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Hypereosinophilic syndrome

Eosinophils are blood cells in the leukocyte family (also referred to as white blood cells). They are found in all individuals in low numbers (< 500/mm3 of blood). Moderate eosinophilia refers to a figure of between 0.5 and 1.5 G/L. If the level increases to over 1,500/mm3, one refers to hypereosinophilia.
Blood HE and/or in the organs requires methodical investigations based on interviews, the clinical/biological context and the characteristics of the HE so that a diagnosis can be made. Apart from parasite, allergy or drug-related causes, which are the ones most frequently observed, there are forms of hypereosinophilia that occur during a range of affections (immune system diseases, hemopathy or cancer). If an exhaustive investigation proves to be fruitless, the hypothesis of a hypereosinophilic syndrome (HES) has to be raised (1).

What are the symptoms?

Eosinophils, once in the blood, may infiltrate all tissue and/or organs. It should be mentioned that all patients may suffer from asymptomatic chronic hypereosinophilia, which means that no organs have been affected.
The organs and tissue most frequently affected are the skin, lungs and digestive tract. It is more serious if the nervous system and heart are affected, but this is only observed in 20% of patients.
Skin manifestations vary greatly: pruritus, skin rashes, nodules, mucous ulcerations, and oedema. If the digestive system is affected, the patient may suffer abdominal pain, diarrhoea or ascites (liquid in the abdominal cavity, which increases the abdominal perimeter). A chronic cough, asthma, breathlessness, detectable anomalies on an x-ray or scan of the lungs show that the respiratory system has been affected.

What is the diagnosis?

The diagnosis relies on confirming an increase in eosinophils at least twice in the blood.
The investigation, therefore, meets the following objectives:

Test for damage to the organs, in particular the heart, sometimes requiring an organ biopsy (colon, stomach, skin) to confirm the presence of eosinophils in the tissue.
Test for the cause for hypereosinophilia. Once the usual causes have been ruled out (medication, parasites, cancer, and immune system diseases), more in-depth exploratory procedures in a specialist environment will be necessary to confirm HES: bone marrow biopsy, molecular anomaly of the eosinophils, t-cell anomalies. These tests will differentiate the different kinds of HES (2):
- Clonal eosinophils which are often a sign of chronic eosinophilic leukaemia (previously referred to as myeloproliferative HES)
- Lymphoid HES, or hypereosinophilia, is actually a sign of a T-cell malfunction (another type of white blood cell)
- Unexplained HES, which account for about half of all cases of HES

In a majority of cases, HES are chronic diseases requiring lengthy treatment.

What treatments are available?

If the hypereosinophilia cannot be explained, and the organs are not affected, once it has been ascertained that the heart has not been affected, simple blood (and eosinophil count) monitoring, without treatment, is usually offered.

In the case of clonal eosinophilia, drugs such as imatinib (Glivec) can be remarkably effective, especially if an anomaly affecting the PDFFRA gene is identified (FIP1L1-PDGFRA).

In the majority of other situations, corticosteroid treatment is usually effective, at least to start with.

If the hypereosinophilia persists despite the corticosteroid treatment, or it reappears if the steroid treatment is reduced, so-called second-line treatments will then be proposed: