PURPOSE OF REVIEW: Hypereosinophilic syndrome (HES) is characterized by 
persistent hypereosinophilia associated with end-organ damage. As our 
understanding of the pathogenesis of various forms of HES broadens, so does our 
ability to tailor steroid-sparing therapies for each subtype. The purpose of 
this review is to summarize recent literature related to the etiology, 
diagnosis, and management of HES.
RECENT FINDINGS: Mutations involved in subsets of HES can guide the choice of 
tyrosine kinase inhibitors beyond just imatinib. Several biologics that target 
interleukin-5 or its receptor have shown beneficial and selective 
eosinophil-reducing effects in clinical trials for asthma and other disorders 
including HES. Early clinical data with emerging therapies such as 
dexpramipexole and anti-Siglec-8 antibody show promise, but need to be confirmed 
in randomized trials. Several new biologics and tyrosine kinase inhibitors have 
been shown to lower eosinophil numbers, but more randomized trials are needed to 
confirm efficacy in HES.