The idiopathic Hypereosinophilic Syndrome (HES)can be diagnosed if certain findings are identified and alternative diagnoses have been excluded.


Key features:

(1) chronic eosinophilia

(2) exclusion of alternative diagnoses

(3) absence of clonal proliferation of eosinophils


The primary distinction from the chronic eosinophilic leukemia (CEL, previous section) is the absence of clonality in the eosinophils (including no excess of bone marrow or circulating blasts).


Features of chronic eosinophilia:

(1) absolute eosinophil count >= 1,500 per µL

(2) involve mature eosinophils

(3) duration >= 6 months



(1) reactive eosinophilia (allergy, parasites, autoimmune, etc.)

(2) neoplastic hematologic disorder with a reactive eosinophilia (T cell lymphoma, Hodgkin's disease, non-Hodgkin's lymphoma, ALL, mastocytosis)

(3) acute myeloid leukemia (AML)

(4) myelodysplastic disorders

(5) other myeloproliferative disorders (polycythemia, primary thrombocytosis, CML, myelofibrosis)

(6) aberrant T cell proliferations with abnormal cytokine production

(7) presence of Philadelphia chromosome and/or bcr-abl on cytogenetics

(8) blasts > 5% of nucleated cells in the bone marrow (a higher percent favors CEL)


Exclude clonal proliferation: neither of the following should be present:

(1) clonal chromosomal abnormality

(2) other evidence of clonality


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