What is the cause of eosinophilia (elevated eosinophil count)?

From the Guidelines

Eosinophilia should be managed by identifying and treating the underlying cause, with empirical treatment using albendazole 400 mg plus ivermectin 200 μg/kg considered for asymptomatic cases in returning travelers and migrants, as recommended by the UK guidelines 1, 2. When eosinophilia is detected, the primary approach is to identify and treat the underlying cause, which can include parasitic infections, allergic reactions, certain medications, autoimmune disorders, and hematologic malignancies.

• For parasitic infections, antiparasitic medications like albendazole or ivermectin are often prescribed, with the specific treatment depending on the type of infection and the patient's symptoms.
• In cases of allergic reactions, removing the allergen and using antihistamines or corticosteroids may help.
• For severe or hypereosinophilic syndrome, systemic corticosteroids like prednisone are typically used, with potential addition of hydroxyurea or interferon-alpha in resistant cases. The UK guidelines for the investigation and management of eosinophilia in returning travelers and migrants provide updated recommendations for the treatment of relevant pathogens and clinical conditions, including the use of empirical treatment with albendazole and ivermectin for asymptomatic eosinophilia 2.
• The guidelines also emphasize the importance of excluding Loa loa in people who have traveled to endemic regions before treating with ivermectin.
• Repeat treatment at 8 weeks may be necessary to treat any residual worms once they have developed into adults, as eggs and immature schistosomulae are relatively resistant to treatment 2. Overall, the management of eosinophilia requires a comprehensive approach that takes into account the underlying cause and the patient's symptoms, with the goal of preventing serious complications and improving quality of life.

From the Research

Definition and Classification of Eosinophilia

• Eosinophilia is a broad range of non-hematologic (secondary or reactive) and hematologic (primary, clonal) disorders with potential for end-organ damage 3, 4, 5.
• Hypereosinophilia has generally been defined as a peripheral blood eosinophil count greater than 1500/mm3 or 1.5 × 109 /L 3, 4, 5.
• The World Health Organization endorses a semi-molecular classification scheme of disease subtypes, including "myeloid/lymphoid neoplasms with eosinophilia and rearrangement of PDGFRA, PDGFRB, or FGFR1 or with PCM1-JAK2" and "chronic eosinophilic leukemia, not otherwise specified" (CEL, NOS) 3, 4, 5.

Diagnosis and Evaluation of Eosinophilia

• Diagnostic evaluation of primary eosinophilias relies on a combination of morphologic review of the blood and marrow, standard cytogenetics, fluorescence in situ-hybridization, flow immunophenotyping, and T-cell clonality assessment to detect histopathologic or clonal evidence for an acute or chronic hematolymphoid neoplasm 3, 4, 5.
• Disease prognosis relies on identifying the subtype of eosinophilia 3, 4, 5.
• A watch and wait approach with close-follow-up may be undertaken for patients with milder forms of eosinophilia without symptoms or signs of organ involvement 3, 4, 5.

Treatment and Management of Eosinophilia

• The goal of therapy is to mitigate eosinophil-mediated organ damage 3, 4, 5.
• Corticosteroids are first-line therapy for patients with lymphocyte-variant hypereosinophilia and idiopathic hypereosinophilic syndrome (HES) 3, 4, 5.
• Hydroxyurea and interferon-alpha have demonstrated efficacy as initial treatment and in steroid-refractory cases of HES 6, 3, 4, 5.
• Mepolizumab, an interleukin-5 (IL-5) antagonist monoclonal antibody, was recently approved by the US Food and Drug Administration for patients with idiopathic HES 5.
• The use of antibodies against interleukin-5 (IL-5) and the IL-5 receptor, as well as other targets on eosinophils, remains an active area of investigation 3, 4, 5.