occurs between the ages of 20 and 50.
• In a healthy body, eosinophils are enlisted in the defense against parasites and are also involved in allergic responses. In people with idiopathic HES, the production of eosinophils is sharply increased, and large numbers of these cells enter the bloodstream and may infiltrate different tissues of the body, most commonly the blood, heart, skin, lungs, kidneys, liver, and gastrointestinal tract. These eosinophils are typically highly activated and thereby cause inflammatory damage to infiltrated organs.

Diagnosis of HES

• The diagnosis of HES can be difficult as symptoms are often variable and may overlap with other conditions. People with HES may show a wide range of non-specific symptoms such as fatigue, cough, rash, and fever; or may experience life-threatening cardiac symptoms. Because these symptoms can mimic many other diseases, it may take several months to years before a definitive diagnosis of HES is made.
• Early recognition of the disease and evaluation for treatment are critical, because complications of HES can be severe or even fatal in some cases. Heart-related symptoms are the major cause of death and disability in people with HES.
• Diagnostic Criteria:
  • Blood eosinophil count >1500/uL for >6 months
  • Eosinophilia-related organ dysfunction
  • Exclusion of secondary causes of eosinophilia (e.g., parasitic infection or allergic reaction)

• Systemic corticosteroids are commonly prescribed therapy, but long-term use is limited by potentially serious side-effects.
• Tyrosine Kinase Inhibitors are a type of medication that is used primarily to treat cancers, but have also been found to be effective in some patients with HES.
• Second-line options include cytotoxic and immunomodulatory agents. These agents have limitations in terms of safety and tolerability.

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