ABSTRACT
Chronic eosinophilic leukemia (CEL) is a very rare myeloproliferative neoplasm (MPN) characterized by clonal proliferation of eosinophil precursors leading to persistent eosinophilia in blood, bone marrow (BM), and peripheral tissues [1–6]. Diagnosis of CEL requires sustained eosinophil count ≥1.5 × 109/L in the blood, blasts are <20% (blood or BM), exclusion of specific neoplasms that may be associated with eosinophilia (e.g., acute myeloid leukemia with inv16, BCR-ABL+ chronic myeloid leukemia [CML], polycythemia vera [PV], essential thrombocythemia [ET], primary myelofibrosis [PMF], chronic neutrophilic leukemia [CNL], chronic myelomonocytic leukemia [CMML], BCR-ABL1− atypical CML [aCML], myelodysplastic syndrome, and MPNs with PDGFRA, PDGFRB, or FGFR1), evidence of clonality by chromosomal, or molecular studies or increased blasts (≥2% in blood and ≥5% in BM) [1–3,6]. Cases with sustained eosinophilia but without evidence of clonality or increased blasts (<2% in blood and <5% in BM) are classified as hypereosinophilic syndrome (HES). Cases fulfilling the criteria for HES but without tissue damage are classified as idiopathic hypereosinophilia. The clinical presentation of HES/CEL is variable with cardiovascular, cutaneous, and/or neurologic systems being most often involved. CEL is a multisystem disorder with eosinophilia and tissue infiltrate by eosinophils leading to organ damage. Some patients have constitutional symptoms such as fever, fatigue, muscle pain, pruritus, angioedema, and diarrhea. Serious complications include endomyocardial fibrosis (leading to restrictive cardiomyopathy), scaring of the heart valves, peripheral neuropathy, and pulmonary dysfunction.
