Hypereosinophilic Syndrome (HES) / Chronic Eosinophilic Leukemia (CEL)

Eosinophilia is defined by > 0.5 x 109 cells/L, hypereosinophilia by >1.5 x 109 cells/L .
H(yper)E(osinophilic)S(yndrome) can be subclassified in 3 catagories:
– primary (or neoplastic; clonal expansion caused by myeloid, stem cell or eosinophilic neoplasm)
– secondary (reactive; typically found in parasitic infections, solid tumours, Hodgkin’s lymphoma, T-cell lymphomas – Lymphocytic variant HES (L-HES)- , drug induced)
– idiopathic (underlying cause remains unknown).
Primary HES (or CEL) often has rearrangement of FIP1L1-PDGFRA or PDGFRB, but FGFR1 and JAK2 rearrangement can also be found.

Morphological eosinophilic abnormalities lack sufficient specificity to differentiate a neoplastic process from a reactive eosinophilia; increased BM eosinophils were seen in the majority of all the cases, along with morphological abnormalities. These include in blood film degranulation, vacuolisation or hyperlobulation, and bone marrow shows increased eosinophils and precursors, often these eosinophils also contain basophilic granules.