Key features:
(1) chronic eosinophilia
(2) exclusion of alternative diagnoses
(3) demonstration of a clonal proliferation of eosinophils
The primary distinction from the idiopathic hypereosinophilic syndrome is the presence of clonality in the eosinophils.
Features of chronic eosinophilia:
(1) absolute eosinophil count >= 1,500 per µL
(2) involve mature eosinophils
(3) duration >= 6 months
Exclusions:
(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 >= 20% of nucleated cells in the bone marrow
Demonstrate clonal proliferation - one or both of the following:
(1) clonal chromosomal abnormality
(2) other evidence of clonality
