Hypereosinophilic syndrome (HES) is defined by 1) blood hypereosinophilia (HE), 2) HE-attributable organ damage/dysfunction and 3) the absence of other conditions or disorders which may be responsible for organ impairment. The lymphocytic variant of HES (L-HES) exhibits several features of reactive HES and is defined by the presence of an aberrant T-cells overproducing interleukin-5 (IL-5) or rarely other cytokines. Of note is, that the clonal T-cell receptor (TCR) by polymerase chain reaction (PCR) are frequently observed in these abnormal T-cells, but it is not a rule [1].
