Hypereosinophilia (Including Chronic Eosinophilic Leukemia)

Chapter: Hypereosinophilia (Including Chronic Eosinophilic Leukemia)
McMaster Section Editor(s): Mark Crowther
Section Editor(s) in Interna Szczeklika: Andrzej Hellmann, Bogdan Ochrem
McMaster Author(s): Michael Trus, Mark Crowther
Author(s) in Interna Szczeklika: Andrzej Hellmann, Witold Prejzner
Additional Information

Definition, Etiology, PathogenesisTop

Hypereosinophilia (HE) is defined as particularly high peripheral eosinophil counts (≥1500/microL) and/or eosinophilic infiltration of one or more target tissues or organs. In the case of target organ damage, hypereosinophilic syndrome (HES) is diagnosed. HE/HES may be nonneoplastic (reactive, congenital, or idiopathic) or neoplastic (clonal; very rare).

Chronic eosinophilic leukemia (CEL) is a myeloproliferative neoplasm and subtype of HES in which uncontrolled clonal proliferation of eosinophil precursors causes hypereosinophilia of peripheral blood with eosinophilic infiltration of bone marrow and other tissues. In the 2008 World Health Organization classification of chronic myeloproliferative neoplasms, cases with PDGFRA, PDGFRB, and FGFR1 mutations were excluded from this clinical entity, which is now called chronic eosinophilic leukemia not otherwise specified (CEL-NOS).

Primary HE/HES: Conditions with eosinophils present as part of a malignant clone (myeloproliferative neoplasms, acute myeloid leukemia [AML]).

Secondary (reactive) HE/HES: Parasitic infections, allergic reactions, drug-induced (allergic or toxic) reactions. Less commonly, pulmonary eosinophilia, graft-versus-host disease, Hodgkin lymphoma, peripheral T-cell lymphomas, Langerhans cell histiocytosis, indolent systemic mastocytosis, solid tumors, allergic bronchopulmonary aspergillosis, chronic inflammatory diseases (eg, inflammatory bowel disease), systemic connective tissue diseases (allergic angiitis and granulomatosis [Churg-Strauss syndrome], other systemic vasculitis syndromes, deep eosinophilic fasciitis with eosinophilia), lymphocytic variant HES (caused by clonal T-cell cytokine production).

Clinical Features and Natural HistoryTop

1. Symptoms:

1) General symptoms are caused by a massive release of cytokines from eosinophils and include fatigue, fever, sweating, anorexia, and weight loss.

2) Cardiovascular symptoms (observed in ~20% of patients) are caused by myocardial and endocardial necrosis and fibrosis, as well as by subendocardial thrombosis. They include valvular regurgitation (most commonly mitral and tricuspid), features of restrictive cardiomyopathy, arrhythmias, conduction disturbances, thromboembolic events, and heart failure.

3) Respiratory symptoms (~50% of patients) are caused by eosinophilic infiltrates, pulmonary fibrosis, heart failure, or pulmonary embolism and include chronic nonproductive cough and dyspnea.

4) Cutaneous symptoms (~60% of patients) include angioedema, erythema, urticaria, subcutaneous papules and nodules, and pruritus.

5) Gastrointestinal symptoms (~30% of patients) are associated with mucosal ulcerations, bleeding, perforation, cholecystitis, and eosinophilic gastritis/gastroenteritis; they include diarrhea and abdominal pain.

6) Neurologic symptoms (~55% of patients) include behavioral abnormalities, memory impairment, ataxia, and features of peripheral polyneuropathy.

7) Other symptoms include hepatomegaly and/or splenomegaly, myalgia and arthralgia (caused by release of proinflammatory cytokines from eosinophils), and visual disturbances (caused by retinal thrombosis).

2. Natural history: The disease is chronic. In some cases, the course may be mild, but most frequently it is progressive and may rapidly lead to death due to organ involvement (usually heart failure) or transformation to acute leukemia.


Diagnostic Tests

1. Complete blood count: Eosinophilia (arbitrarily classified absolute eosinophil counts: mild, 500-1500/microL; moderate, 1500-5000/microL; severe, >5000/microL; the average peak eosinophil count in HES is ~6600/microL), anemia (~50% of patients), thrombocytopenia (~30%) or thrombocytosis (~15%), monocytosis, and moderate leukocytosis (in particular in patients with CEL).

2. Bone marrow examination: Aspiration reveals increased proportions of eosinophils, which in some patients are accompanied by dysplasia of megakaryocytes and granulocytes. Trephine biopsy reveals hypercellular marrow, expansion of megakaryopoietic and neutrophil granulocytic lineages, as well as increased amounts of reticulin fibers. Immunophenotyping and immunohistochemical (positive tryptase) studies are also performed.

3. Cytogenetic and molecular studies are performed to document clonal expansion (see Diagnostic Criteria, below). In some patients, the FIP1L1-PDGFRA fusion gene is found.

4. Other laboratory tests: IgE levels are elevated in patients with idiopathic hypereosinophilia (including the majority of patients with the lymphocytic variant) and usually normal in patients with CEL-NOS. The activity of granulocyte alkaline phosphatase is increased (>100 U) in patients with CEL-NOS.

5. Histology: Inflammatory eosinophilic infiltrates are found in biopsy samples of the affected organs.

Diagnostic Criteria


1) Eosinophilia ≥1500/microL.

2) Absence of the Ph chromosome, BCRABL1 fusion gene, and exclusion of other myeloproliferative (polycythemia vera, essential thrombocytosis, primary myelofibrosis) or myelodysplastic-myeloproliferative (chronic myelomonocytic leukemia, atypical chronic myelogenous leukemia) neoplasms.

3) Absence of t(5;12)(q31-35;p13) or other PDGFRB gene rearrangements.

4) Absence of the FIP1L1-PDGFRA fusion gene or other PDGFRA gene rearrangements.

5) Absence of FGFR1 gene rearrangements.

6) Less than 20% blasts in peripheral blood and bone marrow, absence of inv(16)(p13q22), t(16;16)(p13;q22), or other features that warrant the diagnosis of AML.

7) Presence of a clonal or cytogenetic abnormality, >2% blasts in peripheral blood, or >5% blasts in bone marrow.

2. Neoplasms with a PDGFRA gene rearrangement:

1) A myeloid (most frequently CEL, less often AML) or less commonly lymphoid (T-lymphoblastic lymphoma) neoplasm with significant eosinophilia.

2) Presence of the FIP1L1-PDGFRA fusion gene.

Differential Diagnosis

Disorders of the organs affected in HES (see Clinical Features, above).


1. In patients with eosinophil counts <5000/microL and no organ involvement, cytoreduction is not necessary.

2. HE with the FIP1L1-PDGFRA gene: Imatinib. Patients with cardiac involvement should receive concomitant glucocorticoids when therapy with imatinib is initiated to prevent acute cardiac injury.

3. HES without a PDGFRA rearrangement: Glucocorticoids, for instance, prednisone 1 mg/kg until eosinophil counts decrease <1500/microL and symptom control is achieved; then slowly taper the dose. Patients at risk for infection with Strongyloides as a cause of HES should receive ivermectin (200 microg/kg/d for 2 days) concomitantly with glucocorticoids to avoid dissemination of infection.

4. In patients not responding to treatment and patients with CEL-NOS: Cytotoxic agents (hydroxyurea [INN hydroxycarbamide]; if ineffective, interferon alpha, then vincristine or etoposide). In patients with no response to these agents, use experimental treatments (mepolizumab, alemtuzumab) or consider allogeneic hematopoietic stem cell transplantation. In patients with high eosinophil counts, use glucocorticoids, as above. Rarely leukapheresis may be considered.


Complete blood count (target eosinophil counts <1500/microL); other studies relevant to organ involvement (including echocardiography) every 6 to 12 months. In patients with the FIP1L1/PDGFRA gene, perform molecular studies every 3 months if indicated to monitor response to therapy or to determine if remission is durable in patients obtaining a complete molecular response.


The majority of patients with idiopathic HES have a good response to glucocorticoids in monotherapy and in combination with hydroxyurea, and patients who are refractory to these treatments respond to other modalities listed above (5-year survival rates are up to 90%). Patients with the FIP1L1/PDGFRA gene have a very good response to imatinib. In the case of CEL-NOS, the prognosis is poor; in half of these patients, transformation to AML occurs and the mean survival is 22 months.

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