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Hypereosinophilic syndrome
Classification and external resources

An eosinophil, the white blood cell involved in hypereosinophilic syndrome, seen amongst red blood cells.
ICD-10 D72.1 (ILDS D72.12)
ICD-9 288.3
ICD-O: 9964/3
OMIM 607685
eMedicine med/1076 derm/920
MeSH D017681

The hypereosinophilic syndrome (HS) is a disease characterized by a persistently elevated eosinophil count (≥ 1500 eosinophils/mm³) in the blood for at least six months without any recognizable cause, with involvement of either the heart, nervous system, or bone marrow.[1]

HS is a diagnosis of exclusion, after clonal eosinophilia (such as leukemia) and reactive eosionophilia (in response to infection, autoimmune disease, atopy, hypoadrenalism or cancer) have been ruled out. [2]

There are some associations with chronic eosinophilic leukemia[3] as it shows similar characteristics and genetic defects.[4]

If left untreated, HS is progressively fatal. It is treated with glucocorticoids such as prednisone.[2] The addition of the monoclonal antibody mepolizumab may reduce the dose of glucorticoids.[5]



In the heart, there are two forms of the hypereosinophilic syndrome, endomyocardial fibrosis and Loeffler's endocarditis.

  • Endomyocardial fibrosis (also known as Davies disease) is seen in tropical areas.[6][7]
  • Loeffler's endocarditis does not have any geographic predisposition.

Signs and symptoms

As HS affects many organs at the same time, symptoms may be numerous. Some possible symptoms a patient may present with include:


Numerous techniques are used to diagnose hypereosinophilic syndrome, of which the most important is blood testing. In HS, the eosinophil count is greater than 1.5 × 109/L.[4] On some smears the eosinophils may appear normal in appearance, but morphologic abnormalities, such as a lowering of granule numbers and size, can be observed.[4] Roughly 50% of patients with HS also have anaemia.[4]

Secondly, various imaging and diagnostic technological methods are utilised to detect defects to the heart and other organs, such as valvular dysfunction and arrhythmias by usage of echocardiography.[4] Chest radiographs may indicate pleural effusions and/or fibrosis[4], and neurological tests such as CT scans can show strokes and increased cerebrospinal fluid pressure.[4]

A proportion of patients have a mutation involving the PDGFRA and FIP1L1 genes on the fourth chromosome, leading to a tyrosine kinase fusion protein. Testing for this mutation is now routine practice, as its presence indicates response to imatinib, a tyrosine kinase inhibitor.[8]


Treatment primarily consists of reducing eosinophil levels and preventing further damage to organs.[4] Corticosteroids, such as Prednisone, are good for reducing eosinophil levels and antineoplastics are useful for slowing eosinophil production.[4] Surgical therapy is rarely utilised, however splenectomy can reduce the pain due to spleen enlargement.[4] If damage to the heart (in particular the valves, then prosthetic valves can replace the current organic ones.[4] Follow-up care is vital for the survival of the patient, as such the patient should be checked for any signs of deterioration regularly.[4] After promising results in drug trials (95% efficiency in reducing blood eosinophil count to acceptable levels) it is hoped that in the future hypereosinophilic syndrome, and diseases related to eosinophils such as asthma and Churg-Strauss syndrome, may be treated with the monoclonal antibody Mepolizumab currently being developed to treat the disease.[5] If this becomes successful, it may be possible for corticosteroids to be eradicated and thus reduce the amount of side effects encountered.[5]


HS is very rare, with only 50 cases being noted and followed up in the United States between 1971 and 1982.[4] The disease is even more uncommon within the paediatric population.[4]

Patients who lack chronic heart failure and those who respond well to Prednisone or a similar drug have a good prognosis.[4] However, the mortality rate rises in patients with anaemia, chromosomal abnormalities or a very high white blood cell count.[4]


  1. ^ Chusid MJ, Dale DC, West BC, Wolff SM (1975). "The hypereosinophilic syndrome: analysis of fourteen cases with review of the literature". Medicine (Baltimore) 54 (1): 1–27. doi:10.1097/00005792-197501000-00001. PMID 1090795. 
  2. ^ a b <New England Journal of Medicine 360:2005 (2009)
  3. ^ a b c d e f g h Longmore, Murray; Ian Wilkinson, Tom Turmezei, Chee Kay Cheung (2007). Oxford Handbook of Clinicial Medicine. Oxford. p. 316. ISBN 0-19-856837-1. 
  4. ^ a b c d e f g h i j k l m n o p Rothenberg, Mark E. "Treatment of Patients with the Hypereosinophilic Syndrome with Mepolizumab". Retrieved 2008-03-17. 
  5. ^ a b c Scheinfeld, Noah S. "Hypereosinophilic Syndrome". Retrieved 2008-02-15. 
  6. ^ Cotran, Ramzi S.; Kumar, Vinay; Fausto, Nelson; Nelso Fausto; Robbins, Stanley L.; Abbas, Abul K. (2005). Robbins and Cotran pathologic basis of disease. St. Louis, Mo: Elsevier Saunders. pp. 606. ISBN 0-7216-0187-1. 
  7. ^ Smedema JP, Winckels SK, Snoep G, Vainer J, Bekkers SC, Crijns HJ (December 2004). "Tropical endomyocardial fibrosis (Davies' disease): case report demonstrating the role of magnetic resonance imaging". Int J Cardiovasc Imaging 20 (6): 517–22. doi:10.1007/s10554-004-1095-9. PMID 15856635. 
  8. ^ Cools J, DeAngelo DJ, Gotlib J, et al. (2003). "A tyrosine kinase created by fusion of the PDGFRA and FIP1L1 genes as a therapeutic target of imatinib in idiopathic hypereosinophilic syndrome". N. Engl. J. Med. 348 (13): 1201–14. doi:10.1056/NEJMoa025217. PMID 12660384. 

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