Abstract
Hypereosinophilic syndromes (HES) are rare, heterogeneous syndromes characterized by markedly elevated eosinophil counts in the blood and/or tissue and evidence of eosinophil-associated pathology. Although parasitic infections, drug hypersensitivity, and other disorders of defined etiology can present as HES (associated HES), treatment is directed at the underlying cause rather than the eosinophilia itself. A number of additional subtypes of HES have been described, based on clinical and laboratory features. These include (1) myeloid HES—a primary disorder of the myeloid lineage, (2) lymphocytic variant HES—eosinophilia driven by aberrant or clonal lymphocytes secreting eosinophil-promoting cytokines, (3) overlap HES—eosinophilia restricted to a single organ or organ system, (4) familial eosinophilia—a rare inherited form of HES, and (5) idiopathic HES. Since clinical manifestations, response to therapy, and prognosis all differ between HES subtypes, this review will focus on clinical and biological markers that serve as markers of disease activity in HES (excluding associated HES), including those that are likely to be useful only in specific clinical subtypes.
Highlights
Hypereosinophilic syndromes (HES) are defined by the presence of hypereosinophilia [absolute eosinophil count (AEC) > 1,500/μL or marked tissue eosinophilia] and eosinophil-associated clinical manifestations
HES can occur in the context of defined disorders, such as drug hypersensitivity, helminth infection, and neoplasia, for which specific treatment of the underlying secondary cause leads to resolution of the eosinophilia, for the purposes of this review, HES refers to all clinical subtypes of HES with the exception of associated HES
The development of standardized clinical assessments of disease activity, such as patient-reported outcomes (PROs) and clinician-reported outcomes (ClinROs), that can be used to guide treatment and serve as clinical trial endpoints has been complicated in HES due to the heterogeneity of disease across HES subtypes and organ systems and the rarity of the disorder itself
Summary
Hypereosinophilic syndromes (HES) are defined by the presence of hypereosinophilia [absolute eosinophil count (AEC) > 1,500/μL or marked tissue eosinophilia] and eosinophil-associated clinical manifestations. The AEC normalizes with effective therapy in MHES and can be used to monitor disease activity, data from chronic myelogenous leukemia and drug interruption trials in PDGFRAassociated HES suggest that molecular monitoring is preferable when possible since molecular relapse may precede hematologic (and clinical) relapse by several months [71] This is important in view of recent data demonstrating sustained remission after imatinib discontinuation in some patients [72,73,74]. Eosinophilic Granulomatosis with Polyangiitis Several studies have examined the use of standard laboratory markers of inflammation, including erythrocyte sedimentation rate and C-reactive protein, in EGPA These markers have been shown to be elevated in active disease at the population level, a longitudinal study using a validated ClinRO as the gold standard found that they were affected by disease severity and treatment status, limiting their success in predicting disease activity and relapse at the individual patient level [77]
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