Hypereosinophilic Syndrome

Hypereosinophilic Syndrome

Hypereosinophilic syndrome (HES) is a condition characterized by peripheral blood eosinophilia with manifestations of organ system involvement or dysfunction directly related to eosinophilia in the absence of parasitic, allergic, or other secondary causes of eosinophilia.

Secondary eosinophilia is a cytokine-derived (interleukin-5 [IL-5]) reactive phenomenon. Worldwide, parasitic diseases are the most common cause, whereas, in developed countries, allergic diseases are the most common cause. 

Other causes of eosinophilia include the following:

  • Malignancies – Metastatic cancer, T-cell lymphoma, colon cancer
  • Pulmonary eosinophilia – Loffler syndrome, Churg-Strauss syndrome, allergic bronchopulmonary aspergillosis
  • Connective tissue disorders – Scleroderma, polyarteritis nodosa
  • Skin diseases – Dermatitis herpetiformis
  • Inflammatory bowel disease
  • Sarcoidosis
  • Addison disease

Eosinophils in the peripheral blood of a patient with idiopathic eosinophilia.

Hypereosinophilic syndrome is a myeloproliferative disorder characterized by persistent eosinophilia that is associated with damage to multiple organs. 

Hypereosinophilic syndrome is traditionally defined as peripheral blood eosinophilia > 1500/mcL (> 1.5 × 109/L) persisting ≥ 6 months.

In 1975, Chusid et al defined the three features required for a diagnosis of hypereosinophilic syndrome:

  • A sustained absolute eosinophil count (AEC) greater than >1500/µl, which persists for longer than 6 months
  • No identifiable etiology for eosinophilia
  • Signs and symptoms of organ involvement

Hypereosinophilic syndrome was previously considered to be idiopathic but is now known to result from various disorders, some of which have known causes. One limitation of the traditional definition is that it does not include those patients with some of the same abnormalities (eg, chromosomal defects) that are known causes of hypereosinophilic syndrome but who do not fulfill the traditional hypereosinophilic syndrome definition for degree or duration of eosinophilia. Another limitation is that some patients with eosinophilia and organ damage that characterize hypereosinophilic syndrome require treatment earlier than the 6 months necessary to confirm the traditional diagnostic criteria. Eosinophilia of any etiology can cause the same types of tissue damage.

Hypereosinophilic syndrome is rare, has an unknown prevalence, and most often affects people age 20 through 50. Only some patients with prolonged eosinophilia develop organ dysfunction that characterizes hypereosinophilic syndrome. Although any organ may be involved, the heart, lungs, spleen, skin, and nervous system are typically affected. Cardiac involvement can cause significant morbidity and mortality.

Symptoms of hypereosinophilic syndrome:

The signs and symptoms of hypereosinophilic syndrome can vary significantly depending on which part(s) of the body are affected. Frequent symptoms listed by body system include:

  • Skin – rashes, itching, and edema.
  • Lung – asthma, cough, difficulty breathing, recurrent upper respiratory infections, and pleural effusion.
  • Gastrointestinal – abdominal pain, vomiting, and diarrhea.
  • Musculoskeletal – arthritis, muscle inflammation, muscle aches, and joint pain.
  • Nervous system – vertigo, paresthesia, speech impairment, and visual disturbances.
  • Heart – congestive heart failure, cardiomyopathy, pericardial effusion, and myocarditis.
  • Blood – deep venous thrombosis, and anemia.

Affected people can also experience a variety of non-specific symptoms such as fever, weight loss, night sweats, and fatigue.

hypereosinophilic syndrome

Hypereosinophilic Syndrome

Hypereosinophilic syndrome with cardiac involvement marked by a myocardial thickening (A, arrows), which resolved after corticosteroid treatment (B, arrows).


Jane Liesveld and James P. Wilmot. Hypereosinophilic Syndrome – Hematology and Oncology – MSD Manual Professional Edition https://www.msdmanuals.com/professional/hematology-and-oncology/eosinophilic-disorders/hypereosinophilic-syndrome?query=Hypereosinophilic%20Syndrome

What causes secondary eosinophilia? https://www.medscape.com/answers/202030-115250/what-causes-secondary-eosinophilia?

Eosinophilia. https://en.wikipedia.org/wiki/Eosinophilia

Hypereosinophilic syndrome. https://rarediseases.info.nih.gov/diseases/2804/hypereosinophilic-syndrome

Noh HR, Magpantay GG. Hypereosinophilic syndrome. Allergy Asthma Proc. January 2017; 38(1):78-81.

Curtis C, Ogbogu P. Hypereosinophilic Syndrome. Clin Rev Allergy Immunol. April 2016; 50(2):240-251.

Fiona Larsen. Hypereosinophilic Syndrome. https://dermnetnz.org/topics/hypereosinophilic-syndrome

Venkata Anuradha Samavedi, MBBS, MD. Hypereosinophilic Syndrome. Medscape Reference. March 2017; http://emedicine.medscape.com/article/202030-overview.

Idiopathic Hypereosinophilic Syndrome with Löeffler’s Endocarditis – Scientific Figure on ResearchGate. Available from: https://www.researchgate.net/figure/Hypereosinophilic-syndrome-with-cardiac-involvement-in-our-patient-was-marked-by-a_fig2_263282480 [accessed 12 Oct, 2021]

Looman KIMNuver MEKorevaar TIM, et al
Hypereosinophilic syndrome with multiorgan involvement: an interdisciplinary work-up

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