Hypereosinophilic Syndrome Treatment & Management

Updated: Jul 13, 2022
  • Author: Venkata Anuradha Samavedi, MBBS, MD; Chief Editor: Emmanuel C Besa, MD  more...
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Approach Considerations

Whether and how to treat symptomatic hypereosinophilic syndrome depends on the clinical presentation, laboratory findings, and mutational analysis. [33] Currently, treating asymptomatic patients with hypereosinophilic syndrome is not recommended, as treatment itself is not without risks. Such patients are closely monitored with serum troponin measurements every 3-6 months, and echocardiography and pulmonary function tests every 6-12 months.

In contrast, cases of hypereosinophilic syndrome with myeloproliferative features, particularly those with FIP1L1/PDGFRA mutation, should be treated aggressively. These patients carry a worse prognosis without treatment.

In all patients without  FIP1L1/PDGFRA mutation, glucocorticoids are the first-line therapy. [3] About one third of these cases do not respond to steroids. In such patients, interferon alpha and hydroxyurea are the recommended second-line drugs. [34] For third-line therapy, high-dose (400 mg/d) imatinib is the treatment of choice.

For patients with  FIP1L1/PDGFRA mutation, imatinib is the drug of choice. The response rate in these cases approaches 100% in various studies.

Mepolizumab, a humanized monoclonal antibody specific for interleukin-5 (IL-5), is the first treatment shown to reduce disease flares in patients with FIP1L1/PDGFRA-negative hypereosinophilic syndrome. In a phase III study of mepolizumab, the proportion of patients experiencing one or more flares or withdrawing early from the study was 28% with mepolizumab versus 56% with placebo (P=0.002). [35] In 2020, the US Food and Drug Administration approved mepolizumab for adults and pediatric patients aged ≥12 years with hypereosinophilic syndrome for 6 months without an identifiable nonhematologic secondary cause. [36]  

For hypereosinophilic syndrome that is refractory to the usual treatments, chemotherapeutic agents that have been used with some success include chlorambucil, etoposide, vincristine, and cladribine and cytarabine. However, alkylating agents are usually avoided, because of their potential to induce leukemias.

Alternatively, in refractory cases, particularly those resistant to imatinib therapy, hematopoietic stem cell transplantation (HSCT) has been shown to reverse the organ dysfunction. However, because of the limited experience and complications associated with HSCT, its routine use is not justified at the present time.

Recurrent thromboembolic complications occur despite anticoagulant therapy in hypereosinophilic syndrome. Currently, there are no recommendations for prophylactic use of aspirin or warfarin in the absence of documented thrombi in hypereosinophilic syndrome.

Leukapheresis is indicated as an emergency therapy in hypereosinophilic syndrome to control symptoms due to hyperleukocytosis.

Consult a hematologist to assist with the diagnosis, management, and follow-up care of patients with unexplained eosinophilia.


Surgical Care

Management of cardiovascular disease

Valve replacement with bioprosthetic valves may be required in patients with hypereosinophilic syndrome and regurgitant lesions. Risk of thrombosis with mechanical valves is very high in patients with hypereosinophilic syndrome despite therapeutic anticoagulation.

Endocardiectomy may be required for patients with endomyocardial fibrosis, and thrombectomy may be required for individuals with thrombosis.


Evidence of hypersplenism and pain due to splenic infarction are indications for splenectomy.



Due to the rapidity and reliability of its effect, a 5-day course of prednisone (1 mg/kg/d or 60 mg/d) is the initial treatment of choice for all FIP1L1/PGDFRA– negative patients. Eosinopenia occurs within hours of steroid administration. Subsequently, prednisone is tapered from a daily dose to the lowest dose required on alternate days to maintain disease control.

Glucocorticoids decrease eosinophilopoiesis by suppressing the transcription of genes for interleukin-3 (IL-3), IL-5, and granulocyte macrophage colony-stimulating factor (GM-CSF). These agents also inhibit cytokine-dependent survival of eosinophils, resulting in their increased apoptosis. Steroids are also believed to increase rapid sequestration of eosinophils.

Almost 70% of patients with hypereosinophilic syndrome respond well to steroid therapy, especially those who present with urticaria and high IgE levels. Response to steroid therapy indicates a better prognosis.

A course of steroid therapy is also given to asymptomatic patients to establish hypereosinophilic syndrome responsiveness to steroids, in case rapidly progressive organ involvement develops in the future.

Steroids are also used in the management of imatinib-induced cardiogenic shock. In such circumstances, elevation of the serum troponin level or an abnormal echocardiographic study is an indication for starting steroids.



Imatinib mesylate (Gleevec) is the drug of choice for hypereosinophilic syndrome with FIP1L1/PDGFRA. A tyrosine kinase inhibitor, imatinib is also effective in patients with other mutations, such as BCR-ABLC-KIT, and PDGFRβ.

In patients with hypereosinophilic syndrome with FIP1L1/PDGFRA, imatinib induces clinical hematologic and molecular remission in the majority of cases. Resolution of symptoms and normalization of the eosinophil count occur within 1-2 weeks. Bone marrow abnormalities, including myelofibrosis, resolve within 1–2 months.

In contrast, structural abnormalities in the cardiovascular system and fixed neurologic deficits may not improve with imatinib therapy. However, imatinib is shown to arrest progression of endomyocardial fibrosis if therapy is initiated before the onset of structural abnormalities.

However, in true idiopathic hypereosinophilic syndrome (FIP1L1/PDGFRA negative), low-dose imatinib (100 mg/d) may not produce a durable remission. Response rates vary from 20% to 80%. This is thought to be due to alternate PDGFRA fusion partners. A higher dose (400 mg/d) is likely to produce partial to complete remission.

In addition, experience with imatinib in chronic myelogenous leukemia (CML) shows that it is not effective in eliminating the early progenitor cells in CML. Extrapolating these results to hypereosinophilic syndrome, lifelong therapy with imatinib would be required in the majority of patients. Because FIP1L1/PDGFRA–positive hypereosinophilic syndrome is predominantly a disease of young men and oligospermia is a complication of imatinib, sperm banking before initiation of therapy should be considered.

Other complications of imatinib include the following:

  • Neutropenia
  • Life-threatening eosinophilic myocarditis
  • Peripheral edema
  • Nausea
  • Muscle cramps
  • Bone pains
  • Rash

Molecular responsiveness to imatinib is assessed by screening for the PDGFRA mutation in the peripheral blood by fluorescent in situ hybridization (FISH) or reverse transcriptase–polymerase chain reaction (RT-PCR) at 3-6 month intervals in the first year and at 6-12 months intervals thereafter.

Khoury et al reported on features that predict responsiveness to treatment with imatinib, as indicated by eosinophil count < 1.5 x 109 L at 1 month and improvement in clinical symptoms. [37] Patient groups and response rates in their study were as follows:

  • FIP1L1-PDGFR myeloid neoplasm (FP) – 100%
  • PDGFRA-negative hypereosinophilic syndrome with four or more criteria suggestive of a myeloid neoplasm (MHES) – 54%
  • Steroid-refractory  PDGFRA-negative hypereosinophilic syndrome with fewer than four myeloid criteria – 0%

After patients who responded had remained in complete remission for at least 18 months, imatinib was tapered and discontinued in eight of the 16 FP patients and in one of the 13 with MHES. Six of the eight FP patients   and the patient with MHES remained in remission off therapy for a median of 29 months (range 14-36 months).

Resistance to imatinib has been reported in patients with a single-base (T6741) substitution in PDGFRA.  Bone marrow transplantation is an alternative in imatinib-resistant cases. [38] These patients have a dismal prognosis. [39]


Second-line Agents

Interferon alpha is a second-line drug of choice for patients whose condition does not respond to glucocorticoids. [40, 41, 42] Hydroxyurea has also demonstrated efficacy for steroid-refractory cases. [38]

Alemtuzumab, an anti-CD52 monoclonal antibody, has been shown to control symptoms as well as eosinophilia in patients with refractory hypereosinophilic syndrome. [43, 44]  Strati et al reported complete hematologic response (CHR) for a median duration of 66 weeks in 10 of 12 patients and for a median duration of 123 weeks in five of six patients retreated after relapse; time to progression was significantly longer in patients who received alemtuzumab maintenance therapy than in those who were only observed. [45]


Long-Term Monitoring

Periodically observe patients with hypereosinophilic syndrome to confirm that the eosinophilia is controlled and that no evidence of new or worsening organ involvement occurs. Patients should be advised to report any new or worsening symptoms.

Follow up patients with hypereosinophilic syndrome with serum troponin levels every 3 months, as well as with echocardiograms and pulmonary function tests every 6 months.