What is the clinical reasoning for eosinophilia?

From the Guidelines

Eosinophilia is most commonly caused by helminth infections in returning travelers and migrants from the tropics.

Clinical Reasoning

• The definition of eosinophilia is a peripheral blood eosinophil count of >0.45 10^9/L 1.
• Helminth infections are the most identifiable cause of eosinophilia, with rates varying from 14% to 64% 1.
• Common helminth infections causing eosinophilia include Strongyloides stercoralis and Schistosomiasis 1.
• Non-infectious causes of eosinophilia include drugs (non-steroidal anti-inflammatory drugs, beta-lactam antibiotics, nitrofurantoin), atopy (asthma, eczema, hay fever), and allergy 1.
• Long-standing moderate/high-grade eosinophilia (>1.5 10^9/L) can result in significant end organ damage 1.

Investigation and Management

• Concentrated stool microscopy and strongyloides serology should be performed on all patients with eosinophilia, regardless of geographic exposure 1.
• Empiric treatment with an antihelminthic agent such as albendazole may be considered in the absence of a specific diagnosis 1.
• Non-infective causes should be considered, particularly if the eosinophilia is persistent 1.

From the Research

Clinical Reasoning for Eosinophilia

The clinical reasoning for eosinophilia involves a comprehensive approach to diagnose and manage the condition. Eosinophilia is defined as a peripheral blood eosinophil count greater than 500 per microliter 2 or greater than 1.5 × 109 /L 3. The diagnostic procedure should include morphologic analysis of blood and bone marrow samples, cytogenetics, and fluorescence in situ-hybridization tests to detect evidence of an acute or chronic myeloid or lymphoid disorder 4, 5.

Causes of Eosinophilia

The causes of eosinophilia can be broadly divided into:

• Primary eosinophilia, caused by a cell-intrinsic mechanism originating from clonal expansion of eosinophils through acquisition of a somatic mutation, such as FIP1L1-PDGFRA 4, 5
• Secondary eosinophilia, which follows a cell-extrinsic mechanism as a response to exogenous cytokines, and is typically associated with non-hematological disorders such as infections, allergic conditions, connective tissue disorders, vasculitis, malignancy, or endocrinopathies 6, 4

Diagnostic Approach

The diagnostic approach to eosinophilia involves:

• Exclusion of secondary causes of eosinophilia 3
• Morphologic review of the blood and marrow 5, 3
• 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 5, 3
• Identification of the subtype of eosinophilia, which relies on a combination of various tests, including molecular analysis 3

Management of Eosinophilia

The management of eosinophilia depends on the underlying cause and severity of the condition. The goal of therapy is to mitigate eosinophil-mediated organ damage 3. Treatment options include:

• Watch and wait approach with close-follow-up for patients with milder forms of eosinophilia without symptoms or signs of organ involvement 3
• Imatinib for patients with rearranged PDGFRA or PDGFRB 3
• Corticosteroids as first-line therapy for patients with lymphocyte-variant hypereosinophilia and idiopathic hypereosinophilic syndrome (HES) 3
• Hydroxyurea and interferon-alfa as initial treatment and in steroid-refractory cases of HES 3
• Antibodies against interleukin-5 (IL-5) and the IL-5 receptor as a potential treatment option 3