EOSINOPHILIA See also Eosinophilia
GENERAL CLASSIFICATION OF EOSINOPHILIC DISORDERS
Blood eosinophilia can be classified as either
Infectious causes and noninfectious causes of secondary eosinophilia are prevalent in underdeveloped and developed countries, respectively.
Primary eosinophilia occurs primarily in males and is considered clonal in the presence of either cytogenetic evidence or bone marrow histological evidence of an otherwise defined neoplastic hematologic disorder.
Otherwise, a working diagnosis of idiopathic eosinophilia is made, and in the presence of both sustained eosinophilia (AEC =1500 cells/µL for at least 6 months) and target organ damage (eg, skin, heart, lung, nerve tissue), the process is subclassified as hypereosinophilic syndrome (HES).
Causes of Hpereosinophilia:
Classification and Causes of Blood Eosinophilia*
*CTD = connective tissue disease; HES = hypereosinophilic syndrome; PDGFR = platelet-derived growth factor receptor.
When both clinical and laboratory evaluations do not clearly identify either a secondary or a clonal cause, a working diagnosis of idiopathic eosinophilia is reasonable.
Familial eosinophilia is rare, and its genetic basis, at least in some cases, may be similar to that of clonal eosinophilia.
A diagnosis of clonal eosinophilia requires the presence of either cytogenetic evidence or bone marrow morphologic evidence for either acute leukemia or a chronic myeloid disorder (Table 1). Hematologic disorders that can be accompanied by clonal eosinophilia include acute myeloid leukemia,62 acute lymphocytic leukemia,63 chronic myeloid leukemia (CML),64 myelodysplastic syndrome,65 and both classic and atypical cases of myeloproliferative disorders (MPDs).66,67 The atypical MPD category includes chronic eosinophilic leukemia (CEL),68 systemic mastocytosis (SM),69 and chronic myelomonocytic leukemia (CMML).70 Recent developments in the molecular characterization of pathogenesis, in a subset of patients with clonal eosinophilia, have identified activating mutations of 3 receptor tyrosine kinase genes: PDGFRA, PDGFRB, and fibroblast growth factor receptor 1 (FGFR1).71
All patients with suspected primary eosinophilia should undergo bone marrow examination with cytogenetics.