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The hypereosinophilic syndrome (HS) is a disease process characterized by a persistently elevated eosinophil count (= 1500 eosinophils/mm³) in the blood for at least six months without any recognizable cause after a careful workup, with evidence of involvement of either the heart, nervous system, or bone marrow.[1] Although HS has no certain aetiology, evidence suggests a link with chronic eosinophilic leukemia[2] as it shows similar characteristics and genetic defects.[3] Recent studies have shown that Mepolizumab may be effective in treating patients with hypereosinophilic syndrome.[4]
In the heart, there are two forms of the hypereosinophilic syndrome, endomyocardial fibrosis and Loeffler’s endocarditis.
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.[3] 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.[3] Roughly 50% of patients with HS also have anaemia.[3]
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.[3] Chest radiographs may indicate pleural effusions and/or fibrosis[3], and neurological tests such as CT scans can show strokes and increased cerebrospinal fluid pressure.[3]
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.[7]
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